what piston do I need?

[rubbersdown]

bought a 400ex from a guy as a project. didnt come with a piston and the guy said it had a 440 sleeve in the cylinder. the bore measures 88.88mm does that sound right for the "89mm" piston or is that the bore for the 88mm piston? trying to figure out what piston I need!

[F-16Guy]

If I remeber correctly, most "440" kits are actually 434cc with 88.5mm pistons. I don't know what the clearance is supposed to be, but it might be for that. They do make oversized pistons for an 88.5mm bore, so check out Wiseco or JE and see what they have - you may also want to look at Namura. It might be a good idea to go oversize just to freshen it up and get the right piston to cylinder clearance. If you're going to put together a 440, you should read this:

http://www.exriders.com/vbb/showthread.php?s=&threadid=8316&highlight=decked+cylinder

Also, I'd bet this engine is apart because it keeps blowing head gaskets. If it has stock head studs, you'll need to either send the cylinder to GT Thunder to have their HD studs installed or have a local machinist repair the holes with threaded inserts and reinstall the stock studs. It may look okay and the head may even torque down okay, but once it gets warm, the stock studs (usually the forward one by the exhaust port) will loosen and cause another blown head gasket. Fix the studs, get the right piston, and slap it back together - and don't forget to throw a stage 2 HotCams cam in it!!

[rubbersdown]

yah im going to take it to my machine shop guy tomorrow and have him measure it for me then ill just call wiseco and tell them the measurement and have them tell me what piston