QUESTION ABOUT PREVAILING TORQUE (Wayne's Book)
 

Hi everyone,

I am at the stage of putting everything back together after having the CIS out to work through the "Common Oil Leaks" mentioned in Waynes 101 book. I am also referencing his Rebuilding Book. Here is my question:

The Oil Breather Crankcase Cover and Thermostat use M6 nuts. Torque spec listed in Waynes book is 8.1 ft-lbs (11Nm) which is correct for a regular M6 nut. However, Waynes instructs the use of M6 locking nuts so my question is should these not have a different spec to taking into account the prevailing torque of the locking nut?

This is my first time doing this, I don't want to over-tighten anything and I definitely do not want to revisit the "Triangle Of Death" again anytime soon.

What torque specs have you guys use on M6 locking nuts without having any future leaks?

Thanks

Dan

http://forums.pelicanparts.com/uploa...1582322769.jpg

Good evening,

Because you don't have any threads sticking out past the nut you most likely have no prevailing torque. The blue nylon that is crimped in the top of the nut provides the prevailing torque feature that resists loosening. I would use the 11 Nm of torque that is recommended.

Nylon locking nuts are supposed to use the same torque spec as normal nuts.

It looks to me like you should use a thiner washer under the nuts? Are those the aluminum sealing washers you are using? Did you replace those studs? Seems they should stick up far enough to work on the nylocks and the sealing washers.

Yup, there is enough thread there, it’s just not fully seated. I may need thinner washers but interesting to hear it should be the same torque. Locking nuts definitely require more torque do to the prevailing torque of the plastic lined thread but I am just unsure how much. Advice elsewhere has been an additional 1.5 ft-lbs for an M6 nut which I share here to keep it documented.

Not everything about the 964 turned out to be an improvement over earlier cars but as someone who has rebuilt a 3.2 and 3.6 I noticed the factory went to all metal M6 locknuts throughout the motor. I believe but am not positive that these are reusable.

999 084 094 02

Do Not Overtorque these little studs, especially in Mag case.
 

After I installed a Carrera cooler to handle the frightfully high oil temps, I took it to about 6500 to pass a slower car - then noticed a massive blue-white cloud behind me., looked at the oil gauge, (still had oil pressure, temp about 180), and shut it down, coasted to the side of the road. Big oil slick
After towing it to my buddy's shop, we found the thermostat POPPED UP out of the block - pulled thermostat stud threads in the mag block,
At some point in the cars life, Someone overtightened and pulled the threads.

When in doubt, helicoil it and use specified torque, especially in Mag.
Chris

You need to get at least 1 to 1.5 threads above the top of the nylocks or they are not working properly. Use a thin washer. Then torque to spec. If you really want to do prevailing torque, get a dial torque gauge and run the nut to the locking part of the nut, smoothly rotate into locking ring and read the torque. Add the torque value to the prevailing torque and you are there. IMHO, getting the thread through the nut is more important than adding prevailing torque. As previously stated you don't know what someone else has done to those studs....

The factory didn’t use nyloc nuts on the thermostat and breather. They used waves washers and plain nuts.
There is a difference between nyloc and prevailing torque.
Nyloc is a nylon seal on the nut.
Prevailing torque is a distorted nut that locks after partially destroying the threads of the stud
Bruce

IMHO both all metal and nylon are lock nuts and both provide prevailing torque if the stud is tall enough to engage the prevailing torque component. The biggest difference is that nylon lock nuts can be reused up to 5 times and all metal lock nuts can only be reused 3 times

Prevailing torque is the amount of torque it takes to turn the fastener before it bottoms out.

So when, I have read, you should add the prevailing torque to the torque value when you substitute a locking nut for a conventional nut.

SO, the question is, does Porsche in their torque spec have the prevailing torque already figured in, since nylocs are spec?

I suspect it does, since the nominal torque value for an 8mm nut should be 15 lb'ft. And the Porsche spec is 18. Maybe the engineers here will jump in and clarify.

As Bruce -above -said ....you are using the wrong nuts.
It should - and always has - only regular nuts
( i prefer 8,8 hardness) with a w.washers..all you need to do is hand tight....not too much not too little............

Ivan

[QUOTE=Trackrash;10760956]Prevailing torque is the amount of torque it takes to turn the fastener before it bottoms out.

Sorry but prevailing torque is the amount of torque required to over come the mechanic interference (nylon in this case). As previously have mentioned this should be a free running nut the prevailing torque is not included in posted values.

David

Thanks everyone. So there does seem to be a difference if option on the nuts that should be used. Factory were standard with spring (wave) washers and Wayne's book (and others) recommend the use of nylok nuts. The nylok nuts make sense to me because at the same torque they seem more secure and this is not an area that any of us want. to revisit anytime soon.

I've concluded to use a thinner washer, nylok nuts torqued to spec per M6 nuts of 8.1 ft-lbs. I'm using this both on the thermostat and rather cover nuts. If I face any leaks I will report back.

Thanks - all this advice and help was really interesting!

Notice that Nylok nuts are not used in critical fastening assemblies (e.g. con rod, crankcase, cylinder head, rocker arm; essentially any structural and/or, rotating engine part; also suspension parts. The engine thermostat is not a representative example of critical tightening. Obsess in other areas.

Whether the bolt thread engages the nylon sealant area of the nut or not, apply the recommended torque like a regular nut. The thermostat isn’t going to fall off.

Sherwood