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Old Aug 08, 2011, 05:06 PM
Bill Mohrbacher, MECA Fox Guy
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Beaver Falls, PA
Joined Dec 2006
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First Fox 29Rs

OK Twin Stack - Here is the article and comparison photos of the 1950 Fox 29 stunt and 29R I did for Engine Collectors Journal. You engine guys really need to join MECA and subscribe to ECJ; every issue has good stuff like this!

Some time ago, I borrowed 3 Fox factory experimental 19s. I built a rig where I could conveniently measure their port timings. While I had this rig set-up, I got to wondering about what had been done to the early 29 Racing Specials to make them worthy of that name. What I found is the basis of this article and can be summed up as A LOT!

The 1950 Fox 29 Stunt (29S), ECJ #7 is the 4 bolt head, 2 bolt rear cover, Permold 29. The 1950 Fox 29 Racing Special (29R), first advertised in the October 1950 Model Airplane News is externally almost the same engine. 29R is stamped on the front of the exhaust stack (very lightly on my example). The venturi throat has been enlarged. These are the visible differences. Oh yes, if you look into the exhaust stack, you can see the port is very high. The Austin Craft NVAs and the prop hardware are identical on the two engines.

But is that all you got for your extra dollar? The ad shows the 29 Stunt cost $11.95 while the 29 Racing Special cost $12.95 (interestingly, that $1 has grown to be worth $8.60 in 2007 dollars, geez the stunt 29 would only cost $103 today, a bargain). Well, you got more for your dollar as well see.

Removing the rear covers and the heads, they appear to be identical on the 29S and the 29R, allows the port timing to be measured. The timings for these engines are show on the drawing (thanks to Roger Schroeder for putting me on to DeltaCad). Here you can see the crankshaft, intake, and exhaust porting of the 29R all have longer durations and all open earlier and close later than the 29S. I should mention I measured things related to the front of the engine and used Before Top Dead Center, BTDC and After Top Dead Center, ATDC. Before I did this, I went through a fair number of engine test reports to see if there was some kind of standard, but I found some guys used ATDC while others used Before Bottom Dead Center. But who cares as long as we know how we are defining things? Besides this drawing, a table at the end compares any dimensions I measured.

Next we pull out all the guts and compare the cases. Take a look at the pictures. I mentioned the 29R and enlarged venturi before. The hole in the bushing at the bottom of the venturi has a rectangular shape on the 29R. Most surprisingly, the 29R bushing is some kind of ferrous material (meehanite?), not bronze like the 29S. The hole at bottom of the venturi proper does match the bushing. I would guess that the bushing had the hole finished and was then pressed into the case.

Move on to the crankshafts. The 29R has its web is cut away. This lightens the crankshaft. You can also see the 29Rs shaft intake has been opened up considerably by thinning clear to the edges of the port on all 4 sides. The bores are the same.

The 29Rs piston has been lightened by thinning the skirt and cutting away part of the inner belt at the wrist pin holes.

The liners hold a big surprise. You expect the ports to be bigger on the 29R, but look at the intake port of the 29R; it is the picture window intake found later on the 35 Series III Combat Specials. John Hall pointed this out earlier when I thought this actually originated on the Series III. Everything old is new again! Fox even used a Meehanite crank bushing on the bushed 36 FIRE engines in 1976.

A lot of folks see the picture window intake port and assume its purpose is to pass more fuel mixture, but as you can see in the photos with the piston in place, this isnt the case. The window is only about way open when the piston is at BDC. I would think the lowered hole allows easier gas passage for intake, kind of like rounding the edges of the intake. Maybe it also creates some turbulence. When the bottom of the piston opens the port there is a lot more area for the charge to enter the bypass, kind of like the holes drilled through the pistons and liners of the racing engines, McCoys and Doolings I think. Id love to hear from some other folks on this intake.

As far as I could tell, the compression is actually the same on both engines. This surprised me, but the head dimensions and any other dimension that would influence compression are nearly identical.

Well, there you have it. For $1 you got an engine where every significant part except the head and rear cover was handworker. Not a bad deal! Id like to know who did the early modifications; I think this was before George Moir was at Fox. If anyone has comments or corrections, Id like to hear them.

THAT'S ALL FOR TONIGHT
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Old Aug 08, 2011, 06:45 PM
Grumpa Tom
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Mr. Wiz, check this out.
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Old Aug 08, 2011, 06:47 PM
kill your idols
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Mr. Wiz, check this out.

nice custom powder job man. i love webras
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Old Aug 08, 2011, 07:53 PM
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What model Fox is this?

Jim
Jim, your FOX 29X is a little unusual in that it had a steel rotor disc. Nearly all other rear induction engines employed either an aluminum alloy or non-metallic disc, such as nylon or bakelite. Probable explanation being that the FOX was just too powerful & high revving for anything less than steel. BOB
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Old Aug 08, 2011, 08:01 PM
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Here is one for you fans of unusual Fox engines.
Engine Test reports on this brute can be found in Post #313 (early one) and #349 (later single plug model)
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Old Aug 08, 2011, 08:35 PM
Time for me to Fly...
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Mr. Wiz, check this out.
A blue T4-60 wow.... I wonder were I can get one of those? My wallet doesn't want to know but I do.
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Old Aug 08, 2011, 08:51 PM
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Reggy, Many Thanks for being brave enough to pull that Sidewinder apart, and taking such great photo's. To my knowledge, no-one else in the last 60 years has done what you have, so its truly historical from an engine collectors viewpoint. I have to admit though, that I will only pull an engine down as an absolute last resort, and here is an example. A few pages back, I posted some photo's of my Veco 35 R/C. Now, this engine was brand new and never run when I got it, but it was stuck hard. Looking in the exhaust port, I could see that the piston was nice & shiny, but the outside of the liner had light surface rust (this can just be seen in one of the photo's). I pulled the plug out and noted that the top of the piston (almost at T.D.C.) was also bright & shiny. Starting on the heat and acetone treatment to loosen it up, I noticed that this Veco was particularly stiff and difficult to turn. After many failed attempts to get the thing moving (not helped by the Veco prop driver not being positively keyed to the shaft) I was starting to get desperate. I was squirting WD-40 in, and heating the engine much more than usual, when eventually it "gave" and started to turn. Now I discovered the real problem - the piston had been (lightly) rusted to the cylinder walls ! I was now faced with a dilemma - I had already turned the engine over several times by this stage, not realising that rust was present in the cylinder. What to do ? Even if I stripped the engine right down now, the worst damage had probably already been done, so (keeping in mind that I got the engine pretty cheaply) I made the decision to continue with the engine in one piece, as a sort of experiment if you will. I began a process of squirting oil in the cylinder, turning a few times, then flushing the brown muck out with acetone. I guess I went through this cycle 10 or a dozen times before the oil started to become reasonably clear, so then I bolted a prop on and started flicking it over for 20 or so times, flushing and re-oiling. The engine now, as seen in the photo's, is as loose as a goose and flicks over beautifully with excellent compression. The piston itself is obviously made from harder material than the liner, as the piston looks like new whilst the liner has some visible vertical marks which must be only microscopically deep. The proof will be in the running of the thing, which I intend doing in a week or so, so stay tuned ! BOB
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Old Aug 08, 2011, 08:54 PM
Time for me to Fly...
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So I'm at our club's annual open house/air show and I brought along my OS K6 to some of the guys. They all looked at it and asked questions and the like. We ended up talking about old engines for several minutes. About an hour later one of the elder gentlemen presented be with a bag containing these two engines I've pictured below. He said I could have them as long as I promised not to ever sell them. That was an easy promise to make and it will be an easy one to keep too. Then I began to ask about them. The McCoy .36 is one he bought new as a kid.

The other is one his son bought from someone else a long time ago for ten cents and here is what he could tell me about it. He believes its a Mowhawk engine made in Herkimer NY. He also believes it's a first generation conversion of gas engine to glow because of the brass colored jacket around where the ignition parts would go. I've visually compared it my ignition OK .29 and I'd tend to agree with everything he said. I cant specifically tell if it's a .29 but it looks like it may be. Can anyone verify or correct anything I've said about it so far? Does anyone know where I might find a needle valve assembly for it?

Thanks in advance,
Wiz
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Old Aug 08, 2011, 09:10 PM
Time for me to Fly...
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Check out this 2cc inline 4 cylinger 4-cycle. Pretty cool, eh?
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Old Aug 08, 2011, 09:31 PM
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Check out this 2cc inline 4 cylinger 4-cycle. Pretty cool, eh?
That is superb Mr. Wiz - you know you want it ! BOB
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Old Aug 08, 2011, 09:32 PM
Time for me to Fly...
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That is superb Mr. Wiz - you know you want it ! BOB
Yea, well they want ice water in hell too but they ain't get it and neither am I.
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Old Aug 08, 2011, 09:39 PM
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The other is one his son bought from someone else a long time ago for ten cents and here is what he could tell me about it. He believes its a Mowhawk engine made in Herkimer NY. He also believes it's a first generation conversion of gas engine to glow because of the brass colored jacket around where the ignition parts would go. I've visually compared it my ignition OK .29 and I'd tend to agree with everything he said. I cant specifically tell if it's a .29 but it looks like it may be. Can anyone verify or correct anything I've said about it so far? Does anyone know where I might find a needle valve assembly for it?

Thanks in advance,
Wiz
According to the A.M.E.E. Wiz, its a 1950 OK "Mohawk Chief" of 0.299 in. minus its back tank. BOB
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Old Aug 08, 2011, 09:44 PM
Time for me to Fly...
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Thanks, Bob. Say, what is the A.M.E.E.?
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Old Aug 08, 2011, 09:46 PM
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Thanks, Bob. Say, what is the A.M.E.E.?
Its the American Model Engine Encyclopedia, by Tim Dannels
http://www.modelenginecollecting.com/
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Old Aug 08, 2011, 09:51 PM
Time for me to Fly...
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Its the American Model Engine Encyclopedia, by Tim Dannels
http://www.modelenginecollecting.com/
Wow.... Very nice! A guy like me prolly ought to have one of those.

Thanks!
Wiz
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