Fox 35 Stuffer Backplate Question

I have a Fox 35 on which I decided to try a stuffer backplate. I took off the old backplate, which had a new gasket (been on there two days) under it and ised that gasket with the new stuffer backplate. this is an older Fox engine, probably vintage late 70's. After tigtening everything up, I found that the enegine was very stiff: the bottom of the con rod was in constant contact with the back plate.

I took this off, put the old backplate back on and all was well. So, I decided to try it on a new 50th Ann. Fox 35. This time, I used a brand new gasket on it becasue the old gasket distintegrated (naturally). After tightening everything up, it was fine and there was no stiffness.

I'm naive and always thought a Fox 35 was a Fox 35 was a Fox 35, but now I wonder if there's a difference of a few thousanths of an inch in the rear of the casting.

Does anyone know?

Kim Elmore
AMA 56239

All Fox 35s resemble each other. The resemblance ends when you pick up a set of calipers.
Pat MacKenzie

The rod on your 1970's Fox .35 is running halfway off of the crank pin. It is probably starting to get badly worn. The problem is probably either a bent crankpin or a bent rod.

LAST EDITED ON Oct-14-04 AT 09:12 PM (CDT)
 
Basically what Pat says is true. The manufacturing tolerances vary quite a lot throughout Fox 35 stunt engines. I found that the end of the crank pin to the face of the stock backplate varied between 0.040 inch to 0.070 inch when I was making the backplates. I still have the original instructions for them and they may hekp you. I need your E-mail address so I can scan the diagrams and instructions to you.

Bigiron aka Marvin Denny

Kim, I tried to send the Stuff through the e-mail above, but it won't go. E-Mail me at [email protected]

>I have a Fox 35 on which I decided to try a stuffer
>backplate. I took off the old backplate, which had a new
>gasket (been on there two days) under it and ised that
>gasket with the new stuffer backplate. this is an older Fox
>engine, probably vintage late 70's. After tigtening
>everything up, I found that the enegine was very stiff: the
>bottom of the con rod was in constant contact with the back
>plate.
>
>I took this off, put the old backplate back on and all was
>well. So, I decided to try it on a new 50th Ann. Fox 35.
>This time, I used a brand new gasket on it becasue the old
>gasket distintegrated (naturally). After tightening
>everything up, it was fine and there was no stiffness.
>
>I'm naive and always thought a Fox 35 was a Fox 35 was a Fox
>35, but now I wonder if there's a difference of a few
>thousanths of an inch in the rear of the casting.
>
>Does anyone know?
>
>Kim Elmore
>AMA 56239

Paul Smith

I lived in Wichita from 1973 to 1977. As true deciple of Marvin, i stuffed everything I could get my hands on. Fox, Supertigre, OS, etc.

Having the crankpin hit the backplate is just another day in the shop, Grind the crankpin and the bottom of the rod 'til it just clears. That way, you are maximum-packed. Now that I'm out of combat I can revel these secrets.