Caculations worked out to be 68-70 percent close will be ok. It is rm500 piston. Have found 2 one 90 mm one 90.5 which is last bore. Explains .060 on piston factory bore 88.5 on rm 500. Also most pics of rm500 cylinders I have found do not have exhaust bridge.

Here's port map. After very close inspection liner at boost prt cracked. Gonna send out to LA sleeve next month to be resleeved. Guess gonna eat larger bore pistons just to have on hand don't make anymore. Got factory bore nos wiseco for 40 bucks. Gonna try to get all 4 bore pistons that way can keep Engine going for long time.

That sucks.

Line the piston you have up with your port map. Place the piston at the bottom of blowdown - just at the point where the transfers are open.

Now look at where the piston lines up at the boost port. Is the piston close to those little bridges or? I'm thinking the piston rocked slightly inward a bit and overheated on the intake side. Does the piston show wear at the skirt bottom intake side? Were the piston edges chamfered?


Is it possible to find cast piston for RM500 from ProX/Art/Wossener? What does CW Racing sell? Wiseco forged pistons need more clearance. I'm thinking if you can use a cast piston with tighter clearance this type of issue won't happen.

Or I guess you could have LA Sleeve leave a few more mm of bridge material.

just bumping this ahead of the spam