GlenL

Oh! Stretchy.

dr bob

The bolts must have been more than casually tight. From foggy memory, the torque I use on the cork/composite (cork in neoprene) gasket was something on the order of 20 lbs/inch, or about 1.5 lbs/ft. with the factory bolts in clean holes and no lubrication. It just didn't take much to get the correct pressure on the gasket. Too much risks gasket distortion, squeeze out, and in extreme cases the gasket will tear as it is forced out. I use a trick little Tokiko torque screwdriver that came with a 1/4" square drive accessory for using sockets. The locking nuts would be the breakaway torque plus the 20 inch/lbs, and that starts to get a bit messy as the breakaway torque for the nuts varies after the first use. Almost worth buying a new kit of locknuts for every R&R, just so the numbers will be consistent. The issue is more acute with the silicone gasket because the tension needed is even smaller. Since the tension is so low, you really must use locknuts. But the tension number is a smaller fraction of the breakaway torque, pushing the need for a method that is more space/distance than torque/tension. Hence the feeler gauge for initial setup, then count flats so they all come up together. And the paper strips to get the clearance then clamping correct.

Adk46

The person who has used a servohydraulic materials testing machine (e.g., MTS) will think of the tightening problem as a decision between using load or stroke control. I think this is a case where stroke control is best.

You don't really care about the torque on the nuts, or even the axial load in the studs - you are aiming for a certain elastic displacement of the gasket, a certain amount of "squeeze". If we had the mythical friction-less system, we could use torque, but between the lock nuts and the low loads, we are very distant from that in this case.

How to introduce the right "squeeze"? The clever person would consult the application engineers, get the suitable displacement range required in the gasket, do a calculation from thread pitch, and do a "snug plus so many turns" operation. The snugging operation is rather delicate and tricky, however; if one nut inadvertently deforms the gasket during snugging, it will throw off its neighbors. Some of the nuts have to be moved just 1/6 turn or even 1/12 turn at a time. It would be so easy on an engine stand....

This is what the embedded hard washers in some gaskets are for - assuring a certain displacement. The cam cover bolts use this approach of assuring a certain displacement regardless of torque. The washers will, however, frustrate the person who hopes to snug up a leaking oil pan 20 years later.

Me, I used the recommended torque to get a sense of how much displacement was required, plus years of experience opening and closing jars and bottles with various seals. Then I went 'round and 'round, trying to get this displacement evenly - by feel, by eye, by instinct, by discipline not to over-tighten - no unsightly bulges! I will not claim to have done it with German precision, but it doesn't leak.

dr bob

"Stroke control" is the required method for the silicone gasket, no question. In a perfect world, the gasket would arrive with spacer sleeves at each hole, and you'd torque the bolts to keep them from falling out, knowing that the spacer maintains the correct amount of squish on the gasket.

The cork gasket -can- use a torque setup when it's brand new, the threads in the girdle and on the bolts are clean and not worn, etc. But the method involves an iterative tightening sequence that sneaks up on the desired tension. Once the cor gasket is heat-cycled a few times and exposed to oil, no easy way to tell what the correct torque number is to get the perfect amount of compression for a seal without distortion or squeeze-out.

Curt, if it seals for another 100k and the bolts don't fall out along the way, I call it good.

Kevin in Atlanta

My late mechanic instructed me to look for the cork gasket to slightly bulge. The studs without spacers and with compression nuts does slow me down.