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Engine basics => Engine set up tips => Topic started by: Robert Zambelli on October 13, 2011, 09:03:37 AM

Title: Stuff your bypass??????????????????????????
Post by: Robert Zambelli on October 13, 2011, 09:03:37 AM

As many of you know, I really like the Fox 35. I have quite a few of them and I'm more than pleased with the way they run.

Aside from different needle valves, extra head shims and gasket elimination, my best running Foxes are COMPLETELY STOCK.

Although I've not tried it, many people stuff the bypass port with epoxy or wooden pieces.

While making a new bushing for a friend's Stunt 35, I noticed that the bypass port was partially filled with a brown material - I assumed epoxy.

Looking closer, I noticed that the material was separating from the crankcase at the lower end. I'm not sure how much of the material was detached but if the separation went high enough, the material could break away.

Logic tells me that the cause is the heat cycling of two material with different coefficients of expansion.

Maybe it would be better to use and aluminum filled epoxy.

Bob Z.

Title: Re: Stuff your bypass??????????????????????????
Post by: Steve Fitton on October 13, 2011, 12:31:40 PM

Is that a shiny new bushing I see in that case?   #^

Title: Re: Stuff your bypass??????????????????????????
Post by: Tim Wescott on October 13, 2011, 12:52:14 PM

It looks like bits already have broken loose.

Title: Re: Stuff your bypass??????????????????????????
Post by: RandySmith on October 13, 2011, 01:11:09 PM

Quote from: Tim Wescott on October 13, 2011, 12:52:14 PM

It looks like bits already have broken loose.

Which is a problem, I have seen many motors that had ruined parts from parts coming loose inside

:-(
Randy

Title: Re: Stuff your bypass??????????????????????????
Post by: Robert Zambelli on October 13, 2011, 01:33:36 PM

Steve asked:  "Is that a shiny new bushing I see in that case?"

Yes, Steve, it's the custom re-bushing I do on older engines with worn out bushings.
The material is manganese bronze which is, in my opinion, the absolute best bushing material.
It's better than silicone aluminum bronze and orders of magnitude better than oilite.

Bob Z.

Title: Re: Stuff your bypass??????????????????????????
Post by: RandySmith on October 14, 2011, 08:31:55 PM

Quote from: Steve Fitton on October 13, 2011, 12:31:40 PM

Is that a shiny new bushing I see in that case?   #^

You can tell that it is a non stock bushing ( read new aftermarket )  because it has a very nice chamfer.radius on the new bushing  :-)

may even be a part of a Fiat or Alfa Romero engine part  :-O

R

Title: Re: Stuff your bypass??????????????????????????
Post by: Jim Kraft on October 20, 2011, 08:37:14 AM

If the epoxy is coming loose like that, it was probably not properly cleaned before adding the plug. I have done several Fox 35's with JB Weld, and never had a problem with it coming loose. I clean the case with lacquer thinner before adding the JB. I have also done the wooden plug thing. Both seem to work.

Title: Re: Stuff your bypass??????????????????????????
Post by: Robert Zambelli on October 20, 2011, 02:45:58 PM

Hi, Jim - I looked closely at the epoxy. It is definitely not JB weld. It's some sort of plain adhesive with no metallic filler.

I agree - JB Weld is the way to go.

     Bob Z.