My head has only one shim, but i run 96 octane fuel. 100 octane and 91 1/2 and 1/2, I run klotz R50 oil. and a 18X6 at just over 8000, i pulled the engine last night, the bearing is a HK0808 8X12X8 mm. PE do you know the exact nominal size of the crankpin? I used to work in small engines, snowmobiles and ect, we rebuilt cranks at our shop and most of the time the crankpins were ok with a slightly bad lower rod. so hopefully mine is within tolerance. It seems like the rod is rubbing on he backplate more than it should. It has worn a probably .010" grove into the back of it. when i pulled the backplate i noticed some small metal shavings on the end of the crankpin, i am wondering if these are entering the bearing and causing it to prematurely fail. The other times the engine has failed it has been under warranty, now that it is not underwarranty i want to catch this thing before so i dont have to do a complete rebuild after the bearing particles ruin the piston and sleeve and take out the crank.