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Author Topic: Fox 35 Repair  (Read 1796 times)

Offline Al Cantrell

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Fox 35 Repair
« on: November 14, 2022, 08:43:38 AM »
Hello,
I'm still working to get my old ringmaster and fox 35 ready to fly.  This weekend, I cleaned up the engine and made some discoveries:

1. Discovery one - the prop shaft is stripped.  It tightens up to a point where it is almost tight enough and then gives way.

2. Discovery two - the needle valve keeper.  If that's the right word, only has one ear on it.  So what normally looks like a letter U with long legs only has one leg.

Would you please give suggests for repair? 

Thanks,

Al

Offline john e. holliday

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Re: Fox 35 Repair
« Reply #1 on: November 14, 2022, 10:43:35 AM »
Is the shaft long enough to put washers between the nut and prop so you still have theads for tightening?  As far as the needle valve ratchet cut a peice of tubbing to slip over the needle.  That will help seal the needle.  The one side should be enought to keep the needle from moving. D>K
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Offline Al Cantrell

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Re: Fox 35 Repair
« Reply #2 on: November 14, 2022, 11:02:41 AM »
Thanks, Doc! I believe it is long enough.  I will give it a try. It will be a nice simple solution.

Offline Dan McEntee

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Re: Fox 35 Repair
« Reply #3 on: November 14, 2022, 12:23:20 PM »
Hello,
I'm still working to get my old ringmaster and fox 35 ready to fly.  This weekend, I cleaned up the engine and made some discoveries:

1. Discovery one - the prop shaft is stripped.  It tightens up to a point where it is almost tight enough and then gives way.

2. Discovery two - the needle valve keeper.  If that's the right word, only has one ear on it.  So what normally looks like a letter U with long legs only has one leg.

Would you please give suggests for repair? 

Thanks,

Al

    Doc is on the money, but I have t ask is it a stock Fox needle valve? On a stock Fox needle the knurled wheels for the ratchet and the end where you grab it are the same size basically, and has a solid steel shaft in between.  I don't think I have ever seen a stock Fox unit with just one ratchet tang on it unless one has broken off.. Some US unit have also. If the shaft threads are stripped, Doc has the solution. Are you sure it isn't just the nut? I would replace the nut also.. It is a fine thread 1/4"-28 nit found a lot of places or swap it out with another engine. When seating the prop, the prop drive plate has four small notches in it that need to be aligned up with the matching bosses on the crank shaft. The drive washer may just be catching on the boss and slipping off when torqued. Make sure everything is where it is supposed to be. I have just never seen a Fox crank shaft with stripped threads at that point. The shaft threads are pretty hard and will strip a nut first,  usually. You will have to experiment with the fuel line length but I cut a piece just a little longer than the distance from the side of te venturi to the ratchet wheel on the needle. Just enough longer so you get some compression of the fuel line. This needs to be done anyway to seal the spray bar threads like Doc mentioned. Greatly improves the run of the engine.

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Offline Al Cantrell

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Re: Fox 35 Repair
« Reply #4 on: November 14, 2022, 02:21:54 PM »
Hi Dan,

I purchased the Fox 35 from a friend in the early 80's on Goldberg shoestring stunter and it had low hours.  I don't think the needle valve had been modified as we were just older teens at the time and didn't know about engine mods.  I think the tang has just broken off over the years.

Thanks for the extra things to check.  Maybe it is the nut after all.

Al

Online Brett Buck

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Re: Fox 35 Repair
« Reply #5 on: November 14, 2022, 05:21:51 PM »
I would have to agree with Dan, stripped threads on the crankshaft would be a very unusual failure.
 
          Brett

Offline Dan McEntee

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Re: Fox 35 Repair
« Reply #6 on: November 20, 2022, 09:49:47 AM »
  I re-read this thread and another thing came to mind, is the nut threading onto the shaft fully? In taking apart Fox .35s of different vintages all through it's production life, the length of the shaft can vary. Some of the older versions had a shaft end that was shorter, and then you have previous owners that may have decided that he needed to shorten the shaft for whatever reason. Either way I have seen some that are shorter from the factory because you can still see the way the end of the shaft is machined.
  I'm curious as to what you found out.
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    Dan McEntee
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Offline Steve Helmick

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Re: Fox 35 Repair
« Reply #7 on: December 11, 2022, 11:19:51 PM »
The shaft/nut problem might be fixed already, but I would note that the earliest Fox .29/.35 used an out-sourced NV/Spraybar assembly..."Austin Craft" seems correct to me, and my recaller says the clicker spring on those was a one-side-only deal. So, I'm wondering if it's one of those. Even in a later engine, maybe it got replaced at some point from one in stock at the LHS? Also seems like maybe "Perfect" had a universal NV/Spraybar assembly? ??? Steve
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Offline Colin McRae

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Re: Fox 35 Repair
« Reply #8 on: December 16, 2022, 03:42:19 PM »
MECOA still sells a NVA for the Fox 35. I have a used a few of them and they work great. Also use them on a few McCoy 35's and they work fine.


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