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Fox .15 piston liner

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Fox .15 piston liner

Post  oldguy on Thu Jul 19, 2018 4:33 pm

This question is to Ken and anyone who can give info on this topic.  This came to my attention on another post which Ken commented on, that the piston liners on some of the older fox .15's, that there was   a shim under the head of the liner that could be removed. So I went to checking for this on my fox .15 engines and didn't find any. Well I got to looking again because I noticed that on some of the engine the head sits up higher about .020 higher it's quess.  After inspection I see where the difference is, it's the liner that is the difference, some of the liners have a thicker portion at the top. There is no shim, there just thicker a the top rim.   My question here is I want to shave down the tops of the liners to gain more compression.  Anyone see why this would be a problem. There is plenty of room between piston and the head to do this. Comments. You can see this difference from these two pictures.



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Re: Fox .15 piston liner

Post  Ken Cook on Thu Jul 19, 2018 5:16 pm

Is the shim under the liner? I can't recall where it was on top or underneath I just know I have them in a bag. Now to answer your question, I sand down all of my Fox liners, because Fox made them and they're not typically flat. So sanding down the liner is a very acceptable practice. I do it with the backplate as well. Especially on the Fox .35. I sand the back of the case and liner on a piece of glass and then I take a piece of sandpaper glued grit out to the back of the case. I then lap the backplate. The stock cork gasket works but it has a short lived life usually becoming squished out. This gives the mating surfaces of both parts a little more to sit on. Just make certain that  the baffle doesn't hit the head. Check it with no plug in the engine.

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Re: Fox .15 piston liner

Post  oldguy on Thu Jul 19, 2018 5:32 pm

Ken Cook wrote:           Is the shim under the liner? I can't recall where it was on top or underneath I just know I have them in a bag. Now to answer your question, I sand down all of my Fox liners, because Fox made them and they're not typically flat. So sanding down the liner is a very acceptable practice. I do it with the backplate as well. Especially on the Fox .35. I sand the case and liner on a piece of glass and then I take a piece of sandpaper glued grit out to the back of the case. I then lap the backplate. The stock cork gasket works but it has a short lived life usually becoming squished out. This gives the mating surfaces of both parts a little more to sit on. Just make certain that  the baffle doesn't hit the head. Check it with no plug in the engine.

Well thanks Ken. I will just go ahead and see what I can do about sanding off .020 off the top of one of the liners and see how it goes. At the moment I have 6 of these slant plug .15's. And I found no shims in any of them. What I did find is that 3 of them have liners in them that are close to .020 thicker at the top of the liner.
thanks

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