Headgasket question

[boostmaniac]

I am getting my block bored over.40 and I am just wondering if I can buy a 87mm headgasket or do I have to get a 86mm headgasket since thats gonna be the bore size?

 

[pneumo]

Cometic makes an 87mm headgasket.
It's not good to use a HG that is smaller than the bore.

 

[boostmaniac]

OK but does anyone make any 86mm gaskets? .40 over is 86mm

 

[TurboDSM90]

The first time I used a cometic, it was on a stock bore block, and resurfaced head; bad idea. It pushed coolant out the overflow at anything over 23 psi.

Second time I used a cometic HG in the HP style, I believe I used a 86 over HG(maybe 87, gotta find the receipt) . I had the head and block resurfaced to the finest R/A rating the machine shop could do (per cometics instructions) and the POS is leaking coolant into the overflow under high boost(26psi).

I gave it a second shot, and now I regret it. It was the only option for me that I could find in an oversize bore, and I regret overboring the block now too

Stick to the stock bore if possible, and an OEM HG!

Ask GRNDSM, search for his HG topic.

I am thinking about O ringing the block and/or head, but thats a whole other topic

 

[1fast97gsx]

I had the same problems with a cometic headgasket. I pushed coolant like crazy under high boost. I'd Oring the head and get an oem headgasket.

 

[pneumo]

UH-OH. I just finished putting my motor back together with a Cometic HG. I hope it holds.

 

[GRNDSM]

Cometic HG can work very well, but only when you have “mirror like” surface finish on BOTH surfaces (block and head).