I have a Fox 40 Stunt (model 14000) that I bought some years ago on Ebay. It seems to be in almost new condition since it has great compression, no scratches on the mounting lugs and a nice shinny, clean finish overall. My question is, "Is this a decent engine for stunt?"  I've heard conflicting reviews and it leaves me puzzled   .  What say ye experts? 

  Tom, is that the one that has a bolt on venturi and the "wart" bypass boost port? It is sometimes called the "large case" engine.  If so, it makes a decent stunt engine out of the box except it is a little on the heavy side.  Lew Woolard does rework those some too though and when he gets through they are pretty darn good.
 

  Bigiron

Tom - I spoke to a Fox sales/marketing guy many years ago about that engine.
He told me that it was designed and/or developed by George Aldrich and intended specifically for stunt.

I would suggest NOT modifying it until you try it. You may find that it's fine as is.

Bob Z.

Think of it as a Fox 35 on steroids, I learned the stunt pattern with that engine on a really big profile back in the 70's. Still have the engine which is now powering a Dancing Girl bipe (same wings as the 38 Special). I wouldn't hesitate to use it on anything around 500-550 sq/in. Only real draw back is the large mounting foot print, you almost need to build an airplane specifically for it.

This is a photo of the profiles my buddy and I built to learn the pattern with, he had a Shark 45 kit. We used the 2nd or 3rd rib out from the root, built straight wings and used the Shark numbers for everything else. We both bought Fox 40's to power them with and I don't remember either one of wishing we had chosen a different engine. Thinking we were running 11-6's either Rev-Up or Top Flight on Super Fuel.

Hi guys,

I had a Fox 40 like this years ago and the biggest problem with this engine I experienced was the very long bronze bushing for the crankshaft got so hot and tight the engine had less power than a Fox 35 or it would seize up. I gave it to someone and they gave it back to me.
Then, a combat guy who ran plain bearing Tigre 35 engines in his planes told me what to do.
First, disassemble and clean engine with alcohol or etc. Use a tiny stone to remove any burrs from any edges on the crank.  Then use progressively finer sandpaper to remove machine marks or rough areas, until the crank looks like it was polished chrome. Lightly polish the bronze bearing with 600-1000 sandpaper to lightly smooth it.
Second, He told me to spin the crank in the empty crankcase and listen. If it makes a zinging sound it is ready to use and if it doesn't then go to the next step. Next you lap the crank in the bushing with old fashion toothpaste. (He used lapping compound but he warned you could easily go too far without experience.) You chuck the crank in a drill and lap for awhile. Stop clean everything up, then spin the dry crank in the crankcase and listen for the zinging sound. If yes -you are done, if not - repeat the process. The goal is a sweet spot that is a low friction fit without any side wobble or excessive fuel blowing out the front. I had a whole new engine that I could finally keep running well enough to properly break-in the piston-sleeve. I changed the mounts to K&B 40 size. This 40 was equal to my Stan Powell K&B 40, using the same prop on the same airplane. I liked it.              Pat Robinson

   

I wouldn't hesitate to dill another set of holes in the engine mounting lugs and/or even cut them down to help make it fit.  This will make some see red but that engines isn't particularly collectable and even if it were once our generation is gone none of this stuff is going to be worth anything. Might as well get as much use out of anything you can now before it's all over.

Hi Ty,
Yep, the getting hot symptoms are what I experienced, except my symptoms were probably worse.
This Fox 40 has the longest plain bearing I have seen in any engine and it adds so much heat to the engine that it distorts the whole break-in process. After I solved the bottom end heat problem, breaking in the piston sleeve became a more normal process, but it does take some time.
Tom,this is a long stroke engine with good torque so I used 12x5 Rev-Up props or cut them down to 11 5/8" x 5 Rev-Up depending on the plane. I also use some 11.5"x 6 props some of the time, in some conditions.
                                                 
                                                                                            Pat Robinson

Glad I decided to look into this thread.  Somebody actually gave me one of these engines a few years ago, and I've been wondering how useful it was.  Really found the reference to one being used on a Shark 45, as I have one NIB, and have been contemplating using my ST-51.  The Fox would be more in keeping with the era.

I agree with Brett, we used them on Shark sized profiles but times have changed and the profiles were much lighter than a Shark can be built.

   I don't think that's going to be a good combination unless you build it very very light. It's nowhere near as powerful as an ST51 (or a 46, for that matter) and that's about as small an engine as I would use.

   Brett

Hi  Brett is 100% correct , and telling you like it is, that is NOT the motor to use for a plane as large as a Shark
It would be a good Chipmunk motor or a plane of that size, try to keep it in the 525 to 585 sq in range
The Shark need a motor that will deliver a lot of power.
Randy

While we're on the topic of Fox .40s for stunt, does anybody have an opinion about using the Fox .40 Schnuerle, both the older large case, and the current small case, and/or the Fox .45/.46 large case Schnuerle?  I have at least one of each, and a couple of the Fox CL venturi assemblies for the large case engines.

Reason I'm asking, is I once had an RC Bipe somebody gave me that was about a pound heavier than the suggested build weight, and the only engine I had that fit it was the small case .40.  Took forever to get off the ground with a 10-6, needed a short dive to build up speed for loops.  Then, I switched to a wood 11-5, and while the RPM dropped to just above 11,000, the takeoff run dropped to about 100', and the plane started flying like it should, inside and outside loops from level flight.  Just kind of suggested to me that the non-carb .40 version would be fairly decent with an 11-5 or 12-4.