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Author Topic: FOX .29 Stunt Wrist Pin or Good Part Number For One.  (Read 237 times)

Online Dan McEntee

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FOX .29 Stunt Wrist Pin or Good Part Number For One.
« on: January 17, 2022, 10:02:29 AM »
   Like the title says, I am looking for a wrist pin for a Fox .29 Stunt, the one that looks like the .35 stunt. The one I have looked at is hollow, and has brass eyelets in the ends, because there is no wrist pin retainers used on this engine. There is another Fox .29 that came later with square back plate and was a larger case. I don't know if that wrist pin will work for my situation, but if you have one, let me know the dimensions and it may work.
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    Dan McEntee
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Offline Steve_Pollock

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Re: FOX .29 Stunt Wrist Pin or Good Part Number For One.
« Reply #1 on: January 17, 2022, 05:32:20 PM »
Dan, I have bad news.  The wrist pin number for Fox 29 stunt engines, early Fox 25s, the Fox 29X and 29R is (ta-DA!) 5.  Yup, that's "5" as listed on the attached early Fox parts list.  There is no way to do an internet search for anything with a part number of 5 -- I love Fox 29s (my first "big" engine) and I've tried.  The first Fox 25s used a shortened 29 sleeve and piston, but the part number is the same.  Someone might have one, but it would be easier to get a 35 wrispin and shorten it.  You might check with FF and speed people (29X and 29R) but I've found originals to be made of unobtanium.  Good luck!

Online Dan McEntee

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Re: FOX .29 Stunt Wrist Pin or Good Part Number For One.
« Reply #2 on: January 17, 2022, 06:43:54 PM »
Dan, I have bad news.  The wrist pin number for Fox 29 stunt engines, early Fox 25s, the Fox 29X and 29R is (ta-DA!) 5.  Yup, that's "5" as listed on the attached early Fox parts list.  There is no way to do an internet search for anything with a part number of 5 -- I love Fox 29s (my first "big" engine) and I've tried.  The first Fox 25s used a shortened 29 sleeve and piston, but the part number is the same.  Someone might have one, but it would be easier to get a 35 wrispin and shorten it.  You might check with FF and speed people (29X and 29R) but I've found originals to be made of unobtanium.  Good luck!

   Thanks for the information Steve. It's pretty interesting. I have been inside some .19s and .25s and what sticks out in my mind is that I remember having to deal with the tapered wrist pin in one or both of those. I'll have to get that box of stuff out and go through it again.

    If you saw the thread I had on the Tony Cincotta plasma piston and liner sets for the Fox.35 Stunt, it came without a wrist pin and rod. The rod was easy thing to come up with, the wrist pin is the hard part. The piston has no grooves for retaining clips, so there are two options: #1 is to cut down a .35 wrist pin,  round off the ends and just polish up the ends of the pin and let it float, and maybe knurl up one end a bit to help hold it in place. The plasma lining is supposed to be like diamonds and should handle the pin making contact with it while running. Option #2 is to cut down a wrist pin, and pit in some sort of Teflon pads on each end. Option #2 is what I attempted, and what makes that tricky is the bosses on each side for the pin are very narrow, not much meat at all, and making the pin long enough to stay centered but short enough to allow the pads is unchartered territory. I got it done and installed, but the pads are quite thin, and I intend to bench run it a bit and check how it looks, but I want to have something else waiting in the wings if I don't like what I see. I took one of my .29s apart to measure when I was trying to figure out just what I had with this set. The displacement for the set is undersize at .31 so they could make the cylinder liner thicker, as it was made out of aluminum. The piston diameter is something in between the .35 and .29. The .29 wrist pin looked to be a perfect length, and it has brass eyelets on each end also. in thinking about it, this may be a better solution and I may just change it out if I can find one. I only have a few .29 stunt engines and don't want to tear one apart just to rob the wrist pin. I don't intend to use the engine in anything more than a OTS model or a smallish classic model or profile model, and won't get abused, but I want it  to be reliable and trouble free also. I'll have to get back into the .19/.25 stuff and see what I have and how it measures up. I'm afraid it may not be long enough. Thanks for the input !!
    Type at you later,
    Dan McEntee
AMA 28784
EAA  1038824
AMA 480405 (American Motorcyclist Association)

Offline Steve Lotz

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Re: FOX .29 Stunt Wrist Pin or Good Part Number For One.
« Reply #3 on: January 18, 2022, 05:06:02 AM »
The only tapered wrist pin I know of was used in the 15's.


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