3.0 L stud's (PLURAL) depth

[911 tweaks]

Does anyone know if all of the studs (not bolts that screw into engine) get screwed in till they bottom out in their respective spot? (I know that the head studs need to be bottomed out in their holes)
The studs in question are: head, exhaust, front chain covers, brackets that get attached, I am probably missing a few to list.
Basically, I am re assembling the engine and on many I have to do the double nut deal to thread the studs in...some are loose and I want to loctite them in.
AND MOST IMPORTANTLY, thus the question, I dont want to start assembly to find that any studs were threaded in too deep (cant attach something) OR too much thread stickning out above the nut, thus item not being held strong enough, may be a clearance issue for something, I went and used the loctite on that one stud and I set its depth wrong and now I an sunk...
**I hope there is an easy answer for this one!!!!!!

[Eagledriver]

The headstuds are the only ones I know of that aren't bottomed out in their holes. There is a measurement for the headstuds and I think it's 115mm but that needs to be confirmed. Any stud I put in I measure to make sure enough is sticking out. Any that don't bottom out should be loctited. IMO.

-Andy

[911 tweaks]

Thanks Andy!! soooooooooooo like many things in life, I will need to address each location on an individual basis? i.e. measure the hole depth, mic up the thkns of the item to be mounted, mic up the nut, washer,...I would think (sure hope) there is some rule of thumb...maybe dia of stud x 2 or 3 for the depth to thread in the stud...if they dont go in to bottom them out.
Any engine builders out there?? (Andy, I hope I am not affending you...are you well versed in this i.e. actually had to deal with this subject? Maybe only had to deal with head studs? Maybe only exhaust studs? Please explain where your experience/ opinion is coming from.

[cstreit]

Post a picture of the studs in question... I can get some measurements for you.

[ChrisBennet]

Studs are screwed in deep enough that the threads are not exposed. I think it is a misconception that studs should be bottomed out.

"... Second, for the same reason, residual stress, in a studs is more evenly distributed than in a a bolt, resulting in a more efficient installed facter. Yes, this does mean that the common prcatice of torquing a bottomed stud into a hole is wrong - very wrong. Studs should never be forced to the bottom of their holes; they are meant to be installed finger tight. Again, in low stress applications, we often break this rule for reasons of practicality."
(Carrol Smith page 88 Nut's, Bolts, Fastener's and Plumbing Handbook)

I agree with Andy on the Loctite. I must confess I only Loctite the studs that screw in easily. Pure laziness on my part.
Interestingly, Raceware advises not to use Loctite on their 911 head studs - just put them in bare.

You don't say what year your SC engine is but if it is the flavor that has a sump plate (pre-'83?) this may be helpful.





(I have the same pictures for a Carrera if someone needs them.)

-Chris

[911 tweaks]

Chris- this is perfect!! Thanks for the pictures. Car I am restoring for a guy is an 82 targa with a 81 doner engine. I presume these measurements are the distances these studs extend beyond their mounted surface on the case half?
You wouldnt by chance have the exhaust studs #'s? I have one broken and several are at different heights off the mounted surface and a couple are loose...I am begining to hate this 'doner' engine...too much missin ***** and too much time chasin everything down...sorry for venting, I feel better now.

Any info on the other studs? Obviousley these are critical ones... how about the chain covers and anything else I am spacing on...
Would it be easier if I call you?

[ChrisBennet]

Originally posted by 911 tweeks
Chris- this is perfect!! Thanks for the pictures. Car I am restoring for a guy is an 82 targa with a 81 doner engine. I presume these measurements are the distances these studs extend beyond their mounted surface on the case half?
You wouldnt by chance have the exhaust studs #'s? I have one broken and several are at different heights off the mounted surface and a couple are loose...I am begining to hate this 'doner' engine...too much missin ***** and too much time chasin everything down...sorry for venting, I feel better now.

Any info on the other studs? Obviousley these are critical ones... how about the chain covers and anything else I am spacing on...
Would it be easier if I call you?

Yes, the measurements are the exposed length of those studs before I removed them. I don't know the exhaust stud length off the top of my head.
You can arrive at the length most Porsche studs a couple of ways:
1. Measure the thickness of the material the stud has to go through and add enough for the nut and washer. In the case of the exhaust studs measure the flange on the heat exchangers.
2. Look up the studs in the Porsche PET. A stud that is specified as "M8x45" by Porsche is actually longer than 45mm. The 45mm refers to the exposed length.

I hear you on the "donor" motor. The last motor I built arrived in boxes - with extra parts from other motors thrown in. What's life without a little challenge eh?

I'l email you my contact info in case you have questions.
-Chris