Replace Head Studs?
02-22-2016, 10:23 AM
#211
Rennlist Member
You should ask Mike.....no stock specification will apply.
Porsche's original specifications put the fasteners (studs and bolts) into stretch, without putting them into yield. This design is extremely good, since the head gasket is "pinched" down both hot and cold. (Note that this applies to both 928 and 951 models.)
When aftermarket companies started making higher quality head stud kits for the 951 models, I tried them, of course. The aftermarket companies used the same torque specifications as the stock application, however because the material was so much better, the stock torque specifications did not stretch the hardware. It was virtually impossible to retain the head gaskets on the 951 engines, using this hardware, simply because the studs were not stretched.
To get that hardware to stretch, the torque required to get them into the required stretch was so high that the threads simply would not hold in the aluminum blocks. Many people went to 14mm hardware to increase the torque.....again, they could not get the hardware into stretch, but they compensated by increasing the torque. The 944 GTR engines used huge studs (.625")....and the heads would actually crack sometimes, when tightening them down.
Mike's a very smart engineer/machinist. I'm sure he knows exactly where his hardware needs to be torqued to apply the proper preload.
Porsche's original specifications put the fasteners (studs and bolts) into stretch, without putting them into yield. This design is extremely good, since the head gasket is "pinched" down both hot and cold. (Note that this applies to both 928 and 951 models.)
When aftermarket companies started making higher quality head stud kits for the 951 models, I tried them, of course. The aftermarket companies used the same torque specifications as the stock application, however because the material was so much better, the stock torque specifications did not stretch the hardware. It was virtually impossible to retain the head gaskets on the 951 engines, using this hardware, simply because the studs were not stretched.
To get that hardware to stretch, the torque required to get them into the required stretch was so high that the threads simply would not hold in the aluminum blocks. Many people went to 14mm hardware to increase the torque.....again, they could not get the hardware into stretch, but they compensated by increasing the torque. The 944 GTR engines used huge studs (.625")....and the heads would actually crack sometimes, when tightening them down.
Mike's a very smart engineer/machinist. I'm sure he knows exactly where his hardware needs to be torqued to apply the proper preload.
02-22-2016, 11:00 AM
#212
When you talk to him can you also get the torque process for his girdle studs? I can't seem to find it. Get him via email.
02-22-2016, 12:28 PM
#213
Rennlist Member
02-22-2016, 06:45 PM
#214
10-25-2016, 09:09 PM
#216
Neither do I, recently. I hope I have enough info to implement his flywheel and hydraulic throw out bearing mods.
10-26-2016, 10:03 AM
#217
Rennlist Member
10-26-2016, 02:18 PM
#221
Nordschleife Master
10-26-2016, 03:33 PM
#222
The part I am missing is a center shaft to use other than porsche splined disks.
10-27-2016, 10:19 AM
#223
Rennlist Member
Ah, I got you. Makes sense. Sounds like you'd have to have one machined to your specs.
11-04-2016, 11:30 PM
#224
Rennlist Member
Continued resurrection of this old thread, which I just chewed through all 15 pages of. Again.
This is directed towards Greg. Many pages ago, you made the comment that you convert the 85-86 32v engines to the later bolts. Is this across the board, or only for higher performance builds?
Later, in the write up you provided, you mentioned reusing the stock studs on 85-86 32v if they were all in good condition.
After reading about your recent work on the low mileage GTS with the atrocious head gaskets, I am starting to plan the job to replace the head gaskets and weld up the pitted heads on my 1986.5 sooner rather than later. Should I go with the stock studs if they are serviceable, or do I pull them and convert to bolts?
Engine will be coming out and live on a good stand for this work.
Thanks for your time,
Seth K. Pyle
This is directed towards Greg. Many pages ago, you made the comment that you convert the 85-86 32v engines to the later bolts. Is this across the board, or only for higher performance builds?
Later, in the write up you provided, you mentioned reusing the stock studs on 85-86 32v if they were all in good condition.
After reading about your recent work on the low mileage GTS with the atrocious head gaskets, I am starting to plan the job to replace the head gaskets and weld up the pitted heads on my 1986.5 sooner rather than later. Should I go with the stock studs if they are serviceable, or do I pull them and convert to bolts?
Engine will be coming out and live on a good stand for this work.
Thanks for your time,
Seth K. Pyle
11-05-2016, 06:29 PM
#225
Former Sponsor
Thread Starter
Continued resurrection of this old thread, which I just chewed through all 15 pages of. Again.
This is directed towards Greg. Many pages ago, you made the comment that you convert the 85-86 32v engines to the later bolts. Is this across the board, or only for higher performance builds?
Later, in the write up you provided, you mentioned reusing the stock studs on 85-86 32v if they were all in good condition.
After reading about your recent work on the low mileage GTS with the atrocious head gaskets, I am starting to plan the job to replace the head gaskets and weld up the pitted heads on my 1986.5 sooner rather than later. Should I go with the stock studs if they are serviceable, or do I pull them and convert to bolts?
Engine will be coming out and live on a good stand for this work.
Thanks for your time,
Seth K. Pyle
This is directed towards Greg. Many pages ago, you made the comment that you convert the 85-86 32v engines to the later bolts. Is this across the board, or only for higher performance builds?
Later, in the write up you provided, you mentioned reusing the stock studs on 85-86 32v if they were all in good condition.
After reading about your recent work on the low mileage GTS with the atrocious head gaskets, I am starting to plan the job to replace the head gaskets and weld up the pitted heads on my 1986.5 sooner rather than later. Should I go with the stock studs if they are serviceable, or do I pull them and convert to bolts?
Engine will be coming out and live on a good stand for this work.
Thanks for your time,
Seth K. Pyle
If they are bad....even if it is only one or two....you either have to replace them all, or find good used ones to install for the bad ones. The stud material is no.longer the same!
If you need a whole set, the current studs are so terrible, I'd suggest you use bolts.
Ever stud that you remove, you will need to chase the threads in the block. Don't use a tap, unless you absolutely have to! Use a thread chaser, instead.