xr400 gasket in 400ex

[greg_gorrell]

i was reading something about using a xr400 gasket to get a better compression ratio on the 400ex. can anyone tell me more about this...im thinking about getting an 11:1 piston now that my rings are going. what else on the xr400 engine is usable on the 400ex besides the cam, how similar are these engines?

[2004exrider]

the xr gaskets are thinner than the ex's. the cam is a little bit bigger than the stock ex's also, and i think it may have a little bit more stroke?

[greg_gorrell]

so you will get a true or really close to 11:1 compression ratio using the thinner gasket than the regular 400ex gasket?

[Speedy81304]

wiseco based there numbers on the 400ex comps with the XR400 gasket, this is what i was told by a wiseco tech. when i was searching for the right piston for my setup.

[nosliw]

Originally posted by 2004exrider
the xr gaskets are thinner than the ex's. the cam is a little bit bigger than the stock ex's also, and i think it may have a little bit more stroke?

nope same stroke

[greg_gorrell]

how would it be the same stroke, i mean there might not be that much of a different, but there must be a change....nosliw, you wanna explain this a little for me?

[yamablaster24]

same crank and rod....:rolleyes:

[smokinwrench]

What about other parts??

CDI for example, I think the xr400 raps to about 12,500 rpm. That would be a mutch better cdi if the electrical conectors are the same.

[nosliw]

Originally posted by greg_gorrell
how would it be the same stroke, i mean there might not be that much of a different, but there must be a change....nosliw, you wanna explain this a little for me?


i don't know how you want me to explain it, but i'll give it a try

400ex - 85MM X 70MM (BXS)
xr400 - 85MM X 70MM (BXS)

[Speedy81304]

the major differents is the transmission, the gear ratios are changed and the gears them selfs are thicker for the added wt of the ATV. the 400ex engine is tuned for grunt and midrange, the xr400 is lighter so it is tuned for more mid - highrange.

the xr400 cdi will not work.
the cam profiles of the xr and ex are a little diffrent with the intake and exhaust lobe sepuration.

[greg_gorrell]

yeah but if you are lowering the head, like you are with the thinner xr 400 gasket, then you are increasing the stroke right?

[nosliw]

Originally posted by greg_gorrell
yeah but if you are lowering the head, like you are with the thinner xr 400 gasket, then you are increasing the stroke right?

what? of course not. stroke is how far up and down the piston moves in the cylinder. depends soley on the crankshaft. thinner gaskets equal high compression ratios. :rolleyes:

[greg_gorrell]

alright...yeah idk what i was thinking...lol

thanks for clearing it up tho

[400exredrider]

by useing a thinner gasket you add to the compression in the top of the cylinder. the stroke is not changed. i use XR gaskets and they seem to work well for me, you could also try Flexsteel Cometic gaskets.

[cam400ex]

i've even heard that you can swap the cases and make it a kick start or making the xr an electric start but i havn't seen one yet completed

[greg_gorrell]

i would like to check into that...a kickstart 400ex would be nice but i would also keep the electric start

[Dannys440]

All over and in the motor and case are the old place for things off of the XR, there is a place for a decompressinon lever on the side of the head,there is the place for the kick starter and i think all of the other holes for it are in the inside of the motor.

[400exredrider]

Originally posted by Dannys440
All over and in the motor and case are the old place for things off of the XR, there is a place for a decompressinon lever on the side of the head,there is the place for the kick starter and i think all of the other holes for it are in the inside of the motor.

i dont think thats accurate,,,im almost 99% sure but i could be wrong

[Dannys440]

here are some pics for the decompression place:

[400exredrider]

hmm,,, i never noticed

[Dannys440]

I just happend to see that last night,and i might take a pic of the inner spots if i take my case apart to replace a bolt on my clutch.

[2004exrider]

ok i got a question, if you put them on with the stock piston will you feel any kind of difference? since its only making it a 9.3:1.

[400exredrider]

nah, if you in there and going to keep it stock bore you might as well go with a std bore High comp 11:1, itll cost you from 90-140 plus gasket set is like 25 bucks.

[PHIL_B54]

Originally posted by 400exredrider
nah, if you in there and going to keep it stock bore you might as well go with a std bore High comp 11:1, itll cost you from 90-140 plus gasket set is like 25 bucks.

i love my stock bore high comp. with a cam, it is like a whole new bike.

btw...if you were able to change everything over to make your ex a kicker, the kicker would almost have to run thru your footpeg, and break lever, and it would backwards kick thru your healgaurd