400ex engine rebuild

[ny300exrider]

hey guys, my dads 01 400ex is proabably going to need a rebuild pretty soon, its showing some signs of blue smoke on revs after riding for a few minutes. I have never done a rebuild on anything and im wondering what a basic rebuild would consist of. The quad hasnt been ridden too hard but is it a necisity to get a new piston? id rather not bore it because i want to keep it reliable, it that necesarry as well? also can you just get rings and maybe valve seals without getting a bore/piston.

sorry for all of the dumb questions but when it comes to motors im pretty inexperienced.

btw i wont be doing the motor work i just want to know what i should start looking at, thanks

[ckasper18]

Blue smoke is usally a good sign of wear and probably needs a bore .Boring your cyclinder wont hurt reliability as long as you stay with a .010 over bore and dont go with a high compression piston replace the valve seals as well and your bike will be like new and reliable.Good luck

[cummingetit]

11:1 piston will not compromise reliability at all. Throw a cam in at the same time.

[kilabeez0]

how much over is a 416?

[hoser 400ex]

how much over is a 416?

.080 over :D

[ny300exrider]

i defintly dont want a 416, 406 would be the highest. dont want cam or anything either, just something cheap and reliable. its my dads quad and he doesnt need anything faster. so we should do piston/rings,bore cylinder,and valve seals? without labor whats an estimate cost to get the parts for a basic rebuild

[T.Hopp]

I'm in the process of doing the same thing.
Piston, rings, c-clips, wrist pin, gaskets and seals are $173 at one place I searched but I am going to call C&D Racing on monday. I believe they are going to be cheaper with good service also.

[Aceman]

Originally posted by ny300exrider
i defintly dont want a 416, 406 would be the highest. dont want cam or anything either, just something cheap and reliable. its my dads quad and he doesnt need anything faster. so we should do piston/rings,bore cylinder,and valve seals? without labor whats an estimate cost to get the parts for a basic rebuild

If I was you I would take the piston and jug off, take them to a machinist and check the specs. Most likely will need a .020 overbore. Buy a Wiseco 11-1 piston or factory oversize piston take it to your machinist and have him bore the cylinder after looking at the new piston. With the head off pour some solvent, brake or carb cleaner down the intake/exhaust ports and make sure your valves aren't leaking by the seats. If they are lap them or take them to the machinist and have him fix it. Replace the valve seals also.

[ny300exrider]

Originally posted by T.Hopp
I'm in the process of doing the same thing.
Piston, rings, c-clips, wrist pin, gaskets and seals are $173 at one place I searched but I am going to call C&D Racing on monday. I believe they are going to be cheaper with good service also. hey, thanks alot. thats very helpful i had no idea what price range to start looking at.


Originally posted by Aceman
If I was you I would take the piston and jug off, take them to a machinist and check the specs. Most likely will need a .020 overbore. Buy a Wiseco 11-1 piston or factory oversize piston take it to your machinist and have him bore the cylinder after looking at the new piston. With the head off pour some solvent, brake or carb cleaner down the intake/exhaust ports and make sure your valves aren't leaking by the seats. If they are lap them or take them to the machinist and have him fix it. Replace the valve seals also. i would do that but i know i would mess something up, ill find someone local that can do the work and let him see what i needs. if i need to bore the cylinder i will probably go as low as a bore possible and i dont want to up the compression either. thanks for all of the replies