Todd951968

I suspect my head studs are screwed too deeply into the block, no not allowing the nuts to be fully fastened onto the studs (there are jut threads exposed so maybe they are on about 3/4 of the way?)

I bought the car not running and the PO attempted 2 head gasket replacements that failed so he gave up. Not sure if he messed with the studs in the first place...

What is the correct measurement of the stud when inserted into the block, from the block deck to the tip of the stud where the threads are?

951and944S

Which engine...?

16V and 8V are different.

I might have pics of height on an 8V.

T

Todd951968

Thanks, its a 2.5L 8V from 1987 924S

Tiger03447

See if Morghen can help. Seems to know his way around 924's pretty good

951and944S

Sorry, might have over promised. Pic is too blurry to see, looks like 71mm but wouldn't swear by it.

I can measure one in the morning for you though.

Alternatively, if you have a head off, just depth measure from the nut/washer land to a flat surface, add 1.5mm for head gasket plus the thickness of a head nut/washer.



T

V2Rocket

Spec is 72mm but there is tolerance

Thread height over the nut doesn't really matter as long as the full nut has threads engaged
You should get the head surfaced before reassembling.

edalenta

"Alternatively, if you have a head off, just depth measure from the nut/washer land to a flat surface, add 1.5mm for head gasket plus the thickness of a head nut/washer."

This is what I did (87 924S 2.5L NA) and RaceWare concurred. You also want to account for 2-3 full threads past the top of the nut.

Todd951968

Mine were all 2 full threads BELOW the nut before I took the head off! I checked my studs with a tape measure (I know, I will now take a more accurate measurement) and they were all in the 66mm range.

How do I back out the studs?

PaulStewart

Place 2 nuts on the stud, use the lower one to back out the stud, or use a stud puller.

GPA951s

3" from the Deck of the block. is what I go by.

Van

The 72mm is for an 8-valve, the 94mm is for a 16-valve.

951and944S

I would have looked up the data before I replaced mine in the photo above but I can’t remember where it came from....., was that from a supplement or the original manuals...?

Anyways, 71.76mm is reading on my digital calliper, I missed that one by ,24mm, or 20 thousandths....

T

Todd951968

Thanks for the info! Mine are all well below that. Is it OK to just back them out a bit to meet spec or do I need to take them totally out and put loctite on the threads?

951and944S

Why someone would have had them in beyond spec height is the concern.

Hopefully it's not the case - but you know for sure they were removed before because they are installed wrong - that the person who worked on it set that height in search of good threads.

I think I would take this opportunity to remove them, run the proper tap (you want a "blind" tap not a conventional thread tap), clean the bores/threads with a solvent and compressed air, then, when you are ready to install, make a measurement from the deck to the top of the stud with each stud just resting on the first thread to to insure that you have adequate good threads once they are installed at correct height.

Resting in the bore, before 1st thread is engaged, you should have at a minimum, 72mm + the diameter of the stud, Twice diameter is probably closer to factory thread engagement.

I use a Loctite/Permatex brand liquid teflon on those threads but I only use aftermarket studs with the hex drive feature to turn them. I have never had one turn when torquing head but in the event you did, an allen wrench can hold it.

T

500

Interestingly, the 944S 16V stays with the same 72 mm stud height as the 8V cars. I know the 94 mm is correct for the 968, but I don't know about the S2.

I just went through this exercise on my 2.5 16V rebuild for which I installed new factory head studs. The result with the head on looks perfect, with just a couple of threads visible past the top of each nut with everything torqued to spec. Originally I had that same page from the 968 workshop manual and I was expecting a 94 mm height...

Not helpful for the OP, but just putting this here in case someone with a 2.5 16V is searching this question in the future.

Thanks!