Quote:

Food for thought -- the difference in thread pitch (threads per inch) is the critical item that determines what strength is left in the holes. The holes are definitely weaker by being re-threaded, but the amount the holes are weakened is a function of the difference in thread pitch between the two bolts and less to do with the 0.02 inch difference in diameter.

Think of it this way -- when the holes were originally tapped for 8 mm bolts, a certain amount of metal was removed.

Now the holes are re-tapped for 5/16". More metal is removed, now from different parts of the hole wall. Not a good situation.

You now put your 5/16" bolt into the hole and torque it. The threads are not supported completely -- if the holes have been weakened enough, the hole wall will fail before you reach the torque specification. That's probably the best thing to happen, as you will now have to bring the unit to a machine shop and have them repair the holes correctly. What is likely to happen is that the hole walls will support the torque spec, but will fail when the engine is under full load.

Why? There are gaps where the original 8 mm bolt tap had already removed metal. The RTV, or threadlock or any other additive is not going to increase the ultimate strength of the bolt in the hole. All they do is to resist the bolt from turning. However, when the load is placed on the bolt, it is straight out of the hole, the additives have no affect.

This is harder to explain than I thought, and I'd be happy to try again, but the bottom line is that I wouldn't trust your "fix".

I don't disagree with your assessment. My repair is just that, a repair. If it goes badly, I'll take it off and Helicoil the hole. THe threads were so trashed I didn't have much of a choice.

I'll admit, it's a shot. Not too much material came out of the hole, I know what you are saying about thread pitch. Essentially, if there isn't enough meat on the threads, the bolt can pull right out.

At the point I was at, there wasn't much I can do without complete dis assembly. So I took a shot. If it has to come back off, it's not that big a deal, it's external...

We'll see what happens.