Can I bore my stock 1340 cylinders to .040 over. Keith Black sells some .040 9.5:1 compression pistons for this engine. That is the highest they sell. I figured since they sell them that high, then it must be acceptable to bore to 040 over. Is this OK? What could happen? The .020 KB pistons that were orginally in the cylinders have some "slop" when I put them in the cylinders without the rings. I am afraid that a .030 overbore won't take out enough wall to even out for the new set of KB pistons.

 

Anyone bored 040 over without problems? I am ordering my pistons today.

 

My 83 fxrs I think was bored 040 over. The piston I have says 040 stamped on them and the inside is stamped H-D jcc 292. But I'm not sure if that was bored over or is it a cast number. Anyone know if it was bored over or is it a cast number?

 

just remember, the thinner the cylinder material, the hotter it runs. you do not want to bore it any more than necessary.

 

The MoCo sells oversized pistons up yo .030" over. Is it OK to go to .040" on stock cylinders? I suggest you contact KB for their advice.