Head stud torque question....
#1
Thread Starter
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After reading many threads on the subject... I'm just confused. I'm using a 5L block with studs (yellow ones) and 16v heads.....
do i do the,
15 ft lbs
90 degree
90 degree...
or do i do another 90 degree?
do i do the,
15 ft lbs
90 degree
90 degree...
or do i do another 90 degree?
#2
Former Sponsor
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I do 2 90's. I tried to do 3 90's on an engine into which I had installed brand new studs and "yielded" about 80% of the studs. (I have a torque wrench that angle torques and then tells you, after you are done with that angle, what the resulting foot pound reading actually is. I actually had less torque on 80%of the fasteners after 3 90's than I had at 2 90's. Carefull inspection of the studs showed that they were actually "necked down" in the middle....yielded....junk.)
Thinking that Porsche must always be correct in what they print, I figured I had done something wrong, so I bought another brand new set of studs and repeated the same process.
Again, about 80% of the studs had yielded and were "significantly longer" than when they started.
I looked carefully, through all of the Porsche literature and noticed than none of the other models (944/951/968) ever used more than two 90's...even though the hardware, head, and block are virtually the same. I also found literature with the instructions to only do 2 90's on the 928 models.
I bought another set of studs and torqued them to 2 90's. Been doing that, ever since, and regardless of what anyone thinks or says, believe that to be the correct proceedure.
As an interesting side note to this.....I've do quite a bit of research into this "problem". ("Research", for me, means that I study the problem first hand....I don't go to the internet and see what other people think.) I've found that "old/used" studs are much stiffer....they seem to loose their elasticity with age. (Note that this is also true of the vehicles equiped with head bolts....they do not "stretch" as much when they are "old".) Most of the "older" studs (now most all 30 years old) seem very happy with 3 90's....however the "resulting torque values" are very high (sometimes over 120 ft lbs.) and I'm concerned that the threads in the block will "pull" with "initial" torque values this high, once the engine gets hot. I also believe that the design of the studs are such that Porsche wants the stud to "stretch", but not yield. I believe that a stud that is "stretched" puts better "crush" on the head gasket throughout the entire heating cycle than an "unstretched" stud. (Which is why I believe that the ARP hardware doesn't work...it is too high of a grade to properly stretch and provide the proper "preload" to the head gasket.)
The result of my research makes me install new studs in virtually all of these very old engines...and makes me buy new head bolts for the engines that use them.
Thinking that Porsche must always be correct in what they print, I figured I had done something wrong, so I bought another brand new set of studs and repeated the same process.
Again, about 80% of the studs had yielded and were "significantly longer" than when they started.
I looked carefully, through all of the Porsche literature and noticed than none of the other models (944/951/968) ever used more than two 90's...even though the hardware, head, and block are virtually the same. I also found literature with the instructions to only do 2 90's on the 928 models.
I bought another set of studs and torqued them to 2 90's. Been doing that, ever since, and regardless of what anyone thinks or says, believe that to be the correct proceedure.
As an interesting side note to this.....I've do quite a bit of research into this "problem". ("Research", for me, means that I study the problem first hand....I don't go to the internet and see what other people think.) I've found that "old/used" studs are much stiffer....they seem to loose their elasticity with age. (Note that this is also true of the vehicles equiped with head bolts....they do not "stretch" as much when they are "old".) Most of the "older" studs (now most all 30 years old) seem very happy with 3 90's....however the "resulting torque values" are very high (sometimes over 120 ft lbs.) and I'm concerned that the threads in the block will "pull" with "initial" torque values this high, once the engine gets hot. I also believe that the design of the studs are such that Porsche wants the stud to "stretch", but not yield. I believe that a stud that is "stretched" puts better "crush" on the head gasket throughout the entire heating cycle than an "unstretched" stud. (Which is why I believe that the ARP hardware doesn't work...it is too high of a grade to properly stretch and provide the proper "preload" to the head gasket.)
The result of my research makes me install new studs in virtually all of these very old engines...and makes me buy new head bolts for the engines that use them.
#5
Thread Starter
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well did the 25ft first, then 90, then 90. some were seemed tougher then others, but i got no washer spin (marked them).
so I'm done? or do i wait an hour and do the 1/4 turn loose, then re do it?
so I'm done? or do i wait an hour and do the 1/4 turn loose, then re do it?
#6
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As for torque readings, I've seen them all over the map so I've stuck with the 20nm/90/90/90 for studs and 20nm/90/90 for bolts.
#7
Rennlist Member
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Excellent timing for this post, and great info and insight as well, thank you.
I picked up new studs for the 86.5 eng refresh and a digital torque / angle wrench from Eastwood.
When setting the studs into the block I'd seen a light coat of oil is recommended by some, is that true?
Thank you,
Dave k
I picked up new studs for the 86.5 eng refresh and a digital torque / angle wrench from Eastwood.
When setting the studs into the block I'd seen a light coat of oil is recommended by some, is that true?
Thank you,
Dave k
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#8
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We are talking about your 16v 81 right
If so My WSM from Porsche Canada shows
As follows
16 valve
Nm /ftlb
1st step 20 / 14
2nd step 50/ 36
3rd step 90/65
Or
1st step 20nm/2ftlb?? ( I think this is a typo)
2nd step 90deg torque angle
3rd step 90 deg torque angle
Up to model year 84
then
32 valve
1st step 20nm/14 ftlb
2nd step 90 deg torque angle
3rd step 90 deg torque angle
No mention of a 4th step anywhere
Interesting that in 77 before the wsm were printed they spec 61.5 ftlb wait ½ hour then retorque to 61.5 ftlb
Last edited by waynestrutt; 04-17-2012 at 09:33 PM. Reason: fix