Originally Posted by
ugglasdav
Thanks HHH for the reply, for some reason i dont thing the pitting will come out of the piston, the pitting is really bad and the pits them selfs look quite deep into the piston, im running 0.30 mm head shims witch is the standard for the Torque, i am also using 25% fuel
Feel the bearings with your finger. If they are smooth, then I would recommend a new piston/sleeve/rod/button. Make sure you have at least .50mm of head shims. That makes a head clearance of .50mm. I run .55mm of shims in my picco based engines. .12, and .21 engines.
The picco .21 engines including the idm come with .40mm of shims. That's too low for 25% nitro. It's too low for 20%. The stock clearance is ok for 16%.