I am running an 11:1 compression Wiseco piston (+.040) and with three races blew a headgasket. One headbolt had ripped the threads out of the cylinder. I helicoiled the head bolt and ripped another one out and blew another head gasket.

This time a helicoiled all head bolts which is what I should have done in the first place.

The torque value on the head is approx 33 ft/lbs, I pulled a head stud at 25lbs. Is anyone else having this problem?

Questions;
- 10mm x 1.25 mm headbolts don't provide alot of gripping force for the cylinder pressure, so how much compression can a stock cylinder take?

- I know there are people who are running 12:1 +, is there any modification necessary for the cylinder and head to accept higher compression?

- Even though there are only 4 headbolts, do the three 6mm valve cover bolts (that have virtually no torque value) provide any holding power? All three of these bolts where stripped when I disassembled the motor (I am the only owner) for the first time from the FACTORY!

Maybe it is because I have a 99 400ex that has a production number less than 500.

Thanks for the help.

 

I also had the same problem,I was running an 11 to 1 piston and on the 2nd or 3rd trip out I pulled a headbolt out and blew the gasket.I had the dealer put an insert in it and was told that usually only happens if the octane is too low and it pings,he also said that on the 400s most of the time you wont hear the pinging.Since Ive started running 112 octane I havent had any problems.

Hope this helps,Tom