IM WORKING ON A 2000 400EX for someone else. I want to know if it is standard bore or if it has been bored. Bore size is 3.384 piston size 3.379 Is that standard?

Ring gap is .021 or 53 mm less than .001 taper Bore looks very good with some cross hatching still visible. Is the ring gap too wide? Also the two exhaust valves are slightly bent. Happened when the chain jumped. Replaced the chain but now it burns oil very badly. Also was run low on oil. Exhaust valve guides seem loose. Will replace exhaust valves, guides and seals. Any recommendations on what to do with the bore and cylinder. Cheapest fix. Also where's the best place to get parts? Thanks for the info. Any help would be appreciated.

 

the standerd bore is 85.00mm......if it still is showing cross hatches the bore is in good shape ..unless there are vertical scratches present..if you want to go with a fresh topend....ebay has the chepest piston kits ive foundand probaly everything else you need ....but shipping ...getting valves ,seals,gasket kit,unless you can get them all from one seller and request combined shipping ...you may fair better at rockymtatvmc....or denniskirk...they both offer free shipping for orders over 100.00

 

i did a metric to standerd conversion for you..standard..85.00mm= 3.3456 inches...
...86mm=3.3858inches wich is the 40 overkit sounds like this will work great with a little honing....i found a 40over kit on ebay including the topend gasket kit for 109.99 buy it now ......serch 400ex piston and youll find plenty

 

Did you measure the cylinder out of round..?.. did you measure the valve stems & guides..?

 

havn"t checked bore out of round yet, but the exhaust valve guides are loose,will replace guides and exhaust valves