[Walt Fricke]

Nick - measuring bolt stretch calls for a) measuring each bolt before it is installed, b) measuring each bolt as you assemble the rod (i.e., measuring to see if you have stretched it the specified amount, or measuring it after torquing it just to have a measurement, and 3) measuring it after use when you have removed the bolt. It is this last measurement which allows you to decide whether to reuse the bolt. And reuse normally is only contemplated with super grade aftermarket bolts - Porsche claims all its rod bolts are one time use only.

So measuring a bolt now, without the information from before the engine ran, is of no use.

The weakness of the 3.2 bolts is, I think, relative. They won't withstand an over rev as well as the wider 3.0 and earlier bolts. So the reason to replace stock bolts with stronger bolts is to earn some extra margin for over revs. While in daily driving there ought not to be over revs (from money shifts), they certainly can happen. However, I don't think anyone suggests disassembling a well functioning motor just to replace the bolts with stronger ones. If you do have rods off, the super bolts don't cost all that much more than the new stock bolts you otherwise would purchase.

So the question here is: did your particular over rev cause plastic deformation of the rod bolts. That, I think, you can check for. With the pistons off, you can set your torque wrench to the factory torque value, and see if the nut moves. If it moves, that is an indication that the bolt has stretched but not elastically returned to its previous length. This is a bit tricky, as the super bolt manufacturers allow a little bit of residual stretch when deciding if you can reuse. And I'm not sure how well this would work with the torque then angle system Porsche adopted at some (not known to me) point.

A bolt which has entered the plastic zone isn't necessarily a failed bolt. Say a bolt can hold a tensile force of 100 (elastic limit), and it is designed to be installed at a tensile force of 90. That should mean that operating tensile forces up to 100 will leave the bolt fine. Let's say the plastic limit is 120, and it was subjected to a force of 110. It hasn't failed, but it is now permanently longer. It may still be able to act elastically to forces of 90, but it no longer has a clamping force of 90. Less margin. Plastic deformation of a bolt or stud leaves it longer and thinner (necked down) at some part of its length. That part thus has a smaller cross section.

When I first got a 2.7 in 1984, I didn't know any of this stuff. I twice got 1st when going for 3d on my second track event. I adjusted things and eventually got it running smoothly enough, and my lap times improved. A year or two later, though, a mechanic thought the engine was down on power, and a compression test showed low. I pulled the engine and gave the shop the heads. They found all 6 exhaust valves bent into a sort of S shape. They had sawed slots in the valve guides so the valves sort of seated themselves again. No harm to the rod bolts (but these were not the thin 3.2s), and the case only came apart after the head work because one of the replaced valves broke and dropped its head into the cylinder on the track. The crank itself was fine, though lots of other parts were not fine at all.

I think I'd proceed the same way with my 3.0 if I had bent a valve or two from a mechanical over rev. Not sure what I would do if it were a 3.2. Maybe pull the rods, inspect the bearings, plan on new super bolts, and take everything else from there and what, if anything, I saw.

If a rod bolt has too much plastic stretch, the mating surfaces will separate some with each two turns of the crank, increasing bearing clearance and reducing the oil pressure in that journal. Leads to heat, melting of the bearing surface material, and things get worse - like rod bolt complete failure. Results aren't pretty. A friend had a blockage in a crank oil passage, leading to no oil to a main bearing. When he realized something was amiss, he pitted, but after stopping the engine seized up. Rod bolts with failed bearings wouldn't hold up that long.

I'd not rely on what discussion you don't see on the Internet for a conclusion that something is not a problem when there is an engine accident (like a mechanical overrev).