RE: Picco .90 Marine Repair?
To:wires37..........question about sleeve shims.........
It can be true,but...... it also can be false..........There is no one size fits all answer to your question.
A shim added under the sleeve can either help[sm=thumbs_up.gif] or hurt[sm=thumbs_down.gif] your motors performance and reliability.
Without knowing what the timing numbers[intake,exhaust and rotor] you presently have incorporated in your Picco .90[there were several versions],the fuel you are running,your motors combustion chamber design and volume,the type and weight of your boat and the pipe you are using,I hesitate to recommend any changes in sleeve height.
A blind recommendation to a sleeve shim size is just asking for potential motor trouble.Un-informed arbitrary motor modification recommendations can result in a trail of destroyed engine parts.[sm=disappointed.gif]
You probably already know this but for others that might read this thread............The biggest enemy of larger displacement nitro motors
[.45's on up] is the lean run.............Adjust the needle valve to just get the motor out of its 4 stroke operation and into a "rich side" 2 stroke operation and then leave the needle alone.Do not "squeeze" the needle.If at W.O.T. your motor is "sagging",you are killing the piston & sleeve and sometimes the conrod bushing.
I hope this helps[sm=wink_smile.gif]......Rod Geraghty