keep blowing head gaskets

[critter416x]

i keep blowing head gaskets on my 400ex... i first had a 426 with stage to cam, kibble white springs, full exhaust and full intake.. so then i switched to a 416(different jug) and with the same above and with 4 new valves and it blew out in like not even 8hrs of ride time... i want to fix it and do it right this time and tired of doing head gaskets... any info will be appreciated greatly...

[tri5ron]

what compression ratio were you running with the 426 and/or the 416?
I'm betting that you were up at 12:1, 12.5:1.

maybe even running a aftermarket CDI ???

Without having any more info, I'd put money on you have a pulled stud.
(quite common on 400Ex's with high compression set-ups, on stock OEM studs).

It also sounds to me, like the bike has probably been overheated in the past,... and that means the possibility of also having a warped head.

Have you had the head resurfaced with each of your replacement gaskets?

Are you using high quality gaskets, or cheap low cost gaskets?

Are you using a service manual, when you are performing the replacements?

Are you using a Calibrated torque wrench ?

What setting are you torqueing the head to ?

Use the search feature and look up HD Studs, here in the 400EX forum. Read everything you can find on it. you will not only learn alot about your machine,... you will in all probability find your answer. There are many threads dedicated to the subject.
Every question ever imagineable reguarding HD studs, pulled stock studs, blown head gaskets, etc. has been asked and covered by many of the members here.
Do some reading, and you will find your answer.

Also,... the search function on this forum does not recognize 2 chatacter search words.
SO, to make it work, you will need to add asteriks to the search like this...

HD** Studs

hope this helps, good luck with your machine, and welcome to the forum.

[CJM]

Ron is right, HD studs and ill add you should use a good gasket set (cometic).

For my 416 11:1 build I got the best cometic gaskets and did the studs for GP.

[critter416x]

i do have an aftermarket CDI.. i follow the book and the torque specs and do it every time, i do a tear down.. i have looked at the heavy duty studs, do they do the job that every one says they do?
should i have my head milled down so it flat and smooth?

I think the 426 was 11:1 and the 416 is a 11:1..
I been using cometic and wiseco gaskets.

[CJM]

I would take the head off and take it to a machine shop and see if they say its flat or needs to be milled down a hair.

Cheap quickie way to sometimes tell is to take the thing and put it on a pc of glass-usually glass is very flat and you will be able to see immediately. But it doesnt always work.