Head Gasket Problems
LC Sir, the problem with blown head gaskets is resolved as follows.
After assembling engine put about 50 “EASY” miles on it. Don’t let it get to hot, then,
Remove engine from chasis, remove valve train an RE-TOURQE head gasket. This is such a pain in the ASS, virtually no one ever does it. But it works on big bore motors.
Now, when first putting the head back on, remember to oil the threads of the head bolts, oil the washer under the head bolts. This allows for less turning friction when tightening down and gives a more accurate tourqe.
When re-tourqing, loosen and retourqe “ONE” bolt at a time using the pattern listed in the shop manual.
I would retourqe a head gasket on any engine regardless of wether its a big bore or not, but in the 7s case, you have to remove the motor to do it and so most people dont.
Surely its easier to remove and retourqe, than the alternative of removing and replacing another blown gasket.
Example: on the 91-95 ZX7, standard bore is 71mm. If you go 1mm over to 72mm you can use the stock head gasket with no modifications,no problem. But if you go 2mm over to 73mm you have to “CUT” or enlarge the stock gasket. However, Cometic makes gaskets in whatever size you need. But you can cut the stock head gasket and it will work.
Most Wiseco kits come with overbore gaskets from cometic now. The 2mm over (73mm)Cosworth kits Ive used, did not come with a gasket and you had to enlargen a stock one.
Obviously you do not want the edge of the gasket to hang over the edge of the bore, 1/16 of a inch back is about right.