News:


  • March 28, 2024, 11:47:51 AM

Login with username, password and session length

Author Topic: Cox.049 Piston lapping  (Read 6789 times)

Offline Juan Valentin

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 587
  • USAF 1969-73 ANG 73-77
Re: Cox.049 Piston lapping
« Reply #50 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

Offline Dave Hull

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1901
Re: Cox.049 Piston lapping
« Reply #51 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

Offline Juan Valentin

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 587
  • USAF 1969-73 ANG 73-77
Re: Cox.049 Piston lapping
« Reply #52 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

Offline RknRusty

  • 2019 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 2689
    • My Tube channel
Re: Cox.049 Piston lapping
« Reply #53 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
DON'T PANIC!
Rusty Knowlton
... and never Ever think about how good you are at something...
while you're doing it!

Jackson Flyers Association (a.k.a. The Wildcat Rangers(C/L))- Fort Jackson, SC
Metrolina Control Line Society (MCLS) - Huntersville, NC - The Carolina Gang
Congaree Flyers - Gaston, SC -  http://www.congareeflyer.com
www.coxengineforum.com

Offline Juan Valentin

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 587
  • USAF 1969-73 ANG 73-77
Re: Cox.049 Piston lapping
« Reply #54 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

Offline Juan Valentin

  • Trade Count: (0)
  • Captain
  • *****
  • Posts: 587
  • USAF 1969-73 ANG 73-77
Re: Cox.049 Piston lapping
« Reply #55 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


Advertise Here
Tags:
 


Advertise Here