310 big bore head gasket failure!!!

[bobizzle]

i have a friend who installed a big bore cylinder in a stock cylinder. ported and polished, put it on a degree wheel, port timings are right for the application we are using it for.

the question is that it keeps blowing the head gasket. had asbestos (big bore) gasket. blew it on higher rpm. got a copper one made and same thing. even coated the gasket with yamabond to try and get it to seal.

one of the head studs stripped. torqued to the proper 22lbs. just taken off and on a few times. helicoil failed.

some people were talking about o-ringing the head, but will need to insert the metal threads into the hole and will loose space needed on the sleve for o-ring.

has anyone successfully ran this setup or knows of any tricks to get it to hold the head gasket down. we cant figure out any other solutions.

also, running 55 thousandths squish. not too too tight.

[machwon]

I've done a couple with no issues thus far. Does it loose coolant out the head or pressurize the radiator?

[bobizzle]

a little drools off the edge on the cylinder. it pressurizes the radiator only when you get on it.

[machwon]

You will want to fix the stud for sure. If the bowl of the head was not machined out, you may have too much compression. This can cause the radiator to over pressurize too. You can try the optional 1.6 Kpa radiator cap off a 2000 KX 500, I use one on my 250R. You can order these from the dealer, just make sure its the optional one. The only other thing I likely do different is when I machine the head the dome part gets cut so it sits inside the cylinder. This is the way I close the squish gap rather than decking the top of the cylinder so much. That seems to help with the sealing issues as it keeps the heat a little further away from the gasket. Otherwise take your cylinder and head surfaces and lap them on a piece of granate. Hope this helps, let me know if I can help you out.

[C-LEIGH RACING]

I like the step head idea to protect the gasket.
It probably would hurt, to use an 89 CR250R head instead of the TRX one.
The CR head is thicker, so it will hold its shape better once torqued down & + it will hold more coolant & that is always good.
Neil

[265 sleeper]

I used the obestis gasket and still leaked . I thought about cutting the head to where the combustion was inside the head instead of right at the gasket . But I would have to machine my cylinder to match what I cut out the head. The head has been machined for a big bore . 192 exhuast duration squish is set right at .055 . Both head and cylinder have been laped already . I guess I just need to insert it and if it keeps blowing head gaskets I will bore out the New/old sleeve. Then insert all studs and put a new sleeve in then be able to put a stainless oring in .

[bobizzle]

i would try and insert it with the sleeve in place. dont know if it will work or not, but is better than paying some more money to a lost cause.