Tom's comment about the nut spinning in the pocket prompted me to offer up this tip for your Mac engines..... remove the locknuts that receive the cylinder head bolts and either replace them with good quality non lock type nuts or run a tap through the nuts you take out so that the "locking" effect is eliminated or reduced to a low level. Those locking nuts can take up to as much as 25 inch pounds of torque just to turn the bolt and there is no way to assure consistent torque levels from one bolt to the other even if you are using a torque wrench. With the non locking nuts you will want to torque the head bolts to 75 inch pounds. I have never had one come loose but there is no harm in using Loctite if you are worried about it. If you have a real strong lock nut you can have as much as one third of the torque going into turning the bolt rather than applying clamping force to the head gasket. After eliminating the lock nuts I never had another head gasket problem even with the flimsy little .016" aluminim gaskets on the 91 series motors. Regards, Steve O'Hara

McCulloch Kart Engines and Steve O'Hara

Spinning Head Stud Locking Nuts