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Building Tips and technical articles. => 1/2 A building. => Topic started by: Juan Valentin on May 01, 2019, 11:41:26 AM

Title: Cox.049 Piston lapping
Post by: Juan Valentin on May 01, 2019, 11:41:26 AM
Hello
               I`m posting here because I went to the engine set up and most of the threads are for bigger engines. I decided to do some lapping on my cox.049 engine because it is tight and I wanted to have a better fit. Is the first time I do this work,I read about it but no pictures were included so I decided to post a few of what I did. I took a piece of clear vinyl tubing and placed the conrod inside. I noticed where the hole on the conrod was inside the tubing and using an awl I punched a hole about 1/16 inch lower so when I pushed the pin thru it would hold the piston firmly. I used CRC 6-56 light oil and 3M white rubbing compound to lap the piston to the cylinder. I slowly worked the piston back and forth until I felt it was looser than previously. cleaned and lubed the piston and tried it. I felt it needed some more so I did more lapping until I was happy with the fit. The thing is to go slow checking fit often to avoid ruining your P/L. Here are pics.
                                                                                                                               Juan
Update:  Fred Von4  told me,Not seeing your technique...a HINT Lap in the piston cylinder with the piston skirt UP.... checking often that the Piston Top stops at TDC and takes a slight tap to fall free into the bore

IOW never reduce the top of the cylinder or top of the piston

Title: Re: Cox.049 Piston lapping
Post by: kenneth cook on May 02, 2019, 06:42:45 PM
          Juan, I have to ask, why is the anodizing removed where the cylinder meets the case? Did you lap the case to increase SPI? Or, was this done to orientate the exhaust cutouts? I have always gone the other direction by slightly raising the cylinder with cylinder shims. I found this worked better as it decreases SPI and reduces the piston crown height at top dead. I have had the piston crowns slightly strike glow heads on some engines, not by much. Just enough to continuously loosen the glow head after a flight or two.
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 03, 2019, 07:27:53 AM
Hello Ken & Motorman
                                               I removed material from the case to have the Exhaust outlets fore and aft and inlet ports to the sides. I used that .051 piston and cylinder to show how I used the Vinyl plastic tubing the engine I`m working on is a Cox.049 built out of parts I had. The crankcase is from a Black widow ,the cylinder is a number 1 I found,Diesel cranshaft,Killer Bee horseshoe mount  and a Galbreath head with nelson plug. I have been able to get 20,500 out of it running 25% nitro on an APC  4.75 x 4 prop but that is as far as I got. I have tried raising the Cylinder to change timing using shims and removing headgaskets to recoup compression. I have added more SPI by cutting the the piston and I have increased venturi area. I need to continue working on it, I read that the piston and cylinder to use is the Tee Dee number 4. I need to look thru my parts box to see If I have one. Are they available new from Cox vendors? Here are two pics of engine.
                                                                                                                                                                          Juan
Title: Re: Cox.049 Piston lapping
Post by: kenneth cook on May 03, 2019, 02:17:43 PM
           Juan, a #4 cylinder is a Tee Dee cylinder. That being said, there's so many variants of them, they can all perform differently. The benefit is the fluted porting alongside of the cutouts which can lend a bit more power. My preference though is the early thin walled Tee Dee. This cylinder always seemed to perform for me better than others. The rod also has a oil hole on the bottom. The rod itself has a color similar to aluminum. Regardless, a good fitting Black Widow or #1 cylinder will perform very very well. I have also had some good running Sure Starts, but they're very hit and miss. Some work good, others obviously better than others. It just takes exactly what your doing, a lot of playing around.
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 03, 2019, 03:16:25 PM
The piston is chromed. The cylinder is mild steel. Any material removed should be coming off the cylinder, not the piston. So technically, you are lapping the cylinder to the piston--or should be.

Some of the currently available "modified" product cylinders that have had TD exhaust ports cut into them will have a burr left from that secondary operation. It will chew up your engine. You can use a sacrificial piston to lap those cylinders around the port area. There's no reason to any higher if that is what you are repairing. The pistons are generally close enough size that the technique seems to work.

Looks like you are building a performance engine? Did you get the crank with the relieved journal? Without it, there will be extra drag from the bearing.

Divot
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 03, 2019, 06:00:52 PM
Hello Dave
                       I`m trying to get the best performance that I can.  There is a lot that I don`t know about how to get the most performance from the cox engine. I have had some knowledge from working on engines for quite a while as a hobby.  I have done some R/C Pylon racing and some On road R/C Car racing with my son which was a lot of fun and we won some trophies. I have over the years read with interest everything I could on engine work and it helped us to get some real good performance,efficiency and durability.
                          I would appreciate if you could post a picture of a crankshaft with a relived journal to have an idea of what was done.Thanks.
                                                                                                                                                                                     Juan
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 03, 2019, 10:12:46 PM
Juan,

I just assumed you were building a performance engine because you are using specific parts that can really help. The Galbreath head and Nelson plug in particular are a bolt-on improvement.

The only reason I mentioned the relieved crank is that some of the earlier "diesel cranks" had a constant diameter from the prop washer spline shoulder all the way to the crank disk. If you look at a stock Cox crankshaft, the shaft is undercut or relieved between the two ends. The full diameter is present at each end to provide a bearing surface, but cut away in the middle to reduce the running friction.

Also, some of the earlier "diesel cranks" had a full disk, and therefore poor balance. If you have one like that, just grind it to look like the Killer Bee crank. If you grind on it, do not overheat the metal and lose the temper.

I attached a picture I got somewhere of a regular Cox crank (left) and a Killer Bee crank (right). Both of these have the bearing relief. For a performance engine, the KB crank is highly preferred.  I don't have a picture of the earlier "diesel cranks" to show the differences.

Senor Cook is right on the money with his description of the "true Tee Dee" cylinder as having a separate flute that is a bit higher cut into the main bypass on each side. These are the best performing, in my experience. They are also harder to come by. If you can find new old stock, you are doing well. What has been offered are some product cylinders with the center exhaust web cut out. That is a waste of time, and damages the bore. Which was why I was thinking it might be the reason you were having to lap your cylinder.

Divot McSlow

Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 04, 2019, 12:12:57 PM
I stand corrected.

Divot
Title: Re: Cox.049 Piston lapping
Post by: bob whitney on May 04, 2019, 04:21:31 PM
also ,when lapping ,the lapping compound will in-bed itself in the soft material ( cylinder ) and take material off the harder part(piston)

if u want to take material off of the sleeve make a brass mandrill and lap the sleeve
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 04, 2019, 06:08:20 PM
Juan,

I just assumed you were building a performance engine because you are using specific parts that can really help. The Galbreath head and Nelson plug in particular are a bolt-on improvement.

The only reason I mentioned the relieved crank is that some of the earlier "diesel cranks" had a constant diameter from the prop washer spline shoulder all the way to the crank disk. If you look at a stock Cox crankshaft, the shaft is undercut or relieved between the two ends. The full diameter is present at each end to provide a bearing surface, but cut away in the middle to reduce the running friction.

Also, some of the earlier "diesel cranks" had a full disk, and therefore poor balance. If you have one like that, just grind it to look like the Killer Bee crank. If you grind on it, do not overheat the metal and lose the temper.

I attached a picture I got somewhere of a regular Cox crank (left) and a Killer Bee crank (right). Both of these have the bearing relief. For a performance engine, the KB crank is highly preferred.  I don't have a picture of the earlier "diesel cranks" to show the differences.

Senor Cook is right on the money with his description of the "true Tee Dee" cylinder as having a separate flute that is a bit higher cut into the main bypass on each side. These are the best performing, in my experience. They are also harder to come by. If you can find new old stock, you are doing well. What has been offered are some product cylinders with the center exhaust web cut out. That is a waste of time, and damages the bore. Which was why I was thinking it might be the reason you were having to lap your cylinder.

Divot McSlow

      Hello Dave
                       I have the later type of crank with the releif and cut outs. I will be searching thru the parts bin to see if I have one Tee Dee cylinder.  I was lapping the cylinder because it was tight about 1/8 to 3/16 from the top. I read what Paul Gibeault wrote and after washing the parts and devarnishing I did a little bit of lapping but still was tight 1/16 from the top so I did some more but have not run the engine anymore. I have seen the cylinder with the milled exhaust ports but have not acquired any. I might be wrong but after checking some new parts I bought I think are out of tolerance and might be parts cox didn`t use in their engines because of that. I had better luck with my junk pile or buying old low time engines.  There is something I would like to try and that is installing a bronze bushing on the case.
                       I have a Model Aviation issue with the Slyfox article you wrote,I liked very much and wish we had some control line racing locally but the guy`s at the club are precision aerobatics fans.Thanks for the reply.
                                                                                                                                                                     Juan
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 04, 2019, 06:14:57 PM
also ,when lapping ,the lapping compound will in-bed itself in the soft material ( cylinder ) and take material off the harder part(piston)

if u want to take material off of the sleeve make a brass mandrill and lap the sleeve
             Hello Bob
                               Thanks for the advice. I don`t know if I could make a brass mandrel precise enough to do the job but  I could try after all I have the time. Thanks again for the information I`m going to save it in my doc`s.
                                                                                                                                Juan
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 04, 2019, 06:21:01 PM
Cox pistons are not chrome plated.
                  Hello Motorman
                                            For a minute I thought they were hard chromed because when I was cutting the piston skirt for more SPI they were hard,maybe my cutting HSS bit is dull. Thanks for the info.
                                                                                                                                                                  Juan
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 04, 2019, 06:46:06 PM
Guys,

When the M&M man said they weren't chromed I had to go back to figure out why I said they were. It was probably an assumption I made based on what looked like a copper underplate that you can see on both the crown and the inside of the piston. So I took a file to the side of a piston to see. It is quite hard, but the one I scratched was not chromed. Not sure I see a lot of point in a thin copper plating on a piston....

I found Mr. Cook's comment about a drilled oil hole in early Cox .049 rods interesting. I can't recall ever seeing one like that. It must be a really small hole....  The oddest one I have run across so far are pistons with the rod clipped into the socket. Not peened in place, fastened with a clip. I bet those were not real long-lived.

Not sure if everyone has seen the aftermarket modification to the extruded Cox case wherein a bronze bushing was installed. I have a couple of cases like that, and wish I had more. For a while, I was spalling the cases on my Mouse Motors. So I have been patiently collecting used cases with damaged bores getting ready to do a batch of them--as soon as I figure out how. One of the key dimensions to hit is the location of the thrust face that the crank shoulders up to. All this would be pretty straightforward if you have the proper machinery, but in my case, I'd have to do it with just a drill press, reamer, and hand tools. No mill; no lathe.

Divot McSlow
Title: Re: Cox.049 Piston lapping
Post by: bob whitney on May 04, 2019, 07:24:26 PM
I am not sure of the exact natcher but the pistons are hardened . I believe Case hardend  I believe the copper coating is so only the sides of the piston are hardend,would need to go back and check but I believe the copper acts as a shield to keep the top of the piston from being hardening
coming back to me .that leaves the inside of the piston soft so it can be swedged around the rod ball y1
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 04, 2019, 08:08:56 PM
           Juan, a #4 cylinder is a Tee Dee cylinder. That being said, there's so many variants of them, they can all perform differently. The benefit is the fluted porting alongside of the cutouts which can lend a bit more power. My preference though is the early thin walled Tee Dee. This cylinder always seemed to perform for me better than others. The rod also has a oil hole on the bottom. The rod itself has a color similar to aluminum. Regardless, a good fitting Black Widow or #1 cylinder will perform very very well. I have also had some good running Sure Starts, but they're very hit and miss. Some work good, others obviously better than others. It just takes exactly what your doing, a lot of playing around.
                      Hello Ken
                                         I missed your post, I have seen the Tee Dee Cylinder with flutes on both sides somewhere in my stuff but have not found it. I did find a few cylinders with a single flute a little taller than the intake port and what looks like lightened pistons. I have never seen a conrod with an oil hole at the bottom. here is a pic of what I found.
                                                                                                                                                           Juan
                                       
Title: Re: Cox.049 Piston lapping
Post by: Larry Renger on May 04, 2019, 08:27:09 PM
The pistons were copper plated then ground on the outside so that the hardening process only effected the outside. That left the inside soft enough to swage the ball socket.

For good life and performance, it is ideal to reset the socket after break in. The ball and socket never had that great finish tolerances. Once done, probably good for the life of the engine.
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 04, 2019, 08:27:21 PM
Hello Bob and Dave
                                   I learn something new everyday thanks to you guys. Leroy Cox and Bill Atwood created an engine that is going to live forever I don`t think I will ever get rid of my cox .049 stuff. My first control line flight was on a Cox Tan P-40 Warhawk over 50 years back thru ebay I bought one in good shape just for the memories. Now if I could find an Avion Red P-51 Reno racer at an affordable price it would be the icing on the cake.
                                                                                                                                                               Juan
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 04, 2019, 09:05:53 PM
Thanks for the info Larry. That sounds vaguely familiar, so I think my memory buffer must be overflowing and dumping data....

For that process to make sense to me, it has to be a nitriding or oil quench hardening process. Do you recall what alloy the pistons were made out of? How about the cylinders?  I suspect the cylinders were from some type of free-machining alloy like SAE1118?

Dave
Title: Re: Cox.049 Piston lapping
Post by: Larry Renger on May 05, 2019, 07:41:04 AM
Niitriding
Title: Re: Cox.049 Piston lapping
Post by: kenneth cook on May 05, 2019, 07:53:56 AM
             I have several TD's with the oil hole in the rod. I believe these were the 60's TD's. They've also been the most successful engines for me. The thicker walled cylinders of the late 80's always proved problematic in terms of quality of run. I either had some that worked well or they didn't. What I noticed was that the piston seemed to swell and gall when I leaned them out. I would love to take a picture of the rod but this site is difficult for me to send pictures.
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 06, 2019, 09:05:43 PM
Hello Ken
                 I have the same problem posting photos on the CEF but here I find it easier. I wonder why they stopped drilling the rod maybe they found out it didn`t make much of a difference and decided to eliminate that step in making the rod.   Today I did a couple of runs on my Reedy.049 I have enlarged the venturi area but it did nothing for me the needle valve adjusting got kind of vague and I gained nothing. I replaced with a stock one I had and things Improved. I had done a little more lapping on the number 1 cylinder and that  helped me gain a couple of hundred revs now engine went to 20740 Rpm. I had cut the piston skirt when I raised the cylinder with shims to have some SPI now it has .025 inch measured with a feeler gauge with no shims under the cylinder. In the first run I noticed that the tach was reading about 14k, I had inadvertently switch my Fromeco tach to the 3 blades setting. The engine is wearing the crankcase as I can see metal residue in the oil coming out of the nose of the case. I previously had been taking the engine apart after making the runs and using Rislone engine oil supplement to lube the crank in hopes of reducing wear but I realized that as soon as the engine started the fuel and castor oil would be pushing  the Rislone out. I will continue trying still have cylinders to try.
                                                                                                                                                                                    Juan
Title: Re: Cox.049 Piston lapping
Post by: kenneth cook on May 07, 2019, 03:31:00 AM
            Juan, your experiments have me a wondering. I never did much playing around with reedies in terms of SPI. However, I've played with it a lot with TD's. This first became very noticeable when I bought a modified Sure Start with the lightened and cut piston skirt. These had so much SPI that the engine would run very erratic. I raised the cylinder with a stock aluminum shim that came with the QZ mufflers to eliminate SPI on Babe Bees. The engine took on a whole new attitude.I combined this setup with a lightened and balanced crankshaft and this engine is pretty amazing. What I did notice though was that reducing the SPI to about .012" and under made my TD run much better. I was able to obtain cylinder shims in increments of .001", .002", .004" from Darell Albert. These were originals from Kustom Kraftmanship.

            I have to ask is your metal particles coming from the drive plate appearing as though it's coming out of the nose? I have had this happen and to remedy this, I dusted down the nose a bit and obtained a stainless washer which is available through Cox International.
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 07, 2019, 02:13:48 PM
Be sure you understand what you are using a steel washer for on the front end. If you are trying to take up tolerances and end play in the crank, the washer ID has to fit over the crank. Too much end play may allow the crank pin to wipe out the rim on the metal tanks.

If your end play is already good, with no danger of contact with the tank (or you are using a plastic reed cap) then the C.I. washer would work to reduce the galling between the case and drive hub. If you insist on using an electric starter, this washer is needed to prevent short life of the parts. Another alternative would be to switch to the brass drive hub, which I heard was designed for a pusher application?

The washers I bought a few years back from Cox International had a smaller hole? That caused it to shoulder on the crank, not float on the journal. I talked to Bernie about it at the time to be sure he understood the issue. But I have not ordered any since then. The parts I purchased were P/N 49TWASH.

The cranks I have measured ran in the range of .2170 to .21760.  That is a pretty large variation for such a small diameter and trying to run a controlled clearance for the oil film.

Dave
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 07, 2019, 07:39:09 PM
            Juan, your experiments have me a wondering. I never did much playing around with reedies in terms of SPI. However, I've played with it a lot with TD's. This first became very noticeable when I bought a modified Sure Start with the lightened and cut piston skirt. These had so much SPI that the engine would run very erratic. I raised the cylinder with a stock aluminum shim that came with the QZ mufflers to eliminate SPI on Babe Bees. The engine took on a whole new attitude.I combined this setup with a lightened and balanced crankshaft and this engine is pretty amazing. What I did notice though was that reducing the SPI to about .012" and under made my TD run much better. I was able to obtain cylinder shims in increments of .001", .002", .004" from Darell Albert. These were originals from Kustom Kraftmanship.

            I have to ask is your metal particles coming from the drive plate appearing as though it's coming out of the nose? I have had this happen and to remedy this, I dusted down the nose a bit and obtained a stainless washer which is available through Cox International.




 Hello Ken
                  I already have the steel washer on the drive plate to avoid galling but I`m not using an electric starter to get the engine running. I`m a patient guy and use a cox spring starter to get it running. On the SPI I had cut the piston skirt to get SPI when I raised the cylinder. the shims I have .010 inch and after using two I had no SPI so I cut the piston. After I did that I didn`t gain anything so I took them out and then I realized I had a lot of SPI .025  I had lapped the piston some more and that in combination with the SPI got me 20,7k.  When the engine is at full song is when I see a little bit of residue.
                                                                                                                                                                        Juan
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 07, 2019, 08:00:52 PM
Be sure you understand what you are using a steel washer for on the front end. If you are trying to take up tolerances and end play in the crank, the washer ID has to fit over the crank. Too much end play may allow the crank pin to wipe out the rim on the metal tanks.

If your end play is already good, with no danger of contact with the tank (or you are using a plastic reed cap) then the C.I. washer would work to reduce the galling between the case and drive hub. If you insist on using an electric starter, this washer is needed to prevent short life of the parts. Another alternative would be to switch to the brass drive hub, which I heard was designed for a pusher application?

The washers I bought a few years back from Cox International had a smaller hole? That caused it to shoulder on the crank, not float on the journal. I talked to Bernie about it at the time to be sure he understood the issue. But I have not ordered any since then. The parts I purchased were P/N 49TWASH.

The cranks I have measured ran in the range of .2170 to .21760.  That is a pretty large variation for such a small diameter and trying to run a controlled clearance for the oil film.

Dave


Hello Dave
                    I have the steel ones with the small hole which I bought from Bernie and later from EX. I took a piece of S/S welding rod which is .125 and made a mandrel to attach 400 grit sandpaper to enlarge the hole on the washer to get it over the crank and I sanded the nose of the case to gain clearance. The cranks that I have are .2165 for the diesel type and .217 for the stock factory crank. The newer crankcases that I have seem to have a bigger hole for the crank by .001 inch That is why I have a lot of play when engine is hot. I didn`t want to hurt the engine using an electric starter,I`m using The factory spring starter and it has worked for me. I`m going to try doing a bronze bushed crankcase. I bought a reamer to get the bush to the right size from Mcmaster carr and other parts from other vendors and had them sent to my son in Miami to save on shipping. One of the items was delayed so I had to wait for a while but yesterday my son placed the things on the mail. I hope to have the parts soon.
                                                                                                                                                                                                 Juan
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 07, 2019, 08:48:27 PM

                Today I decided to convert a burned out Cox Hi compression glow plug to accept a Turbo glow plug. I got it done and decided to test the head on the engine I have been running with the Galbreath Nelson head. With the Cox head and a Novarossi 8 turbo plug all I could get was 18,500 Rpm. I tried a different brand number 7 turbo plug and I was able to get 19,700 Rpm. I did not have any other turbo plug available so I went back to the Galbreath Head with the nelson plug. The engine went back to running  20,600 Rpm. I will try to get other Turbo plugs to test but the nelson plug is the best and very durable. To do the turbo mod I used a small Sherline Lathe I have. I drilled the head with a bit with a collar and then used a M8 x 0.75 tap mounted on an aluminum holder I made to align the tap while cutting the threads. I cut the threads with the lathe off holding the chuck and turning the tap mounted on the lathe tailpost to get the best aligment. Without doing it like that I would have had trouble getting it right.Here are some pics.
                                                                                                                                                                                             Juan
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 07, 2019, 11:14:15 PM
Sweet!

You are doing a lot of cool stuff, Juan!

I don't recall hearing of anyone experimenting with Turbo plugs in a Cox. (Possibly Les Akre, of the Canadian Racing Contingent?)  I would think you would want the hottest plug you could get. (That is just a guess.)  So something like an OS P3 or P4, maybe. How did you machine the seat for the plug? With the centerdrill? The critical thing with the Nelson or the turbo plugs is to eliminate any airgaps from the fit/threads. Else, you lose performance. Which is one reason why every head that fits a standard glow plug performs worse than a Cox glow head. If the cavity in the turbo plug is too big, it will also change the performance. I have never looked at these side-by-side, so I don't know how they compare.

With your lathe, you can also buy/make a spring-loaded guide that you can chuck in the tailstock. It has a point on it that will engage in the back of a standard tap handle. That guarantees that the thread centerline is perpendicular to your workpiece. What you show looks like a rigid setup, which may cause some issues if the runout is very large. Starting a thread with a bottom tap looks like an interesting experience....

I look forward to reports on your work on the bushed cases. When I get a chance, I need to figure out how to do a bunch of those myself. There has been a bit of discussion about the best material type(s) for the bush. Bob Zambelli provided a few suggestions based on his experience with auto engine parts. You could probably find it here on Stunt Hanger. If I recall correctly, he was steering guys away from Oilite or porous bronze materials.

Divot McSlow

(edit: corrected Bob's name.)
Title: Re: Cox.049 Piston lapping
Post by: Fredvon4 on May 08, 2019, 10:08:34 AM
If you all insist on lapping, sanding, and grinding on Cox crank cases you should bite the bullet and create $50 hard anodising bucket..... Biggest expense is the H2SO4 solution

Hint if you suspect the crank journal of the CC bore is worn... you can bath and desmut the CC and re anodise and close the clearance up some.... also take and grade ALL your cranks....DIAMETER and LENGTH-----over the years the machining got sloppy and sloppier... early day Cox hired many folks to hand fit every engine out the door....ESTES did NOT do this

Barrels and barrels of Factory mass produced parts were produced...some percent of all the parts ended in reject bins over the years.... A few folks bought up all the stock...ALL of it...thunk on that a bit

I diamond Polish EVERY crank shaft I own....mostly because many times the running clearance is too tight and I do NOT want to ream the anodising off the bore   ( BTW if you want to greatly reduce the run in time on a Norvel .049 .061 Aero Engine...the Cranks are notoriously too large and drag a LOT!)

A set of small tubes of diamond paste is not very expensive..Light felt cloth, drill motor capture the knurled end, medium speed...mirror polish in under 15 minutes...Hot soap and water then carb cleaner clean

Shop around, mine 3 years ago were not $30...more like $16 + free ship as I recall

https://www.amazon.com/DMT-DPK-Dia-Paste-Diamond-Compound/dp/B000MF7JSO/ref=pd_day0_hl_469_5/138-7346822-9518445?_encoding=UTF8&pd_rd_i=B000MF7JSO&pd_rd_r=7299511f-71aa-11e9-bc3b-5ffc0e2db024&pd_rd_w=FttPE&pd_rd_wg=6ZB9Y&pf_rd_p=ad07871c-e646-4161-82c7-5ed0d4c85b07&pf_rd_r=GJHYTEBTRH5P806R2GA4&psc=1&refRID=GJHYTEBTRH5P806R2GA4
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 08, 2019, 11:57:21 AM
So have you been anodizing your Cox cases, Fred?

Divot
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 08, 2019, 08:11:14 PM
Sweet!

You are doing a lot of cool stuff, Juan!

I don't recall hearing of anyone experimenting with Turbo plugs in a Cox. (Possibly Les Akre, of the Canadian Racing Contingent?)  I would think you would want the hottest plug you could get. (That is just a guess.)  So something like an OS P3 or P4, maybe. How did you machine the seat for the plug? With the centerdrill? The critical thing with the Nelson or the turbo plugs is to eliminate any airgaps from the fit/threads. Else, you lose performance. Which is one reason why every head that fits a standard glow plug performs worse than a Cox glow head. If the cavity in the turbo plug is too big, it will also change the performance. I have never looked at these side-by-side, so I don't know how they compare.

With your lathe, you can also buy/make a spring-loaded guide that you can chuck in the tailstock. It has a point on it that will engage in the back of a standard tap handle. That guarantees that the thread centerline is perpendicular to your workpiece. What you show looks like a rigid setup, which may cause some issues if the runout is very large. Starting a thread with a bottom tap looks like an interesting experience....

I look forward to reports on your work on the bushed cases. When I get a chance, I need to figure out how to do a bunch of those myself. There has been a bit of discussion about the best material type(s) for the bush. Bob Zambelli provided a few suggestions based on his experience with auto engine parts. You could probably find it here on Stunt Hanger. If I recall correctly, he was steering guys away from Oilite or porous bronze materials.

Divot McSlow

(edit: corrected Bob's name.)

    Hello Dave
                         I have been aware of the Cox head mod for many years but had not done one. I found a thread on RC groups and read about it.  I`m posting a link to the thread. Turbo plugs will improve performance on our little engines and are plentiful in a broad amount of heat ranges. I know they perform well from a rework I did in 2015  on a Fuji.05 I got from Mecoa, I had the engine running at close to 27k rpm with open exhaust no pipe. Of course I did more things than just make a turbo head button. It is a screamer and I still have it. I stop working on it and moved on to something else. I received today a .2170 reamer and will be thinking how I will rework the reedy crankcase to install a bronze bushing. On cutting threads using a tap handle I don`t have a tap handle for that size of tap. I did most of the work on the glow head using a cox cylinder that I had turned down all the fins. I used the centering bit with a stop to drill first to make the seat for the plug and then I used a .275 drill bit to bore the hole but not all the way that might ruin the seat area for the glow plug then I used the M8 x 0.75 metric tap to cut the threads. Took the glow head out and noticed the snout was not flush with the chamber cut about .020 more with the centering bit and also had to make the threads a little deeper and now the snout of the plug is flush with the chamber and it seals well.
                                                                                                                                                                   Juan

http://www.rcuniverse.com/forum/1-2-1-8-airplanes-70/4533758-turbo-plugs-how-3.html
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 08, 2019, 08:29:50 PM
Juan, Do both heads have the same shape, compression ratio and plug depth? Also, if you're getting 20k+ from a Cox reed I wouldn't mess with it too much because, that's pretty good. Is your crankcase fully bushed because the aluminum will gall just behind the prop washer. It should at least have an oilite bronze nose bushing when you start to get up to those speeds.

Motorman 8)

 hello Motorman
                               Both heads differ,The cox with the turbo plug has a conical chamber that is bigger than the Galbreath/Nelson head chamber, Also the Galbreath head has a squish band that pushes the mixture into a smaller chamber. Plug depth compression ratio is not the same as you can observe in this photos.
                                                                                                                                                                           Juan
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 08, 2019, 08:43:22 PM
Juan,

It was lucky that the standard centerdrill matched the plug taper and the minimum thread diameter. That is what surprised me. If you have the plug seated hard against the tapered seat, you can't do better than that!

Your pictures showed a 3-jaw chuck on your lathe. To use that, I would grab the front of the case and cut in thru the back. Do you have a test indicator? If you do, you can fit a drill blank into the existing crank hole and let it extend out and run your indicator against that. Then bump the case in the chuck until it runs true. The only hard part there is finding a snug fit pin. Of course, with this approach, you are going to have to run a bush the full length. I don't consider that a disadvantage at all. And you can prep the aft end of the bush with the thrust bearing face and oil grooves.

If you have a 4-jaw chuck, then you could grab the back of the case and go in thru the front. With a 4-jaw, you would definitely need to indicate on the case, but you can do it without the close fit pin by just touching the OD of the front end, and follow up by touching the bore to make sure they are concentric. With this method, you could just bore for a

Do you have a small (actually, tiny) boring bar? A holder? You can make one pretty easy if you wanted to. I would start with an 1/8 HSS drill blank and grind the tip to shape. I have actually used piano wire for a temporary cutter in a pinch. With the boring bar, you are not limited to what the reamer will do. You can adjust your bushing press fit into the case, in other words.

I suppose most guys (and most shops, too) work with the tooling that they have. It will define your possible methods. Not always the best method, but one that is possible. Instead of just dreaming about getting it done. Like me.
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 08, 2019, 08:47:45 PM
If you all insist on lapping, sanding, and grinding on Cox crank cases you should bite the bullet and create $50 hard anodising bucket..... Biggest expense is the H2SO4 solution

Hint if you suspect the crank journal of the CC bore is worn... you can bath and desmut the CC and re anodise and close the clearance up some.... also take and grade ALL your cranks....DIAMETER and LENGTH-----over the years the machining got sloppy and sloppier... early day Cox hired many folks to hand fit every engine out the door....ESTES did NOT do this

Barrels and barrels of Factory mass produced parts were produced...some percent of all the parts ended in reject bins over the years.... A few folks bought up all the stock...ALL of it...thunk on that a bit

I diamond Polish EVERY crank shaft I own....mostly because many times the running clearance is too tight and I do NOT want to ream the anodising off the bore   ( BTW if you want to greatly reduce the run in time on a Norvel .049 .061 Aero Engine...the Cranks are notoriously too large and drag a LOT!)

A set of small tubes of diamond paste is not very expensive..Light felt cloth, drill motor capture the knurled end, medium speed...mirror polish in under 15 minutes...Hot soap and water then carb cleaner clean

Shop around, mine 3 years ago were not $30...more like $16 + free ship as I recall

https://www.amazon.com/DMT-DPK-Dia-Paste-Diamond-Compound/dp/B000MF7JSO/ref=pd_day0_hl_469_5/138-7346822-9518445?_encoding=UTF8&pd_rd_i=B000MF7JSO&pd_rd_r=7299511f-71aa-11e9-bc3b-5ffc0e2db024&pd_rd_w=FttPE&pd_rd_wg=6ZB9Y&pf_rd_p=ad07871c-e646-4161-82c7-5ed0d4c85b07&pf_rd_r=GJHYTEBTRH5P806R2GA4&psc=1&refRID=GJHYTEBTRH5P806R2GA4

          Hello Fred
                               I saved your advice, I would like to learn how to anodize and will do a search later on to find more info. I`m using old Black Widow crankcases because they have anodizing in the crank bore. I noticed how new parts fit is not the best. I will buy old engines that look to be in good shape for parts. I do have a small collection of new and old engines and will search for parts to use and play with. Thank for the advice.
                                                                                                                                                                                     Juan
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 08, 2019, 08:50:30 PM
Here is one reference from Bob Zambelli:  https://stunthanger.com/smf/open-forum/nobler-history/msg537455/#msg537455


  "We were working together to develop some new front bushings for the Fox stunt and combat engines. After many trials, I settled on a bushing grade manganese bronze, formulated for high-speed sliding applications."

And another:   https://stunthanger.com/smf/engine-set-up-tips/os20fp-crank-bearings/msg474567/#msg474567

   This one has photos that are interesting.

Can't find the one that listed the auto part number and specific material.

The McMaster Carr catalog lists quite a few different choices:  https://www.mcmaster.com/standard-bronze-alloys

   The Ampco 18 looks pretty good.  Hardness B90    Yield 37ksi

   544 Phosphor bronze                    Hardness  N/A   Yield 50ksi

   863 Manganese bronze                 Hardness B95    Yield 62ksi

   792 Leaded bronze                       I didn't see this in the catalog, but it might also be a good choice
   
Title: Re: Cox.049 Piston lapping
Post by: Fredvon4 on May 09, 2019, 11:10:05 AM
Cox International has over 300 NEW Cox Crank Cases WITH crank shaft and drive plate for $13 (+ shipping)

Refurbing some obscure Cox engine from your youth or some unique engine may be worth the effort to YOU

I decided after research to NOT fuss with secondary Hard Anodising mostly because I only had three worn CCs and the cost each was excessive compared to just buying a lot of "LOT"s and a Few Brand New from Bernie or Matt....many of my TeeDees (9) are 100% parts made (( they cost about $109 each))

E-Bay and RCG always has "LOT"s of 3 to 50 engines where the cost per engine is under $10//// big plus is a LOT of them have real metal back plates ( I hate the plastic ones)

very small set up for Aluminum Hard Anodising is easy to research and there are a number of sites selling turn key kits... (waste of $$$ IMO) the Anodes are likely already in your kit... H2SO4 battery acid is probably easy to get at many auto parts stores ....my concern was what to do with the acid month or years between use

I am more and more interested now in the various ways to anodise and COLOR engine parts...another thread discussion I am sure....there are some guys Like Valentine who make real pretty Co engines

I personally own EVERY Cox International Specialty engine.....each one serial number and unique selection of parts and colors

Rebushing a cox crankcase for you hobby enjoyment and fun is just fine with me....frugal fred, with NO mill or Lathe will set back and be in awe of your perseverance to take a $9.99 part and make it cost over $30 with little to no performance gain....yes a bit snarky.... sorry...carry on
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 09, 2019, 04:29:10 PM
Getting good chuckles, here, Freddo.

You have over $1,000 in Tee Dees built from parts and "EVERY specialty engine" put out by Cox International, but you're telling us we are ill-advised to spend a few bucks bushing worn crankcases on a reedy?

I can tell you from much Mouse racing, that reedy cases are soft. That the coatings used were not all equal. And that I have a box of them that have excessive wear on the ID. On the other hand, of the two(?) cases that I have that are bronze bushed, I have raced them hard and they still have a proper fit. So that would be evidence to me that there is a performance gain--you don't seize your engine partway thru a race from improper fit, and you don't blow a crank because of excessive wobble.

I applaud your Cox collections and your pride of ownership. But no real need for you to be, as you say, "snarky" over a guy doing his own engine repairs and performance development.

Dave

Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 09, 2019, 07:08:48 PM
Cox International has over 300 NEW Cox Crank Cases WITH crank shaft and drive plate for $13 (+ shipping)

Refurbing some obscure Cox engine from your youth or some unique engine may be worth the effort to YOU

I decided after research to NOT fuss with secondary Hard Anodising mostly because I only had three worn CCs and the cost each was excessive compared to just buying a lot of "LOT"s and a Few Brand New from Bernie or Matt....many of my TeeDees (9) are 100% parts made (( they cost about $109 each))

E-Bay and RCG always has "LOT"s of 3 to 50 engines where the cost per engine is under $10//// big plus is a LOT of them have real metal back plates ( I hate the plastic ones)

very small set up for Aluminum Hard Anodising is easy to research and there are a number of sites selling turn key kits... (waste of $$$ IMO) the Anodes are likely already in your kit... H2SO4 battery acid is probably easy to get at many auto parts stores ....my concern was what to do with the acid month or years between use

I am more and more interested now in the various ways to anodise and COLOR engine parts...another thread discussion I am sure....there are some guys Like Valentine who make real pretty Co engines

I personally own EVERY Cox International Specialty engine.....each one serial number and unique selection of parts and colors

Rebushing a cox crankcase for you hobby enjoyment and fun is just fine with me....frugal fred, with NO mill or Lathe will set back and be in awe of your perseverance to take a $9.99 part and make it cost over $30 with little to no performance gain....yes a bit snarky.... sorry...carry on

Hello Fred
                       I`m sorry you felt that your suggestion about anodizing was not appreciated. I have seen your work in the CEF. The Tee Dee .049 you posted for the engine of the month looked great. I noticed it had a Merlin glow plug/head, red anodized Spinner from Valentine and a Red Venturi,backplate, drive plate and Collect that I think you did. Also noticed the Cox Speed pan,Custom kraftsmanship NV assy.
                      In the past I have thought about anodizing a few heads but getting a kit for anodizing is kind of expensive because to receive chemicals that might be hazardous from the US will entail paying haz mat shipping. I tried to send two quarts of non tautening dope at one time and the cost would have been $175.00. So now I have run out of dope and use automotive finishes on my models.
                       I will try doing the bushing for my .049 reedy and if successful I will fix other engines that I have like a Fox.35 and a K&B .09.
                                                                                                                                                                           Juan

PS.  Is more than $30.  I just bought a few carbide tooling bits for the lathe and spent $33.95 and also cut a finger.
Title: Re: Cox.049 Piston lapping
Post by: RknRusty on May 09, 2019, 07:17:11 PM
Juan, I had to skip the last few replies except for Dave and Fred's last exchange, Lol. So I hope I am not re-posting an answer... Regarding the black oil when running it up to full song, be sure you didn't miss something as head-slapping simple as the drive plate contacting the starter spring. That makes scary looking effluent but is mostly harmless other than the drag. You are obviously a smart engine guy, so don't take offense at my simple suggestion if you've already thought of it.
Rusty
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 09, 2019, 07:27:25 PM
Here is one reference from Bob Zambelli:  https://stunthanger.com/smf/open-forum/nobler-history/msg537455/#msg537455


  "We were working together to develop some new front bushings for the Fox stunt and combat engines. After many trials, I settled on a bushing grade manganese bronze, formulated for high-speed sliding applications."

And another:   https://stunthanger.com/smf/engine-set-up-tips/os20fp-crank-bearings/msg474567/#msg474567

   This one has photos that are interesting.

Can't find the one that listed the auto part number and specific material.

The McMaster Carr catalog lists quite a few different choices:  https://www.mcmaster.com/standard-bronze-alloys

   The Ampco 18 looks pretty good.  Hardness B90    Yield 37ksi

   544 Phosphor bronze                    Hardness  N/A   Yield 50ksi

   863 Manganese bronze                 Hardness B95    Yield 62ksi

   792 Leaded bronze                       I didn't see this in the catalog, but it might also be a good choice
 

      Hello Dave
                             I don`t know what kind of bronze my machinist friend gave me but if successful I have some Ampco 45 valve guides that I bought for my 1967 Triumph Motorcycle that I might use in other engines I have. i have been working on a fixture to hold the crankcase while I bore. I will be using my 3 jaw self centering chuck on the lathe and will use a dial indicator to make sure (hope) that I get it straight. Found a P4 turbo plug that I will try later on to see how the reedy reacts.
                                                                                                                                                   Juan
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 09, 2019, 07:30:46 PM
Juan, I had to skip the last few replies except for Dave and Fred's last exchange, Lol. So I hope I am not re-posting an answer... Regarding the black oil when running it up to full song, be sure you didn't miss something as head-slapping simple as the drive plate contacting the starter spring. That makes scary looking effluent but is mostly harmless other than the drag. You are obviously a smart engine guy, so don't take offense at my simple suggestion if you've already thought of it.
Rusty

                Hello Rusty
                                       I have not thought about it,will check in the next runs.Thanks.
                                                                                                                                                                                       Juan
Title: Re: Cox.049 Piston lapping
Post by: Fredvon4 on May 10, 2019, 08:43:43 AM
I was trying to be a bit tongue in cheek  but my writing skills-- with a bit of irony and humor-- did not convey properly.... all the receivers read correctly the sender (me) was inept

I have worked up only one bronze BUSHED Cox .049 ....but my experience is purely anecdotal and since I only bench ran it ---not a good data set to form what sounded like to you guys a disparaging opinion....

Any way my poor writing aside , I think all hobby tinkering usually is a labor of love and fun...as noted my poor economy assertions compared to my obvious excess spending on things is indeed a tad hypocritical

But that is me.... super frugal some days and buying spree the next.

Juan.... I think you are in Puerto Rico... I have to believe somewhere on that Island is a shop that puts Lead Acid Batteries into USE....they are shipped over dry so somebody has drums and drums of Battery acid...... You will need a way to safely* store it ....For anodising it seems the Battery acid is good for a very long time IF you clean and de smut the aluminum part AND the Anode every use

* H2SO4...Sulfuric acid is obviously a caustic acid... it stores only in glass or Plastic containers. Must be tightly sealed and should not be near any metals or electronics....the vapors and fumes get deep into wiring and such.....

Hint...Most motorcycle batteries mail ordered will come in a box dry with a small plastic container of acid for the end used to install

Chem class 8th grade: Little Johnny took a drink, but he will drink no more, for what he thought was H20, was H2SO4
Title: Re: Cox.049 Piston lapping
Post by: RknRusty on May 10, 2019, 11:38:28 AM
Chem class 8th grade: Little Johnny took a drink, but he will drink no more, for what he thought was H20, was H2SO4
UUUUuugg, Fred, that made my stomach hurt. Now I need a whole bottle of Tums.
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 13, 2019, 09:58:17 PM
Hello guys
                         I made the fixture to drill and bore mi crankcases for a bronze bushing. I left unfinished the stub that was going to locate the back of the cases until I had it tight in the chuck of my sherline lathe. I cut the stub until I could slide the case on it. Before I did that I removed the edges under the aft portion of the cylinder hole otherwise the case would not slide in the stub of the fixture. after doing that I placed the first case on the stub and clamped it down with the aluminum washer and the four 4-40 screws using a dial indicator to zero the nose of the case. I got the screws snug and watching the indicator I tightened enough to keep the case in position.  Then I used a drill bit to enlarge the hole to.275 inch then I used a modified boring bar in the lathe and bore the hole to .300 inch.   I made a bronze bushing on my other hobby lathe and reamed it to .2170 inch size. I placed in the freezer and started work on a depth stop to screw to the back of the case to locate the bushing on the case since I was going to use a vise to press the bushing in. I measured 5 different cases and got 5 different measurements. I had measured the case and the distance from the back to the bearing area was.523 inch. I made the stub .518 inch because I could dress the bushing if the crankshaft needed to be farther forward avoiding having to remove the bushing if it came short and the crank to far forward. After pressing the bushing I reamed it again since after pressing it in the crank would not go in as before I pressed it. I polished the inside of the bushing and the crank turns freely. I will be assembling a motor to run the case and see how is working taking it apart and removing the crank to check for overheating. Here are some pics.
                                                                                                                                                                              Juan
Title: Re: Cox.049 Piston lapping
Post by: RknRusty on May 13, 2019, 10:52:22 PM
Nice work, Juan.
Forgive my ignorance of metallurgy, but will you pre-soak the bronze with some type of oil before assembly? Like, for lack of a better term, "priming" the bushing? Bronze is porous isn't it?

Rusty
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 14, 2019, 12:51:06 AM
Really nice, Juan!

Looks like the thrust bearing in the original case almost completely cleaned up when you bored the case to .300". Maybe a bit of a deburr and you were ready for a press?

There are formulas for the usual shrinkage you get when pressing a bushing, but it is easier when you're just making one to ream it again....

Not all bronze is porous, Rusty. You are thinking of sintered bronze, which they use probably use a fairly coarse powder.* They grind the powder, then compact it to shape in a mold. This makes a "green" part, then they sinter it. This would be the one-off method. They probably have a very automated method--perhaps even a continuous process method--for production parts. Because of all the (intentional) porosity, you can, just as you suggested, impregnate it with oil. So you get a bushing with a built-in oil reservoir. This type of bronze would not be my first choice for a high speed bearing journal. And since the engine gets continuous lubrication, the Oilite approach might hurt you more than help you.

Did you cut an oiling groove into the top of your journal after you got it pressed in, Juan?

Dave

*--If you look at the metal filter clunk for your fuel jug--I think sold by DuBro?--it is made of sintered bronze. The material is so coarse that the fuel goes right thru it. But the grass leaves, twigs, crawly bugs and whatever else might get into your jug won't.
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 14, 2019, 09:11:49 PM
Nice work, Juan.
Forgive my ignorance of metallurgy, but will you pre-soak the bronze with some type of oil before assembly? Like, for lack of a better term, "priming" the bushing? Bronze is porous isn't it?

Rusty

      Hello Rusty
                            I will forgive you if you forgive me. I`m going by what my machinist buddy gave me,he said it was bushing material and gave it to me free. I didn`t ask what kind it was but I will find out if it wears out quickly. Maybe later I might order some phosphor bronze from Macmaster-Carr. I do have some permanently lubricated bronze but I just remembered it now. I tried to machine it and I didn`t do good,maybe I should try it again.
                                                                                                                                                                                                     Juan
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 14, 2019, 09:35:48 PM
Really nice, Juan!

Looks like the thrust bearing in the original case almost completely cleaned up when you bored the case to .300". Maybe a bit of a deburr and you were ready for a press?

There are formulas for the usual shrinkage you get when pressing a bushing, but it is easier when you're just making one to ream it again....

Not all bronze is porous, Rusty. You are thinking of sintered bronze, which they use probably use a fairly coarse powder.* They grind the powder, then compact it to shape in a mold. This makes a "green" part, then they sinter it. This would be the one-off method. They probably have a very automated method--perhaps even a continuous process method--for production parts. Because of all the (intentional) porosity, you can, just as you suggested, impregnate it with oil. So you get a bushing with a built-in oil reservoir. This type of bronze would not be my first choice for a high speed bearing journal. And since the engine gets continuous lubrication, the Oilite approach might hurt you more than help you.

Did you cut an oiling groove into the top of your journal after you got it pressed in, Juan?

Dave

*--If you look at the metal filter clunk for your fuel jug--I think sold by DuBro?--it is made of sintered bronze. The material is so coarse that the fuel goes right thru it. But the grass leaves, twigs, crawly bugs and whatever else might get into your jug won't.

Hello Dave
                             I realized I had left a lip on the first case I made. For the next ones I remembered and cleaned the area in the lathe. I have done two more,Now that I have the fixture on the lathe is the time to do all I want because if I remove it I will have to realign it again. After I reamed the cases I slid a one of the high performance cranks and it would spin real easy dry. The reamer I used .2170 inch won`t allow enough clearance for the stock factory cranks. For those a bigger reamer must be used. The stop I made for setting the bushing has worked real good. I just press them in the vise and had no clearance problem. I have not machined a groove for oiling in the bushing. I know I will need it for high RPM engines that is why I mentioned overheating in a previous post also I don`t have a tool to make the groove might have to use a jewelers file. I made a small chamfer on the bushing where it faces the crankshaft to allow the fuel/oil to enter the bushing Here are a few pics.
                                                                                                                                                                                                  Juan
     
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 15, 2019, 03:39:51 AM
Looks really good from the pictures.

Just wanted to confirm we are talking about the same thing when discussing the oil grooves cut into the journal. There should be at least one (the stock cases had two at 180 degrees) on the face of the thrust bearing. Cut these before pressing in the bearing. There is also an axial groove. The cases I have seen have this groove in various different positions. It should be somewhere from 90 degrees before BDC to maybe 120 degrees before BDC. You want the shaft to be "climbing up" on the cushion of oil.

One way to make these would be to make a steel mandrel (dummy crank) and groove it. Then clamp it into the case and drill a small hole right down the airgap so that half of the drilled hole is in the mandrel and half in the case. The diameter should probably be around .025" by guessing. Set your quill depth to avoid breaking thru the front of the case. Done! Other alternatives would be to broach it, if you can make a broach.

If the bore was bigger and not such a high aspect ratio, you could use a handheld gouge. This was done all the time on babbit bearings. I will find and attach a link to a video that shows old time babbit bearing fabrication.

Dave
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 15, 2019, 07:41:08 PM
 Hello Dave
                       Your last post is of great help. we are on the same page about the lubrication groove. I made a tool to do as you suggested. I used a grade 5 bolt for the tool, I erased all the markings in the head and turned round. Since I knew the Id of the bushing is .217 inch measuring from a small dimple I made at the center of the head I drilled a .047 inch hole at a distance of .1085 inch then I turned the shank to .2165 and half the hole was removed leaving a channel to guide the drill bit in  making the lubricating groove. I have not decided in which side of the case I will be grooving. The smallest drill bit I have is .040 inch and will try that to see how it works. Thanks for your help. Here are pics.
                                                                                                                                                                                                    Juan
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 15, 2019, 08:56:19 PM
Sweet job, Juan!

You could also cut a flat on the disk of the drill guide. Then screw in a sacrificial cylinder. Make the flat location such that the bottom of the cylinder just touches the flat. Now your drill guide will not rotate, and you do not have to worry (as much) about breaking the small drill.

You could also tap the shaft end of your tool so that you can lock it down on the case with a small screw and washer. Just like you were putting a stud into the end of the stock crankshaft.

I think a .040" drill would probably work.

I would line up the axial oil groove inside the journal with one of the two radial grooves you need in the thrust bearing. That way, there is a clear path thru the thrust bearing contact area to feed the journal bearing. As far as I am concerned, that is a design flaw in the basic Cox engine. A shame, too because doing it right is not harder and it would not have cost more.

Divot McSlow
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 16, 2019, 09:58:05 AM
Hello Dave
                        I went out dining with my son last night and when I came back decided to do the oil groove on the crankcase. I drilled but did not go as far as I should have. This morning I decided to drill farther beyond the point I should have stopped to break in the tool. I the first photo it shows how far I got last night and the next this mornings work. I will be trying to buy a smaller drill bit to try it out in the other side of this crankcase as I might end up removing this bushing to examine it up close. Your suggestion worked real good. You didn`t noticed that on the first tool pics I posted the washer and screw. I had cut 4-40 threads on the tool and I made the tool a little short of the end so using the 4-40 bolt and a washer I was able to lock the tool in position. I think I should run the case to see how it performs before I continue experimenting.
                                                                                                                                                              Juan
Title: Re: Cox.049 Piston lapping
Post by: Dave Hull on May 16, 2019, 12:48:40 PM
Aaaah.  Sorry I did not fully understand your tool. You are way ahead of me. Very nice.

I agree with trying to make the groove smaller.

As far as the groove location, all the engineering books tell you approximately where it should go. Cox apparently either knew better, or didn't care at all. I have two cases in my hand right now. One is a cast case and the groove is about where you put yours. I have an extruded case from a product engine and the groove is about 60 degrees forward of the cylinder location. The groove in the cast case is slightly larger than the one in the extruded case. Both are smaller than your first groove. The Cox extruded case groove has machining marks that suggest that they broached the groove. The groove in the extruded case is parallel-sided. The cast case groove has some taper to it. It looks like the depth gets shallower the farther forward it goes.

I would try putting the groove about 45 to 90 degrees after (in crankshaft rotation direction) the cylinder attachment centerline. You want to feed oil into the bearing before the high pressure (load) area, which is going to be opposite the cylinder. (The bottom half of the case if the cylinder is up.) The idea is that the crank rides on a wedge of oil and does not touch metal to metal. If the groove is too big, or is in the wrong place it may act like an oil scraper.

Good progress, Juan. I am very interested to see how it runs.

Dave
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 16, 2019, 07:49:52 PM
Hello Dave
                       I finished 2 crankcases and proceeded to asemble an engine from parts I have,new galbreath/nelson head,new crankcase with bronze, old red backplate,hi perf crank  and an old number 5 cylinder and piston. The piston is so loose it comes out thru the top of the cylinder. I had tried to do the groove on the cases with a .020 inch drill bit my machinist friend gave me but it just didn`t work with the tool I made because the groove on the tool is .020 inch. The drill started to cut into the bronze but it followed the path of least resistance so it was back to using the .040 inch drill bit. I elected to drill the holes in the 7:30 to 8:00 hour location thinking that after ignition the conrod is pushing the crank to the right and down viewing the engine from the back backplate removed. I did a vertical slot on the middle top and bottom of the bushing.
                      I ran the engine on 25% VP nitro 20% Blendzall castor oil and 55% VP 1320 Methanol. The engine turned above 19,000 Rpm which surprised me because I was more interested in seeing how the oil would come out. It came out with no traces of metal wear as you can see in one of the photos it came out amber colored. In all I`m happy that I was able to do the mod correctly with a good result. I hope you guys enjoyed the Thread and the Pictures and that they might be of use to you.
                                                                                                                                                                                       Juan
Title: Re: Cox.049 Piston lapping
Post by: RknRusty on May 19, 2019, 01:47:34 PM
This has been a really fun thread. I admire the work you guys can do with metal.
Rusty
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 20, 2019, 07:02:51 PM
The bushed cases that KK did had two bushings. The case was bored from the front and they left the aluminum thrust face alone. The first bushing was much the same as you have done only shorter. The nose bushing was an oilite bronze bushing right off the shelf.

The oil groove can be made by grinding the end of a small triangular file flat and sharp then simply broaching the groove by hand. The oil groove is not needed because the clearance you want to spin that fast will let plenty of oil go forward. Also a big oil groove will trap oil and it will dry in there.

The other thing is to keep your bushing thin so heat can transfer to the aluminum. A good scheme is to press in a bushing with a smaller inside diameter then bore it out once it's in place. This way you can make it as thin as you like and it won't collapse when you press it in.

Motorman 8)


Hello Motorman
                                I used to read Joe Klause 1/2A column in Model Builder magazine and I still have those mags stored in plastic cases. I was not aware of many of the things he did,All I can remember was the NVA assy and if I remember well a Backplate mount  for Cox .049 TD. I would love to read those mags again. I collected mags for a long time and quit when they became catalogs. Is very interesting what he was doing when bushing the cases  he must had a good reason to do them that way. I have some prelubed bronze maybe I will try that some day. I made the bushings big thinking that I needed extra material to be able to do the oiling groove without the bushing collapsing on me. I could have made a smaller groove but I noticed that the newer crankcases have a big groove. I left a case with no groove and I assembled and engine but had two very short runs backwards which I stopped and then my battery for the glow plug died. I haven`t tried lately been spending time with my son and grandson.  Thanks for posting the information I saved it in my engine mods folder.
                                                                                                                                                                   Juan
Title: Re: Cox.049 Piston lapping
Post by: Juan Valentin on May 20, 2019, 07:14:03 PM
This has been a really fun thread. I admire the work you guys can do with metal.
Rusty

 Hello Rusty
                    I enjoy doing it and sharing it. That way I can collect information from other guys that have done similar work. I like to post photos because that way you guys can join me on my trip of what I`m doing. I have always heard that a picture is worth a thousand words. For me doing new things on my engines is OJT (on the job training) thanks for your kind words.
                                                                                                                                                                        Juan