400ex rebuild

[jason_david1]

i have a 400ex that is blowing smoke. im not sure if its the valve seats or the rings. i have never been in a 400ex but i have rebuilt several 450r's and yfz's. is there anything else i need to look for when doing it? should i just rering or get a new piston? can i reuse the cylinder if in spec? are they steel sleeved or nikasiled (sp)? any help would be greatly appreciated.

[levonskinator]

I recently rebuilt my 400ex. I bought it and it was smoking pretty bad. I was able to use the stock piston over again, I just honed the cylinder and replaced the rings. I would defiantly replace the valve seals. They are pretty cheap and while you have the head off you might as well, assuming you have access to a valve spring compressor.