Author Topic: Fox on the Run (Read 12495 times)

Motorman · « **on:** April 02, 2016, 07:05:50 PM »

Funny after 60 years in production they never made the motor mounts straight. Fixed that in one minute.

Drill all the way through the bushing

Lightly hone

You wouldn't believe how far out of square this was from the factory. I guess that's what makes one Fox better than another?

After boring, perfect fit for a SuperTiger G21 35 sleeve. Had to take a good bit off the top to get the exhaust to line up

That's right it's a hemi .010" deck. Head clamp made from stock head, sleeve is chrome plated too (by me!). Tiger sleeve fit right inside the Fox bolt pattern and 1/2" bolts were the perfect length, how did I get so lucky.

Stock appearing and ready for testing. The silver one has the (modified) factory parts with a custom high compression head and the rod is bronze bushed. The sleeve was chrome plated by Glen Dye. It turned 14.3 with the APC 8-8 tooth pick on a cold day with stock cylinder timing and very loose piston fit. I found a tighter sleeve and raised the exhaust in the middle and angled the transfer port up by the same amount. It still has the baffle.

The engine on the right is the Tiger Fox 33 I was building in the pics above (fox is shorter stroke than supertiger). The transfer passage is not wide enough for the porting and there's not enough metal to make it wider without having the cylinder burst off so, we'll see how it goes. the sleeve has the high nitro free flight exhaust port and it's been raised plus the stroke is shorter so it's probably got too much duration. I just want to see if it will run without bursting apart. Other than that the piston is 3 grams heavier and the conrod metal over the 5mm wrist pin is super thin so wish me luck on the test stand. I can say this, just poppin' it through it feels incredible.

MM

john e. holliday · « **Reply #1 on:** April 02, 2016, 10:05:43 PM »

Looks legal to me. Hope to see it at Brodaks.

Motorman · « **Reply #2 on:** April 03, 2016, 09:56:40 PM »

Testing went well today. Even though temp was 45 degrees both engines hit 14.8 with no parts failures. That's a 500 rpm improvement on a colder day so, happy about that.

The Tigerfox had a loose rod I just threw in it and it was turning the exhaust oil dark so, it's back in the shop for a high Zoot rod and additional mods now that I know it won't grenade. The silver fox ran so much better with the tighter piston fit and raised timing. I'll have to put a degree wheel on these things and see where they're at.

I installed a bronze bushing in the loose tigerfox rod

High Zoot rod in process

MM

Ken Burdick · « **Reply #3 on:** April 04, 2016, 10:25:03 AM »

pretty sweet project! It's amazing what lengths we'll go to. All of your work really reminds me of the progression of the Mk 111 engine to get it to run well......like re-machine "everything" Was there ever a question about tightening head bolts and discovering a bind?

Nice work!

Ken

Ken Burdick · « **Reply #4 on:** April 04, 2016, 10:34:33 AM »

BTW.
Don't forget one the reasons Luke Roy wanted to make their own crankcase....

Motorman · « **Reply #5 on:** April 04, 2016, 08:15:52 PM »

Rainy day, good day for engine work.

Checking the timing, exhaust 157, transfer 148, intake 35/40. The exhaust is a little high but it's a gabled port and I'm glad it has some blow down time as a stock superTiger don't. The intake closes too soon so I decided to cut the case for 35/60 and square off the round hole. Wish my camera did close ups because the intake looks wide open now.

I made this nifty tool to help scribe straight lines inside the crank bushing so I can mark out the intake port. It's just a half round rod the size of the shaft you use like a straight edge ruler.

I did port matching for the tiger sleeve the best I could with the thin metal case. Basically consisted of smoothing out all the flow paths, couldn't do any real shaping.

Cold weather all this week but bench testing will continue once the con rod is done. I think I'll also run my Tiger C35 plain bearing to compare.

MM

C.T. Schaefer · « **Reply #6 on:** April 05, 2016, 06:36:19 AM »

Walt, I's nice to see that you are 'on the job'. Interesting stuff! We have also been doing some moderate engine bashing and it has been fun so far. I built a K&B/ S-T combo for an antique proto ship that I restored. It runs but I haven't flown it yet. If you want to do some test flying during the week and need a circle, get in touch. There aren't many of us who care about this stuff! T

Paul Smith · « **Reply #7 on:** April 05, 2016, 06:57:44 AM »

You have a great machine shop. Your Tiger-Fox is a good example of putting whatever you can inside a Fox 35 Stunt.

Ken Burdick · « **Reply #8 on:** April 05, 2016, 09:25:46 AM »

Yah...a stunt-rattler.

Nice work

Motorman · « **Reply #9 on:** April 05, 2016, 09:39:28 AM »

Come to think of it this opens up the possibility of using the SuperTiger sleeve that has the baffled piston in the Fox 35 stunt. Didn't someone make an ABC version of that Tiger sleeve?

MM

Motorman · « **Reply #10 on:** April 08, 2016, 05:05:30 PM »

Ok, got the new rod done along with other mods and got out to test. First I ran a SuperTiger C35 plain bearing with the same prop/fuel/venturi and it peaked out at 15,000 rpm. Next was the TigerFox and it revved up to 15,150 rpm. So my dremmel tool work was worth another 300 rpm.

I only ran it enough to get a tach reading because I was getting black oil out the exhaust. Found the conrod was digging a trench in the backplate hey, that's got to be worth about 100 rpm right there.

Next mod is to get a hard back plate that has allot less clearance on the rod. Maybe make a steel backplate or maybe I can bolt a steel disk on the backplate. Also going to add a washer of some kind behind the drive washer to keep the shaft from moving in and out and now officially switching to the Nelson crank. The Nelson crank has a smaller hole and a weaker crank web so might go right back to Fox if it's slower or snaps off.

Still have to do vibration testing and finish reconbobulating the airframe.

MM

Richard Imhoff · « **Reply #11 on:** April 08, 2016, 08:54:02 PM »

Here's a K-Fox a stunt case with K&B 40 internals.

Yes it runs just fine a pulls a 9x7 at 13,500, have been doing some testing with it but it does have a slight vibration at low rpm. had to cut a bunch off the K&b 40 crank to get it in might change out the crank for a black head 35 crank and see if it helps a bit it will reduce the displacement a bit but who cares..

Have a couple of other 35's running with weird insides like a stunt piston and liner with the baffle cut off and a very high compression button head and it turns the test 8x8 at 14,3000.

Motorman · « **Reply #12 on:** April 08, 2016, 09:38:54 PM »

That's amazing. What did you cut off the crank to get it to fit? I know it's a 1/2" shaft did you turn that down or bore the bushing out? I'm impressed.

MM

C.T. Schaefer · « **Reply #13 on:** April 09, 2016, 06:11:48 AM »

Just as I figured. There are quite a few very clever guys out there who are interested enough to work on this stuff and let their imaginations run wild. I've been having lots of carefree fun till yesterday when my ALLFOX snapped a rod a little bit below the wrist pin. Tore up the piston and sleeve. Boo Hoo. Back to the cave.

Ken Burdick · « **Reply #14 on:** April 09, 2016, 08:11:46 AM »

Good idea! It hadn't occurred to me that there is no disp requirement.....love it

Richard Imhoff · « **Reply #15 on:** April 09, 2016, 01:35:42 PM »

yes the crank is 1/2 inch but there is room to bore the case to .500 but some times the stock bushing is cast off center then you have to bore it bigger and make a new bushing.
The crank pin on the K&B is pressed in so removing it and turning the crank counter weight to fit is an easy task. The old case is also opened up to fit the new sleeve and makes every thing straight unlike the stock case from the factory. If you notice there is no baffle on the piston it seems to run just as good with or without the baffle and making a head button is easier with out the baffle.
The o ring back plate is the easy way to go as it's just held in with the three screws and easy made step washers, the o.d is just made to clear the screw holes.

Motorman · « **Reply #16 on:** April 09, 2016, 09:29:45 PM »

Is the center of the crank pin aft of the center of the cylinder, did you thin the crank web down or something? The crank pin and rod are bigger diameter and the stroke is longer, did you bore the case out to get rod clearance?

I found out the K&B piston/ring/pin is lighter than the Fox piston/pin but has a similar pin height. If you use the fox crank it comes out to .385 displacement. The Fox conrod can be used by boring the wrist pin hole and K&B pin is smaller than the supertiger so, the fox rod should hold for bench testing at least. The next rod I make will be thicker with less clearance on the counter weight since we have report of stock part failure.

The next victim crankcase is in the crock pot right now.

MM

Richard Imhoff · « **Reply #17 on:** April 10, 2016, 05:22:10 PM »

Yes the crank web is machined thinner to get the crank pin in the center of the bore. All the K&B parts are used, the case was bored to fit the liner the case was also opened up a bit to fit the crank and the crank .o.d was turned down slighty, the K&B rod clears the case with out any mods to it at all.

Motorman · « **Reply #18 on:** April 12, 2016, 06:37:22 PM »

Thanks for the info Rich. I have allot of 4011 parts, I'll have to try something like that.

Next is my back plate evolution photo. From left to right 1)stock back plate, 2)Stock back plate with aluminum stuffer cap pressed on with glue and 3) a non-stuffer stock back plate with a polished alloy steel disk with 6-32 flathead and jbweld holding it on. I make the old style gaskets so the tabs don't bend. Initial testing showed the stuffer back plate to be slower than stock.

MM

Motorman · « **Reply #19 on:** May 09, 2016, 02:52:30 PM »

Well, I've had a bit of a set back. I have a high Zoot crank I was using and I've discovered that it turns into a wet noodle above a certain power level. The Zoot crank is a well made unit made from the toughest alloy that can be machined but, the Fox crank is made from high carbon steel then heat treated and is much harder than the Zoot crank. The Zoot crank is slower and is wearing hard on certain areas of the bushing and back plate. The engine is labored and draggy coming up to revs. You put the factory crank back in and the engine is just so crisp and free like it wants to rev. It's too bad because there's less vibration. It's a great sport/stunt crank which is what it was designed for but it's just not hard enough for what I'm doing in fox speed.

Of course the factory crank will spit out the front with this new build I'm working on so, what to do?

MM

Tim Wescott · « **Reply #20 on:** May 09, 2016, 03:11:39 PM »

Quote from: Motorman on May 09, 2016, 02:52:30 PM

Well, I've had a bit of a set back. I have a high Zoot crank I was using and I've discovered that it turns into a wet noodle above a certain power level. The Zoot crank is a well made unit made from the toughest alloy that can be machined but, the Fox crank is made from high carbon steel then heat treated and is much harder than the Zoot crank. The Zoot crank is slower and is wearing hard on certain areas of the bushing and back plate. The engine is labored and draggy coming up to revs. You put the factory crank back in and the engine is just so crisp and free like it wants to rev. It's too bad because there's less vibration. It's a great sport/stunt crank which is what it was designed for but it's just not hard enough for what I'm doing in fox speed.

Of course the factory crank will spit out the front with this new build I'm working on so, what to do?

MM

Uh -- AFAIK the modulus of elasticity of steel alloys are all pretty much the same. Making it "harder" just means you can push on it harder before it permanently deforms, not that it'll have a higher modulus.

If the Zoot crank has a bigger intake hole (even slightly bigger) that'd make the whole thing more flexible.

Or you went and bent your nice crank.

Make a crank out of some reasonable alloy and heat-treat? Or is that more than you want to do?

Or rework the Fox crank for better balance with a brass, lead, or tungsten plug.

Motorman · « **Reply #21 on:** May 09, 2016, 06:24:27 PM »

The hole in the zoot crank is bigger, it's not bent, all I know is the engine don't like it. The Fox crank is a ticking time bomb, I hope I'm not in front of it when it goes.

Looking at options like O-1 tool steel. I have a charcoal foundry to heat it but a little worried about warpage during quenching. It would allow me to make a slightly larger crank but, there's got to be an easier way.

MM

Tim Wescott · « **Reply #22 on:** May 09, 2016, 06:53:33 PM »

Quote from: Motorman on May 09, 2016, 06:24:27 PM

The hole in the zoot crank is bigger, it's not bent, all I know is the engine don't like it. The Fox crank is a ticking time bomb, I hope I'm not in front of it when it goes.

Looking at options like O-1 tool steel. I have a charcoal foundry to heat it but a little worried about warpage during quenching. It would allow me to make a slightly larger crank but, there's got to be an easier way.

MM

Do you have a tool-post grinder? Make the crank a bit oversize in the shaft and pin, temper, draw, then grind it to final dimensions.

I fully understand your concern about warping. I don't do as much machining as you, so it's all just voodoo to me.

Motorman · « **Reply #23 on:** May 13, 2016, 06:50:28 PM »

Anyway, continuing on with crankcase strengthening. Here is a music wire rod being glued to each side of the bypass. The lowest cooling fin has a small hole drilled in it to allow the wire to go up into the cylinder area and the wire goes as far down as it can. Still thinking of a way to brace under the exhaust port area.

MM

Motorman · « **Reply #24 on:** May 23, 2016, 05:41:37 PM »

Here's the new KFox40 ready for pipe length testing. Head was made from 2024-T351 billet. I made a special fly cutter to closely match the contour of the baffle so I could make a high compression head insert. Conrod was made extra thick out of 7075-T651 and had to shave a little off the Nelson crank balance weight to get clearance. Cylinder porting is a standard but I have some experiments ready on another piston/liner assembly.

Here's my solution for bracing the exhaust side. Piece is a block of aluminum shaped to fit the side of the case and JB weld.

I passed the mile stone of 16K with the new engine but I expected more. The small shaft on sport engines like this always seem to hold them back so the new shaft is in process and will be a bit bigger, stronger and balance better. Shown here with a factory crank.

Got a 1-1/2" Chinese "Miracle" spinner off eBay. I'd recommend the 1-3/4" as mine needed allot of machine work to fit the APC 8-8. Engine on the plane is the TigerFox which has also hit 16K. Can't put a pipe on that one so it might become obsolete soon.

MM

Motorman · « **Reply #25 on:** June 04, 2016, 01:07:32 PM »

Did an experiment. If you cut the baffle off a K&B 4011 piston and make a regular racing head, expect to lose 1000 rpm. In other words, it don't work. Just thought I'd save somebody some time and money.

MM

RandySmith · « **Reply #26 on:** June 29, 2016, 12:18:24 PM »

Quote from: Motorman on May 09, 2016, 02:52:30 PM

Well, I've had a bit of a set back. I have a high Zoot crank I was using and I've discovered that it turns into a wet noodle above a certain power level. The Zoot crank is a well made unit made from the toughest alloy that can be machined but, the Fox crank is made from high carbon steel then heat treated and is much harder than the Zoot crank. The Zoot crank is slower and is wearing hard on certain areas of the bushing and back plate. The engine is labored and draggy coming up to revs. You put the factory crank back in and the engine is just so crisp and free like it wants to rev. It's too bad because there's less vibration. It's a great sport/stunt crank which is what it was designed for but it's just not hard enough for what I'm doing in fox speed.

Of course the factory crank will spit out the front with this new build I'm working on so, what to do?

MM

Not a noodle... here are a few things you need to know about installing the HZ crank, first the crank does not have the "ditch" cut into it ,a s the FOX ones does as a shortcut to bypass making the bushing in the case clean at the back with a radius cut into it, this is also a WEAK point of the FOX Crank
The HZ crank install requires that you cut , or lap a " RADIUS " into the back edge of the crankcase bushing, part of normal install and is far superior to cutting a ditch in the crank.. IF you do not do this, the crank has a drag to it, and generates more heat drag, and pushes the crankpin back towards the backplate. And will rub on the backplate.
The HZ crank will NOT hit any FOX backplate if installed correctly
Second the FOX Rod should have vent holes cut into it for oiling, and the stock Fox rod has NO chamfer in it at the bottom front, The HZ cranks have a small perfect little radius made into it for strength, if you DO NOT cut a radius into the FOX rod, the rod will not seat all the way up on the crankpin, causing heat drag and pushing the rod farther back into the backplate, It will rub or dig into the backplate, this is very common in engines, and easily done It will NOT rub or dig into the backplate if installed properly
Next FOX bushings are all different sizes, so make sure you start with at least .001 clearance

The HZ crank test I have done all have been as much or most times MORE RPMs than stock cranks
THe HZ crank tested with my Rockwell diamond hardness tester shows a harder surface than stock cranks.
The HZ crank is made of steel and sent out and double Nitrated , very deep then ground to size

Putting the crank in using the correct blue printing techniques will result in a superior engine

Also all of my test never showed the stock backplate to give higher RPMs than the cnc one, the cnc one is not any faster but it does make the engine piston sleeve fit and rod last much longer

Also the ST G21-40 piston and sleeve will fit into the FOX 35 case, and it has a baffle and ring

Randy

Ken Burdick · « **Reply #27 on:** June 30, 2016, 09:30:59 AM »

Randy.
Can you recommend a good place for the nitrate treatment? I have a crank project that will need it.
What are the lot charges for your supplier?

Thanks.

Ken

Dan McEntee · « **Reply #28 on:** June 30, 2016, 06:42:47 PM »

Quote from: Ken Burdick on June 30, 2016, 09:30:59 AM

Randy.
Can you recommend a good place for the nitrate treatment? I have a crank project that will need it.
What are the lot charges for your supplier?

Thanks.

Ken

I went to work in the injection plastic molding business in the last year, and in learning about the mold and their repair, certain parts are nitride treated for surface hardness. You might want to investigate that path if there are any injection mold repair shops in your area. I was surprised to see just how much of a beating the molds get in the process and this is quite common in the repair and modification of molds.
Type at you later,
Dan McEntee

RandySmith · « **Reply #29 on:** June 30, 2016, 06:49:52 PM »

Quote from: Ken Burdick on June 30, 2016, 09:30:59 AM

Randy.
Can you recommend a good place for the nitrate treatment? I have a crank project that will need it.
What are the lot charges for your supplier?

Thanks.

Ken

Hi Ken
I will look to see if I find a shop that will do small runs

Randy

Ken Burdick · « **Reply #30 on:** July 02, 2016, 11:28:40 AM »

Thanks Randy.

Dan.
I spent many years dealing with molds and their maintence. It never ends. Plan to cycle molds out for at least a few weeks while they get rebuilt. ....man, what a pain that is. Glass filled nylon is worse.

Cheers.

K

Fredvon4 · « **Reply #31 on:** July 03, 2016, 11:16:43 AM »

I must say up front I was a simple enlisted Army mechanic with zero engineering degree or any other relevant schooling or back ground.

Along the way I wrote several product improvement suggestions ( Army Incentive Awards program) for several helicopter turbine engines or attached accessory drive components

Two of my proposals got me a temp duty trip to a Army depot and on to GE Dynamics where I got to meet with the scientists and engineers and learned a bit about their craft.

At the time I had read about new metal hardening methods, cryo, nitride, heat cycling, etc and asked a guy (I regarded as a genius in the area- he designed a lot of internals of turbine engines) why certain parts were not treated. He gave me a long complicated dissertation about the properties of some typical metals and why proper design and removal of all stress risers was preferable to hardening...from a cost per part point of view, total life time point of view, and reliability point of view...Then on to many of the parts that must be treated because the alloy was several orders of magnitude stronger or longer lived with the proper treatment ( he told me about crystalline structures and many other properties of some metal alloys)

One of the points he tried to get me to understand (we were discussing internal turbine engine parts)(( we had a rash of radial turbine compressor section explosions)) was that some forms of cryo/heat treating actually do not allow the metal part to properly expand at the operating temperature and loads as the original engineering spec required

As I think of this issue --2 cycle cranks breaking under certain conditions--- I wonder if it i just improper Alloy selection and machining. The parts I was helping to get better life and reliability spun over 100,000 RPM with radial loads in the tens of thousands FtLbs....

Seems to me a crank shaft for any under 40,000 RPM 2 cycle engine is well within the range of available machinable or forged alloy metals

Perhaps I should not poke around these subjects as I
A.) don't really know what I am talking about, and
B.) only now fly for fun and have no real need for the latest and greatest Hi Zoot parts

Once upon a time I desired to make my 80 CU In Harley Evo engine double the torque and HP....to that end I bought special machined HyperUtetic pistons, sent them one place for Ceramic dome coating and skirts coated with dry lube, then off to another place for total seal gap-less rings. A new set of Factory aluminum jugs had the iron liners removed by another cottage company, cryo treated, pressed back in and then perfectly honed/mated to the new pistons with proper plates for head torque pre-load

many other complimentary parts went in to the engine build, heads, cam, roller rockers, high zoot valvs and seals etc etc....

So $3500 later I had a out side looking 80 CI Harley engine that would stand up to a S&S 103CI engine and talk big chit...of course if you have $30,00~$50,000 you can get 800 to 1200 HP from this simple V twin engine

Thus I think a Fox .35 could actually be made (for the bucks) to spin over 20,000 RPM at 2+ HP reliably....but I certainly don't need to spend the $$$$ for one

Fun thread tho....perhaps a slight over drive gear head would be a better approach to eek out more speed

Motorman · « **Reply #32 on:** July 05, 2016, 04:59:28 PM »

You would think someone who can do the things shown in this thread would know how to put a crank in a 35 stunt.

HZ crank is a tremendous improvement for stunt/sport planes.

I have one factory crank that's faster than the HZ crank. When I took the HZ crank out the wear marks showed it had been flexing. Keep in mind this engine produces MUCH more power than the Fox 35 in your Nobler. I have since tried other factory cranks that were on par with the HZ crank.

My conclusion, the one factory crank I have is made well and has less flex than the HZ and so is faster. The other factory cranks I have are not made as well.

Tach don't lie.

MM

Ken Burdick · « **Reply #33 on:** July 06, 2016, 09:40:30 AM »

any Fox is an engine of infinite odd order variables.

Al Ferraro · « **Reply #34 on:** July 10, 2016, 10:30:36 AM »

(factory crank I have is made well and has less flex than the HZ and so is faster)
Walt, did you reset the head clearance after you installed the HZ crank? My HZ crank had a .009 shorter stroke than the stock crank and that much extra head clearance would cause a loss of power. I am running the HZ crank in my engine (retimed to my spec) and it spins up real nice with no vibes.
Al

Motorman · « **Reply #35 on:** July 10, 2016, 07:06:03 PM »

I actually have the HZ crank in the K&b Fox because I know it won't break.

MM