head gasket question

[Pipeless416]

hey guys, just a quick question. i have a cometic gasket kit that says the head gasket is xr400r 86mm. this is going to be used with an 87mm piston. i have searched and searched and some say they use the stock xr400 head gasket for 416s and some say they have used the stock 400ex head gasket... while others have said to use an 89mm gasket. which one is correct? thanks.

[honda400ex2003]

I used the stock 400ex gasket when I did mine. I would say any of them will work. the xr gasket is thinner so you get more compression to make it what the piston manufacturer actually says. The ex ones are actually alittle less. The 86mm xr will work great. Good luck, steve

[Pipeless416]

thanks for the reply steve. i think i'll just go ahead and order some new valve springs now.. that stage 2 cam makes me nervous with my 4 year old springs.

[honda400ex2003]

sounds like a good idea with a stage 2. steve

[Honda#4]

The xr will give a true 11:1 compression, but idk how much difference there is by using a xr gasket over a stock gasket with 10:8:1 compression, in my opinion you wont be able to feel a difference between the two but a dyno could prove that I guess.

[Pipeless416]

yea i'm not too concerned with compression.. i'd like to stay as far from race gas as possible, but still have the power im looking for. the reason i was asking is that i wasn't sure if the 86mm gasket would work with an 87mm piston.

[Honda#4]

Yea it should work,otherwise you can always take a layer off a cosmetic gasket, I sure like the way mine rips with the stg 2 and a port job. You would definently like your head ported for sure with a stg 2, great throttle response and the power delivery is smooth.

[F-16Guy]

The good thing about the XR gasket is that it effectively raises the deck height of the piston by lowering the head, which is a good thing with the EX engine. I think the XR set also has a thinner base gasket which helps even more. I'm sure you guys have probably read about running something like Yamabond for a base gasket, which helps even more. The only scary thing about that is the oil passage that runs from the case, through the base gasket, and up the cylinder wall. If you get sealant in the passage, it may be a problem.

[Pipeless416]

i already have a thin base gasket from the cometic kit.. the sealer method scares me as well.. though that oil passage is already blocked off because of my four stroke tech cooler :) . i think i'll try it with what i have. my piggy bank is squealing in pain.

[sc400ex_rider]

just test fit the gasket over the piston on the bench. if it dont hit your good. i have heard of people not paying attention and putting reg gaskets on big bores and it making a funny sound. good eye

[F-16Guy]

Having a tiny bit of overhang shouldn't be a problem, although it isn't ideal. The edge of the piston should never reach the top of the cylinder wall (especially with the EX engine), so contacting the head gasket is pretty much impossible. The downside is that you expose more of the gasket to the combustion process, but with the tiny amount we're talking about here (0.5mm), I wouldn't worry about it.