Fox 40 tuning for stunt

I thought as I have started taking the Lew Wollard tuned engine apart why not photo the bits and find out more about what can be done to make this engine good for stunt. I have never seen an un-modified version so I may attribute some things that are part of the original design but correct me if I am wrong. The mods that I can see so far are:-
[photo not recovered: shaft1.jpg]
The shaft seems to have been balanced by removing material from the crankpin area. It also looks to me as though some reshaping of the induction hole has been done.

[photo not recovered: liner1.jpg]
The shape looks a bit complex for a production engine so has it been modified?

[photo not recovered: cylinder_head.jpg]
This looks like a new special part. I guess that the head shape has been changed (has anyone got a picture of the standard item?)

[photo not recovered: head_fins.jpg]
This looks like the old head remachined to accept the new core head.

This is a replacement item. It looks a little loose and would benefit from a sealing ring. It is held in with 2 grub screws. The bore is 7.3mm (any comments on this size?)

I also found, when inspection the crankcase that some sort of glue - probably epoxy - had been put at the top of the transfer ports probably to lower them by about 1/16" (ish) The epoxy was quite soft from the action of the oil and some just fell out when I poked it with a cocktail stick.

Question should I replicate this epoxy with a better material? if so what?

Further work to be done:-

[photo not recovered: piston1.jpg]
There is some extra material in the castiron piston so I can probably take 10% more weight out of it if I am careful.

I will probably clean up some of the mods - smooth the grinding on the crankshaft - remake or modify the venturi to aid sealing - replace the epoxy in the transfer ports.

Regards

Mike

LAST EDITED ON Nov-06-04 AT 12:35 PM (CDT)
 
Mike,

Lew Woolard wrote a good article in STUNT NEWS several years ago on his mods to make the Silver Foxx out of the small-frame 40.

The thing he stressed, and probably DID, that isn't so noticeable with yours, is to thin the top flange from the UNDERSIDE. The cylinder slips deeper into the case, which 'lowers' the exhaust opening 'time' (in ºATDC, or measured in total EXHAUST OPEN time in shaftº). THEN the bypass and boost ports were RAISED and shaped as you show in the pix -- that's what he found worked better...

Why? The stock engine has an early-opening exhaust 'timing' for much higher RPM use. 'Lowering' the cylinder in the case delays the start of the exhaust period to where it is more suitable for the stunt RPM range. Turning down the flange thickness from from the under side achieves this lowering, but also slides the bypasses/boost down, and they also open later in the revolution. Grinding as shown raises the opening edges, for a longer open time, so a fuller charge goes upstairs to burn next time.

The numbers are pretty critical, and Lew has it right, sweet and reliable. (Example -- you don't want the bypasses open before the exhaust -- FIRE DOWN BELOW!! ...or too long afterwards, which reduces the time available to transfer fresh charge to the upper cylinder.)

BTW, You may be able to reduce vibration by extra care in balancing your props... Seems obvious, but still works.

LAST EDITED ON Nov-06-04 AT 12:42 PM (CDT)
 
Hi Mike,

A suggestion, for what it's worth: If Lew has done mods on this engine, I would try it out first before doing anything to it. Not to say that you can't do the mods, but it is a really sweet running 4-2 engine to begin with.

I say this because the one I run is completely stock. I have not found it to be any worse in the vibration department than most of the iron piston engines, and Lew has already done quite a bit of balancing to the one you have, and he has "hemied" the head. So it should be even better than my stock ones.

I run them in Classic ships where prop clearance can be a problem, and stock they swing 10" to 10 1/2 inch 3 blades (5 to 6 pitch) with NO problems on 5%-29% fuel.

Lou C. refers to a small case 40 (Lew's Silver Foxx) which is a
different animal as he he knows.

Bill <><

Right, Bill... I didn't spot it as the early-schneurle (rhymes!) beast...

Still, Lew has used the raised segment grinding on the bypasses on *both*, apparently. It may be to start flow in the desired direction at the desired time. A lead-in like that might not be certain if the bypass & boost edges opened "square"... Lew's method may be like putting a gentler opening ramp on a cam.

Stuffing the area below the cooling fin cuff 'deck' may also be to aim the charge flow. Odd that Duke may have preferred turbulence. Of course, turbulence could keep the charge atomized better. Still seems cleaner flow through a radiused port past something like Duro 600 epoxy-aluminum putty to speed it up may be better.

Is Duro 600 another EPA victim? Haven't seen or heard of it in years. In my experience, most 2-part epoxies will soften over time under heat and raw fuel exposure.

LAST EDITED ON Nov-06-04 AT 09:12 PM (CDT)
 
I'm confused. Is this an engine you've bought that was re-worked by Lew Woolard? If so, why are we showing his mods to the world? I'd like to know the mods, too, but sheesh - this doesn't seem fair.

On the other hand: bits of epoxy just falling out?

Someone please explain this to me. I don't get this post.

The ports in the liner are the stock configuration. The button head isn't stock; I'll take a picture of the orignal head and post it later this weekend.

The Fox 40 I have doesn't have any circular holes cut in the corners of the bypass ports. That must be a mod. The stock sleeve lip is about .1 in. You can check yours and see if it is thinned. At one time Fox sold the Mk IV with a thinner sleeve and a shim, so you could detune it yourself easily for slow combat. It think they used a .032 shim.

The shaft looks like it has the opening side cut a bit, maybe 5 deg. or so. That mod will often increase power.

The ring in the piston was left in on purpose to help keep the piston round during grinding. Be careful if you grind it out, the piston may distort.

Hi Phil (and others),
I think y'all missed the previous posts.

This is an old 1970's Fox 40 Stunt, big case that was orginally going to be Duke's Pylon engine.

These are the ones GMA redesigned for Duke to be stunt engines, and Lew W. has worked on this one.
It should be about as good as it gets after Lew tuned it.

Not a big back door Fox.

Bill <><

LAST EDITED ON Nov-07-04 AT 10:52 AM (CDT)
 
Yeah, I did mis-recogize the motor. The sleeve pic looked like a boost port at first glance. Sorry.
A full shot of the motor at the top would have helped. The interior parts, except for the sleeve, look like pretty generic Fox.

LAST EDITED ON Nov-07-04 AT 10:38 AM (CDT)
 
Closer inspection of the crankcase shows significant mods at the top. The top 1/4" of the 3 transfer passages have been filled with a grey filler (any offers as to what?). It looks to me as though the original engine had these passages open at the top and closed by the cylinder fins - at least that is the was way I would design it for easy diecasting. My earlier comments about epoxy in this area may be wrong, I have dugout the rest of the epoxy like stuff and I don't really know what it is it could even be a build up of thickened castor oil but it does feel like soft epoxy.

[photo not recovered: crankcase.jpg]

I must admit that I don't fully understand what the filling of the top of the transfer passages does. It doesn't alter the timing as that is controlled by the ports in the liner. It does fill the dead area of the passages and, in an inverted engine it would reduce the amount of fuel that could gather in this area. It also makes the sealing of the top of the passages more reliable as there is a bigger area for the gasket to sit on and probably smooths thaa gas flow into the cylinder.

Bill L Thanks for your comments I am pleased that this engine has potential. I was planning to reassemble the engine un-touched except for a clean and oil but if it does prove to have vibration issues I can see some more opportunities to reduce the reciprocating mass.

Regards

Mike

Hi Mike,
My guess, with out talking to Lew about it, would be to help the "Fox Burp" on outsides.
I tried mine on a profile, and had to raise the tank QUITE a bit to keep it from going too rich inverted.
No problems with an upright or inverted engine installation.
Bill <><

Here is the head picture I promised and some other shots. I've probably worked on 15 or so of these, UC and RC and all the heads (combustion chambers that is) seem the same, as well as the porting. As others have said, the button insert on your engine is not original.

Just for reference, these engines came out in 1971 and the first ones were matte finished and used phillips head hardware. Later engines were tumbled and had slotted head cylinder head screws. There were other variations, but mechanically the engines were all the same.

Oh yes, the cooling fins were an aluminum "Muff", snugly pressed over the liner.

In some of Duke's writings, he mentions letting the top of the exhaust port hang lower than the top of the bypass to create turbulence in the area; kind of anti what lots of guys do to streamline the flow of fuel up into the intake ports. I would guess that the rework on the top of the your case was an effort to streamline the flow to the intake ports.

Hope this helps!

[photo not recovered: 71fox40mon.jpg]

Hi Doc,
I had a "mell of a hess" trying to get that Rocket 35 to run. hahahahaha
Put a 35 stunt sleeve/piston in itand it's ok now.
Thanks for the pics. All of my '70s 40 Stunts have/had slotted screws. And my first one had rings machined around the outside of the head which was polished. A later replacement head was just plain and not polished. The one I use most had the venturi cut of by a buddy, and then I just stuck the venturi insert back in w/NVA. Works fine. Got one that has only been run once.... need to break it in!
Bill <><