Howdy folks,
I've received a Fox motor that I was told was a Fox 35 stunt, but it is slightly bigger physically, has a slanted glow plug, off center and has a 4 bolt backplate as apposed to 3. No size stamped on side, just Fox. No webbing between venturi and cylinder either. The venturi is round not square like the combat 36.

Okay, I've identified it as a Fox 36 Stunt, next question. Are these any good at all?

Is it that engine?
http://www.rojobcn.com/technic/avion/fox36rdfs.htm

Not quite, the venturi on mine is higher and slopes down to the front.

Originally Posted by baldguy

Not quite, the venturi on mine is higher and slopes down to the front.

The engine pictured looks different because it was an RC engine. It was converted to CL with a venturi and needle valve assembly in place of the R/C carb. the stock CL engine has a longer venturi cast the case.Engine was designed for a CL event that never materialized and there is also a 29 counterpart with the displacement stamped on the mounting lug. They are not too bad but have a tendency to vibrate a bit till broken in. They are not a great 42/4 in my opinion but do well when run in a wet 2 cycle. They are much better engines in my opinion than the Fox 35 but as I said that is my opinion only.

Thanks.

Originally Posted by coriolan

Is it that engine?
http://www.rojobcn.com/technic/avion/fox36rdfs.htm

The engine pictured is, I believe, a special variant of which only 50 left the Fox factory in 72. The pictured one uses the Fox 36 x BB /NB head and a larger, bored out venturi. The inners are pieces of early Fox combat engines with a plain bushing.
Performance ? To begin with, it's not a stunt engine. I have one in a Larry Scarinzi Killer and it is a very powerful engine with a loud , ear piercing exhaust bark. Meant for speed.
To clarify what the original post asked, that motor with the four bolt backplate is either a Fox 29 ( not on crankcase) or a Fox 36 standard. At first, Duke Fox produced them for slow combat where the rules at that time specified a plain bushing engine. The head is taller and fined and the venturi is narrow and tall. Duke later made R/C versions which were also popular with the Navy Carrier u-control guys who used them in profile carrier. That event back then also required a plain bushed engine.

The 1972 Fox 29 does indeed look very similar!
http://www.rojobcn.com/technic/avion/fox29cl.htm

Originally Posted by f.imbriaco

The engine pictured is, I believe, a special variant of which only 50 left the Fox factory in 72. The pictured one uses the Fox 36 x BB /NB head and a larger, bored out venturi. The inners are pieces of early Fox combat engines with a plain bushing.

Actually, all of the early production runs of the Sport 36 came with the exact same 36X cylinder, piston, wrist pin, and connecting rod. The shaft was shorter than the one in a 36X.

Performance ? To begin with, it's not a stunt engine. I have one in a Larry Scarinzi Killer and it is a very powerful engine with a loud , ear piercing exhaust bark. Meant for speed.
To clarify what the original post asked, that motor with the four bolt backplate is either a Fox 29 ( not on crankcase) or a Fox 36 standard. At first, Duke Fox produced them for slow combat where the rules at that time specified a plain bushing engine. The head is taller and fined and the venturi is narrow and tall. Duke later made R/C versions which were also popular with the Navy Carrier u-control guys who used them in profile carrier. That event back then also required a plain bushed engine.

Only an assortment of local-only rules ever specified plain bushing shaft engines for Slow Combat. The AMA Rules didn't cover a Slow Combat event until after the 36X was replaced by the Sport 36.

Duke was taking a chance to change models before the rules were added to the rule book, and was pretty annoyed with some people who kept assuring him that the engine restriction was going to be in the rules.

I can't verify the number of special versions that there may have been, with the tall venturi cut shorter and bored out like the one pictured; I only saw one or two back when they were current. Every one of those types that I ever saw running up close vibrated like mad. I think they were equally bad as the Series 1 and Series 2 Combat Special of 1955 and 1957 had been.


Kiwi

Can't be a .29, it's physically bigger than my .35's, so it must be the .36. Gonna have to send this one back to the seller, I need a stunt motor.

Frank Imbriaco is correct. I built that batch of 50 engines for Fox in 1972. The engines were to be passed out at a major contest in an attempt to get Fox engines established and hopefully a win in the supplemental Slow Combat event that was being started at the time.

I had one and shook so bad no matter what was done. Once up to RPM was much better. Made .35 Stunt look like smooth runner.

Originally Posted by LA Ming

Frank Imbriaco is correct. I built that batch of 50 engines for Fox in 1972. The engines were to be passed out at a major contest in an attempt to get Fox engines established and hopefully a win in the supplemental Slow Combat event that was being started at the time.

Hi Andre: Thanks for your input. Well, I guess there isn't anyone who can retort being as you are the person who hand assembled the 50 engines that I spoke of.
As you know, mine isn't a shaker. Runs as smooth as any Fox combat engine because the needle is peaked to run at a high rpm.
If one attempts to run it to the rich side for a stunt like run, its going to shake because of the design- porting, timing, compression, etc.- the works.
Hope this clarifies for the original poster. Keep the engine- mount it in a an aircraft with the intention of good high speed performance.

Dankar:

Are you referring to a "stock" out-of-the-box Fox 36 Sport? Or, did you also have (still have) one of the 50 engines that I built while with Fox Mfg? Frankly, I don't recall ever testing how those prototypes ran at less than full-scream. Full scream and good needle setting consistency while maneuvering was the goal.

IF you had one of the hand-built engines I built while at Fox Mfg, you had/have a very rare factory modified Fox engine that ought to be documented/saved, and if you have no interest in it, passed on to someone that does have an interest in preserving Fox Mfg history.

Frank:

There are three external spotting features that make my hand built/modified Fox 36 Sport engines identifiable:

* The polished 36X head. (And those were of the ring-relief variety,)

* There is a very slight mismatch between the larger diameter of the case fins and the smaller diameter of the 36X head. This is important because there was one very small batch of Fox 36 Sport production engines that were released that also used the same 36X head. That's a long story. So here's the short version: The original head design for the Fox 36 Sport was too light and the head distorted when the head screws were tightened. Fitting a 36X head to them allowed me to keep engines flowing out the door as we waited for the re-designed heads. I had the fins on the case of the production 36 Sport's slightly kissed while mounted in a lathe fixture so as to have them match the slightly smaller diameter of 36X head. Yes, that was a small visual eyesore, but to me it helped the production engines look more "finished".

* The opened and re-shaped venturi. The venturi was bored to the maximum that still allowed acceptable fuel draw (running it on pressure is even better, but not allowed by the rules for the event it was built for). The squaring of the stock angle cut venturi was an identification feature. I would have preferred to use the longer stack the stock Fox 36 Sport has, but a quick identification for the modified cases was needed so they would not be mistaken for a stock 36 Sport among the thousands of engines at Fox Mfg during that time.

My, that was so long ago.

Edited to add I.D. point #2 I happened to think of.

[QUOTE= The AMA Rules didn't cover a Slow Combat event until after the 36X was replaced by the Sport 36.




Kiwi[/QUOTE]

I flew OPEN fast combat at the 1972 Glenview , IL N.A.S. NATS. As I recall, it was an old day marathon. Nearly 100 entries. But on a
separate day, slow combat was flown with plain bearing engines( Fox, ST, etc. )with a .36 displacement limit. It wasn't a sanctioned NATS event , though- but it happened and awards were given.

As far as my previous comment about profile carrier and my use of a plain bearing Fox 36 x R/C engine( large case ala the BB & NB versions) at the very same NATS- somewhere I have a photo of Duke holding my profile design. He hung around a good part of the day at the Profile Carrier event ; not only because he was interested in the outcome, but because he was adapting product to the rapid pace of new events.
Soon afterwards, he marketed the Fox 36 Sport in an R/C version and dropped the Fox36x (large case) plain bearing engine.
I plan to discuss this with Scarinzi tomorrow at the GSCB Collecto. He has amazing recall .