Help! my nuts are stuck..

[smallspeed]

looking for some tips/tricks/advice on "releasing my nuts"! I'm sure this is a Porsche issue sometimes too (possibly worse given the head temps) so hopefully someone has a good tip..

Basically I was helping a mate tart up his kids car - we removed the exhaust manifold, and the damn studs came out with the nuts on (like a bolt effectively). to get the thing back together properly, you really need to screw the studs into the head, then torque the nuts down onto the manifold. putting them back in again like bolts won't get the right seal to the head (and worse, might strip the threads in the head)
The nuts are the deformed thread locking type and I don't really want to screw the studs up getting them off, otherwise i'd just crank them into a vice. we have replacement nuts (they were about £4 a set) so its really the studs we want to save, as they're M7 and not cheap! (not for a 17yr old kid anyway)
I've tried WD40, tried freeze/unlock, tried soaking them in petrol over the weekend - no dice.. the only other thing I can think of is heat, but I'm waiting for the petrol to evaporate fully before trying that!

I know the "right" way to do this is replace the studs, but if we can avoid spending £60 on a set that would be nice! they're not stretch-studs or anything so are re-usable, assuming you can get the damn nuts off. Any wonder-cures, old wives tales, or urban myths for relieving stuck nuts (relevant or otherwise) greatly appreciated before I set fire to half the garage

[johnM]

Heat would be the way to go. If that fails you can carefully saw across the nut down to but not touching the stud threads. That will release the tension between the nut and stud and should then wind off.

[fetuhoe]

Sounds painful -

What type of prevailing torque nut have you used?

Clearly the torque needed to undo the nut is greater than the torque to loosen the stud hence your problem.

The question is whether this is due to corrosion or just they type of nut you have used.

The 'copper' plated prevailing torque nuts commonly being sold are a real PITA and are tricky and they lock up and are always a problem.

There are some Simmonds Silver Plated Stainless Steel K-Nuts which are very good but expensive.

I don't see why screwing them in as bolts should be a problem as the preload for a given torque doesn't change so they should work.

I would try to put them back into the holes they came out of to make sure that they don't bottom out but as long as the threads aren't damaged they should work.

[smallspeed]

there's a difference in terms of load on a thread between a stud and a bolt - the rotational movement of the thread under tension (ie dynamic load of a bolt) gives a lot more potential to do damage vs. a static stud which is being pulled against the threads (ie static load). hence a lot aluminium heads/blocks use studs rather than bolts, particularly for things like cam carriers where the threads are comparatively small

the studs are installed bottomed out into a blind threaded hole from the factory and then the nuts installed to a torque - the studs have like a non-threaded length (maybe 3mm long) which bottoms out into the hole and they're supposed to be installed to "hand tight" (whatever that is). I had thought about just shoving some washers under them to space them up a bit, but I don't want to strip the threads or anything daft in the head and have to helicoil it as that will be a right PITA!

They're steel studs and copper coated k-nuts (supposedly to stop this issue happening), but they're 15yr old and well-and-truly stuck - every single stud came out with the nut!

We may yet have to buy some new studs, but I will wait for the petrol to evaporate and give the blowtorch a try

[fetuhoe]

I am not really sure about what you mean by a dynamic versus static load.

I can agree that tightening a bolt tends to produce some twisting and this will mean that the relationship between preload and torque will not be quite as good as when using a stud but this can't really be described as dynamic loading.

I can understand why you wouldn't use this procedure with either a head stud or a main bearings stud as the twisting forces are different and torque application using a stud normally results in a more consistent preload but many engines run very well with bolted cylinder head joints.

I don't think exhaust flanges are that fussy and by using a 'K' Nut the relationship between torque and preload has lost any accurate correlation.

If you tighten the 'shoulder' of the stud into the top of the threaded hole then I agree that you can easily damage threads so using a washer would help to avoid this potential problem.

A bolt of the correct length avoids this problem completely and this is effectively what you would be doing.

I would doubt that you could bottom the stud into the end of a blind hole as the last couple of threads are never fully formed so it will be difficult to make them reach the bottom without some thread damage.

We do make cylinder head studs with a 'dog point' so they can be tightened into a blind hole without causing this problem but again this seems a bit unnecessary for an exhaust flange.

It is normal practice to make the thread that fits into a blind hole with a better 'fit' to avoid the problem with the unscrewing

A 911 exhaust stud typically has 4-5mm clearance between the end of the hole and the end of the stud.

The copper plated flange nuts that are now commonly sold are quite poor in terms of fit and I don't believe that they are an Alcoa/Simmonds product and the tolerances are all over the place.

[jackstowers]

Lock two nuts together on the head end of the stud and hold this in the vice. Apply a little heat to the nut to be removed and bingo!

[Alan @ CanfordClassics]

Or just send me your address and I will send you some new/good used studs.

If it helps email scott@canfordclassics.co.uk and he will help straight away.

HTH

Alan