My OS 46 fxi has no pinch left, but runs well. I remember reading something about it not having as much compression as the fx or ax. Would it be ok to pull the shim out of the head to bump the compression up a bit? I thought it might help out.

Experimentation is the name of the game. Try it. Though it's advisible to get new head bolts. Esecially if you end up putting the shim back in. If you take the shim out and it runs poorly you could also try less nitro after the shim is out.

Why would the head bolts need to be replaced?

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Do not confuse "Pinch"  with compression.     two different things   cylinder pinch or taper is just that its tighter at top dead center and with most sport engines that are set up rather mild the pinch will gradually become less noticible when turning over by hand or completely disappear early on.      That does not mean it has lost compression.</p>

Trying to improve performance by loosing a gasket usually ends in frustration but try it if you want.    There is no reason to replace cylinder bolts if they are not damaged.</p>

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John</p>

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they strech just like any car or motorcycle head bolt. It's not as drastic or as critical but they do strech.

I know the pinch is different from compression. It definitely has no pinch, it has no resistance when turning over by hand and the plug out. It actually has great compression still, but was wondering about the effects of trying this. My theory simply comes from what I heard about this engine not having as much compression as the fx or ax from the factory. I may throw her on a stand and see what happens.

I run a TT PRO 46 without a shim.  It came that way, used, and I didn't find out the shim was missing for quite a while. 

I run it on MasterPower 15% nitro, 18% oil (1/3 castor / 2/3 synthetic).

Sweet running engine.

Jack

So long as the head still seals properly against the liner there's no problem taking out a shim. Most engines have about a .2mm shim which won't change the compression all that much given that they're all a fairly low compression to start with. Pinch is highly over-rated and disappears when the engine is turning over fast enough. That speed is about what you can give it by a reasonable flick (so long as there's an oil film between the piston and liner).

Hi Brett, If your really bothered about the lower compression then just get an FX head. You may be just wasting your money though because I had an fx that had stripped glow plug threads and I was able to buy an fxi head cheap so I just replaced the head. No difference that I could tell in the way it ran. The engine belonged to a flying buddy so I was familiar with it.
 Fred