plez tell my dad...

[exrider008]

i just bought a wiseco piston for my 400ex. i told him that i had to get an xr400 gasket because it is thiner and if fixed the compresion, he thinks that the piston may hit the valves because of the thiner gasket.
also what would happen if i ran it with a 400ex base gasket?
Thanks!

[400exrider707]

The XR gasket will not completely fix the 400ex problem but it certainly helps. I personally used a thin Cometic and I would recommend that as it is even thinner than the XR gasket. A lot of guys run No base gasket and the thin head gasket to help the problem further. It wont hit the valves dont worry pops!;) For whatever reason honda made the 400ex piston sit below the cylinder top. Who knows, but yes you can run the thin gasket. C&D can get you a thin cometic for $20, great gasket. I went through about three tusk head gaskets and then the cometic went on and never had a problem again.

[400exrules]

what gasket could get a 10.8:1 piston to 11:1?

are the thin cometic gaskets weaker then the regular cometics, or are all cometics thin?

[exrider23]

im in the middle of a rebuild too...i have to use a xr gasket or what? My kit is coming with cometic gaskets, will this be fine?

[1fst400]

I ran cosmetic thin gaskets in my motor. only had an issue once.

at one point I was running 10.8:1 comp ratio

then swaped to 12:1 ratio.

They are a good gasket.

[400exrules]

Originally posted by 1fst400
I ran cosmetic thin gaskets in my motor. only had an issue once.

at one point I was running 10.8:1 comp ratio

then swaped to 12:1 ratio.

They are a good gasket.


what was the issue....

[cals400ex]

you can run whatever gaskets you want. i ran no base gasket with a thin cosmetic flexsteel head gasket. if you want to be sure the valves do not contact the piston then put clay on the valve reliefs and put it back together. then turn the motor over using a rachet on the crank. take the valve cover, cam, and head back off and measure the piston to valve clearance (measure the clay thickness). i did this to be sure on my 450. i never did it on my 400ex.

[LT250RMan]

Originally posted by cals400ex
you can run whatever gaskets you want. i ran no base gasket with a thin cosmetic flexsteel head gasket. if you want to be sure the valves do not contact the piston then put clay on the valve reliefs and put it back together. then turn the motor over using a rachet on the crank. take the valve cover, cam, and head back off and measure the piston to valve clearance (measure the clay thickness). i did this to be sure on my 450. i never did it on my 400ex.

Dude why would you run a engine with no base gasket? thats not good for the engine

[400exstud]

Originally posted by LT250RMan
Dude why would you run a engine with no base gasket? thats not good for the engine

They probably just used a gasket maker such as permatex to seel it. Your right though, it is not the safest way to go about it.

[cals400ex]

i used hondabond on the base. we have built 4 400ex's with this stuff and never had one problem. a few of the engine builders do this too. yes, you will lose some piston to valve clearance. however you will gain squish and have a better flame travel across the top of the piston. to each his own, but i would do it again in a heartbeat.

[LT250RMan]

Originally posted by 400exstud
They probably just used a gasket maker such as permatex to seel it. Your right though, it is not the safest way to go about it.

Ya, gasket maker stuff is a crappy way to seal a crank case, i would worry about blow by.

But that just my opinion.

[400exrider707]

Originally posted by LT250RMan
Ya, gasket maker stuff is a crappy way to seal a crank case, i would worry about blow by.

But that just my opinion.

Dont question stuff you know nothing about. There is no pressure down there, and quite a few people have used hondabond or yamabond for this procedure. The idea is to get more compression. Blow by is on piston rings what does that have to do with your cylinder to case seal?

Also guys its COMETIC NOT COSMETIC!!! hahah

[LT250RMan]

oops i was thinking of a 2 stroke engine sorry man, But i would just use the stock gasket with a higher compression piston insted of gasket maker ive have bad luck wth the gasket maker stuff.

[DieselBoy]

piston closer to valves? :eek:

[400exrider707]

Originally posted by DieselBoy
piston closer to valves? :eek:


Have you ever seen the inside of a 400ex? For whatever reason honda thought it would be a good idea to have the top of the piston a few millimeters down in the cylinder at TDC. It makes no sense to me, and from what I can tell its the only quad I've seen like this.:huh

[cals400ex]

yes, pistons closer to valves....if you measure it out you will not have a problem though. i took the time to do this on my 450r. since mickey said he actually runs no base gasket with hondabond and only 1 layer of a head gasket in his bike i figured what i was running was fine. so, i did not clay check my 400ex in. we did this on a 406 wiseco, a 416 JE, a 426 ross, and a 440 ross and we have not had a problem to this day. the only problem we came across was running one layer of a head gasket.....we have had them leak oil here and there. we now just run a full 3 layered gasket, just a thin cosmetic one.

[DieselBoy]

Originally posted by 400exrider707
Have you ever seen the inside of a 400ex? For whatever reason honda thought it would be a good idea to have the top of the piston a few millimeters down in the cylinder at TDC. It makes no sense to me, and from what I can tell its the only quad I've seen like this.:huh

Yep!