Head Gasket issue on Big Bore 434 DRZ

Good morning everyone,

Me and my friend both have almost the same setup for our DRZ CW big bore hotcam FCR 39 with MRD and we both seems to have the Coolant bottle that fills itself up issue.

I looked around on here and it seems from what I red that it would be a Headgasket but I will try a couple test tonight to make sure that it is.

I will let it run with the cap off and see if there's bubble and I will also make sure that that return coolant hose is not blocked or something.

Even after we leave our bike for the night 12 hours and we come back and open the cap there's a lot of pressure that comes out. I don't have coolant in my oil and I don't have oil in my coolant.

can someone let me know if I am on the right track and also if there's somehting else I can verify before I do the headgasket.

now I found a place where I live that sells the spray copper gasket and I was wondering where and wich Gasket should I get.. I know that theres a kit on ebay but for almost 50$ and was wondering if thats the right one.


also I saw on here that the head bolt should be torqued to 42 instead of 33.5 as I did from a walkthrough when I installed the Bigbore I would like to get a confirmation from someone on here.

Any advice would be also much apreciated.

thanks everyone,


The Cometic is reputable.

Yes, copper spray the night before, both sides.

Yes, the correct head bolt torque is 42.5 not 33.5, the manual is incorrect. This is probably the cause of your failure.

Thanks a lot William once again as its not the first time you help me out! :-)

I actually did 9 000 KM without any issue and thats 9000km of hard riding and I installed at the beginning of last year.

Should I only change the head gasket?

its the head gasket. running with cap off wont tell you anything. its leaking at high rpm.

As long as there are no signs of seepage at the base gasket, you can leave that alone, provided you do not break its' seal when you remove the head.

If you do pull the barrel off, leave the piston in the bore. Pull the barrel just high enough to remove the wrist pin. Be sure to use new circlips when re-assemblying.

ah ok thanks Eddie that's what I thought but I saw that in another thread so I thought why not.

thanks for clarifying.

Make sure you bleed the air out of the system or you will have boil over issues as well.

C7979 is a correct pn for a 94mm bore

... you also want to open the bleeder on the elbow at the cylinder head

thanks a lot guys..

I will read the FAQ for the coolant maintenance I guess it should cover everything on how to refill it.! :-)

thanks a lot guys!

Edited by n1d0n

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now