oil cooler stud is pulling out

[ryan911]

Hey Pelican-ers,

Someone (probably me) has overtightened one of the oil cooler mounting nuts, and the stud is pulling out of the case when the nut is tightened.

From what I can tell it seems the stud is pressed in, since it came straight out without rotating as the nut was turned. So I tried hammering it back in, and managed to get it close to where it was when it started, without damaging it, but it still wasn't enough bite for it to stay put when the nut was tightened.

Since the case is softer than the stud, I think that means the case isn't tight enough to hold onto the stud anymore, so will replacing it with a new stud solve the problem, or will it be the same story? Are the replacement studs made oversize to account for this?

I'm sure I'm not the first person here to run into this situation, any advice?

Thanks,
Ryan

PS - I should mention that the stud in question is the most accessible on, closest to the starter. Is it possible to through-bolt it in that location?

[john walker's workshop]

it ain't pressed in. timesert time.

[chrismorse]

Hi Ryan,

Getting the torque right on all fasteners attaching to magnesium is critical because Mag is notorious / unforgiving of overtightening.

If it doesn't feel right torquing the nuts/bolts, take it apart and find out why, or you are going to experience something like what i got into with my inherited 74 911.

I was mortally afraid of the oil temps in my Dad's 74. I installed oil lines, factory t-stat and an 85 carrera cooler and shortly after that, when well warmed up, i lost all of the engine oil, (12 quarts of synthetic) in about 2 seconds at 6k rpm.

"Someone" during the cars history overtightened, (pulled) the tiny 6 mm studs on the block mounted thermostat and with all of that oil now cooler and having higher real pressure, it popped the thermostat out of the block and lost almost all of the oil - massive blue cloud behind the car.

Pulled over and called AAA

Here is a photo of the Tstat, before and after pictures.

10 years and
10K miles ago my dad paid almost 12K to get the engine rebuilt by a very reputable shop, hard telling when the "pulling" occu

So, the moral fo the story is, be very carefull with Mag

rred
, When in doupt, Helicoil or time set the stud or bolt.

Take no chances with you engines life blood - oil.
chris

[Grady Clay]

John is ‘right on’ (as usual).
The threads in the crankcase have been ‘over-stressed’ and are pulling out of the casting. They are threaded (not pressed) into the casting.

The repair is installing a Timesert, Helicoil or other suitable thread repair part.
This is normally a ‘low stress’ attachment. The failure is due to way-over-tightening in a misguided attempt to stop an oil leak.
This may have occurred way before your taking charge of the care of your 911.

“While you are there”, you might consider installing inserts in all four of the studs on the theory that if one was over-stressed, they all were.

Best,
Grady

[ryan911]

Cool, thanks for the quick responses. Sounds like I'll be shopping around for some threaded inserts tomorrow.

Anyone have the correct torque spec for those fasteners handy? I couldn't find it in the ol' haynes manual....

[ryan911]

I was tightening the oil cooler nuts to 18 ft-lbs, is this too much? If so, is it enough to break the stud free?

Thanks,
Ryan

[ryan911]

Originally Posted by chrismorse

So, the moral fo the story is, be very carefull with Mag

That's quite the carnage, hope nothing else broke from having no oil in the system?

Is that last pic after you cleaned everything up or is that before the spillage?