hi,
currently i'm trying to re-shim the head clearance from 25% to 16% nitro, however i've noticed something 'weird'...

the sleeve is sitting below the engine casing, maybe about 0.3mm below. is it possible and normal?

initially the head shims were 0.4mm, now when i tried to use 0.3mm, the buttonhead doesn't really fit totally into the sleeve as it is prevented from fitting totally into the sleeve by the engine case!

something wrong? seems to me that the minimum head shims got to be 0.4mm or more...

p.s. engine concerned is the nosram rs12speed (aka lrp spec3?).

I'm not familiar with your specific engine, but tell me if I understand what you said.

With the sleeve inserted into the block... If you laid a straight edge across the top of the block (where the head would go) the straight edge would not touch the sleeve. There would be a gap?

Do not shim under the sleeve. That would change port timing. Just live with the original shims.

it's the buttonhead shims that i'm talking about; not shims under the sleeve.

what he trying to say is when sleeve is insert into the crankcase, the top of the sleeve is not flush with the top of the case instead it sit into the crank. Therefore instead of the button head resting on the sleeve it is reasting on the crankcase, which might cause an air leak!

Nitro, that's totally wierd. every engine I've seen is designed to pinch the sleeve between the head button and the block.

I would pull the engine completely apart and measure stuff...

Rod length (center to center)
exhaust port (from top of sleeve to top of port)
transfer & boost ports (measure same as exht port)
TDC (top of sleeve to pistion face; bolt down the head and turn the crank to TDC, pull the head and measure)
BDC (after TDC measurement turn the crank to BDC and measure from top of sleeve to pistion face.)

These measurements will tell me you port timing. Then we will know if you can get away with shimming the sleeve to correct the problem.

Shimming the sleeve will not correct the problem since you would then have to remove the same amount of head shims to get the proper head clearance and the head would still hit the crankcase.

This is an unusual problem. There are motors where the sleeve is slightly recessed in the case but they usually have a shoulder on the head to raise it up out of the way. Is this motor all stock with all original components?

I was saying dont try to correct it with shims under the sleeve.

can you post some pictures so that we can help you easier??