400ex no compression after rebuild

[Warrioreater400ex]

Hello, me and my friend rebuilt our 2nd 400ex the other day, we followed the book and throught e did everything right, however when we try to start it, it sounds like it has no compression, the starter turns fast and it just doesnt sound like its hitting, we have spark and fuel. We have the timing on top dead center, the T on the flywheel with all the cam lobes straight down.

Im thinking it has to be in the head/valves. I wire brushed the valve faces to get the carbon off, but i didnt even touch the valve seats with the brush. Maybe the valves need to be adjusted? any i deas? it must be something big because we have NO compression. i can spin the flywheel with one hand pretty fast without feeling any compresson.

[sixer3]

sounds like a valve train/ timing problem, re-adjust your valves and also make sure that when the t-mark on the flywheel is lined up that the marks on the cam chain sporcket are parallel with the head...in my 400 the lobes arent completely facing straight down but real close, sounds like your cam gear may be off a tooth or 2 and not all the valves are closing at the same time...good luck

[1fst400]

did you adjust your vavle clearences? if not then it could be just holding one valve open all the time.


if thats good. then you can buy a valve seat grinder. they are cheep. they are a little suction cup that goes on the valve.

you take the spring off the valve, put some of the grinding compound on the seat of the valve and the valve. Then spin the valve useing the suction cup. its real easy.

[abuckley1290]

if it is the stock cam did u put back in the small spring and plunger for the stock decompression? If u didnt that will cause it to have no compression