Replace Head Studs?
06-16-2010, 05:48 PM
#16
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The head bolts on a S4 sure seem a lot tighter than that.
I know the studs are different, but it just struck me as a low number.
We have all ready had the discussion about the digital torque wrenches, not sure why I have had such bad luck with them.
I can see why that a head bolt or stud that did not stretch would not be good at all.
I know the studs are different, but it just struck me as a low number.
We have all ready had the discussion about the digital torque wrenches, not sure why I have had such bad luck with them.
I can see why that a head bolt or stud that did not stretch would not be good at all.
After years of working on these and the 944 engines, I'm used to seeing torque numbers that are 65 to about 80 ftlbs. That 105 number scares me...especially thinking about what it grows to when the engine gets hot. I envision studs pulling out of the aluminum block.
I'd initially guess that the current batch of studs has slightly different material and takes more torque to yield. I'll play around with them, while I wait for more studs to come from Germany, and see if they get "softer" with multiple torques.
I'd initially guess that the current batch of studs has slightly different material and takes more torque to yield. I'll play around with them, while I wait for more studs to come from Germany, and see if they get "softer" with multiple torques.
06-16-2010, 05:57 PM
#17
Three Wheelin'
I've always been amazed at how the Porsche studs can be tightened at such great angle amounts and not yield.
My own studs will yield before the Porsche specs. I sacrifice some to develop optimal tightening procedure per heat lot batch and it winds up being 110 or so degrees and about 105ish ft/lbs at that angle. That still allows growth over the heat range before yielding. Ideally they would be as close to yielding as possible without actually doing it when the engine is at its hottest.
About ARP etc.
Yep, I've said it before and I'll say it again. Hot rod shop big name fasteners are a tension/breakage problem waiting to happen. Generic torque instructions to cover manufacturing tolerances lead to improperly tightened fasteners. That leads to block/head breakage and head gasket problems. A fastener not tight enough is much weaker than one near it's yield point and will hammer parts.
My own studs will yield before the Porsche specs. I sacrifice some to develop optimal tightening procedure per heat lot batch and it winds up being 110 or so degrees and about 105ish ft/lbs at that angle. That still allows growth over the heat range before yielding. Ideally they would be as close to yielding as possible without actually doing it when the engine is at its hottest.
About ARP etc.
Yep, I've said it before and I'll say it again. Hot rod shop big name fasteners are a tension/breakage problem waiting to happen. Generic torque instructions to cover manufacturing tolerances lead to improperly tightened fasteners. That leads to block/head breakage and head gasket problems. A fastener not tight enough is much weaker than one near it's yield point and will hammer parts.
06-16-2010, 06:34 PM
#18
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I've always been amazed at how the Porsche studs can be tightened at such great angle amounts and not yield.
My own studs will yield before the Porsche specs. I sacrifice some to develop optimal tightening procedure per heat lot batch and it winds up being 110 or so degrees and about 105ish ft/lbs at that angle. That still allows growth over the heat range before yielding. Ideally they would be as close to yielding as possible without actually doing it when the engine is at its hottest.
About ARP etc.
Yep, I've said it before and I'll say it again. Hot rod shop big name fasteners are a tension/breakage problem waiting to happen. Generic torque instructions to cover manufacturing tolerances lead to improperly tightened fasteners. That leads to block/head breakage and head gasket problems. A fastener not tight enough is much weaker than one near it's yield point and will hammer parts.
My own studs will yield before the Porsche specs. I sacrifice some to develop optimal tightening procedure per heat lot batch and it winds up being 110 or so degrees and about 105ish ft/lbs at that angle. That still allows growth over the heat range before yielding. Ideally they would be as close to yielding as possible without actually doing it when the engine is at its hottest.
About ARP etc.
Yep, I've said it before and I'll say it again. Hot rod shop big name fasteners are a tension/breakage problem waiting to happen. Generic torque instructions to cover manufacturing tolerances lead to improperly tightened fasteners. That leads to block/head breakage and head gasket problems. A fastener not tight enough is much weaker than one near it's yield point and will hammer parts.
I agree that seems like a bunch of turning to get proper tension....and I've always questioned it. The 944 engines, which use virtually the same exact stud (and use the exact same nut) only call for two 90 degree turns. What is the difference? Virtually the same head, same block thread design, and virtually the same pieces to clamp.
In the 928 application, the studs are 12x1.5 and they get turned 270 degrees (3/4 of a revolution)....to get to the "proper" place. 1.5mm times .75=1.125=.044" of stretch. That's a whole bunch.
So you think that the new Porsche studs at 105 ftlbs. might be reasonable? When I say reasonable, I mean "won't pull the threads out of the block".
06-16-2010, 07:57 PM
#19
I'm wondering what my arp studs are at torque wise in the 89 engine. Lots of turning. How would I figure that out?
06-16-2010, 08:05 PM
#20
Former Vendor
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Well, I'd guess that you would have had to torque them. If you did the 3 stages of 90 degrees, the crankshaft would have to be pulled a couple of millimeters higher...
06-16-2010, 08:07 PM
#21
Former Vendor
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06-16-2010, 08:28 PM
#22
Three Wheelin'
It may be that the original studs were the fabled "torque to yield" type. That's a misunderstood term, internet experts think it means any fastener with angle tightening instructions but it's one that is intended to yield during tightening. You could feel that happen. The advantage is that once it has yielded it now has a broader range of stretching to allow for heat changes. Sure, the tension is much lower but it still has some. There aren't many engines that actually use that and I would think it would be mentioned in the WSM.
What about the S4 head bolts? They seem to take some unholy amount of torque, have you measured them?
06-16-2010, 08:57 PM
#24
Former Vendor
Thread Starter
I don't know, the 105 that my studs see is with a finer 1.25 pitch nut so it's tugging even more. I haven't seen any pulled threads but that is a concern.
It may be that the original studs were the fabled "torque to yield" type. That's a misunderstood term, internet experts think it means any fastener with angle tightening instructions but it's one that is intended to yield during tightening. You could feel that happen. The advantage is that once it has yielded it now has a broader range of stretching to allow for heat changes. Sure, the tension is much lower but it still has some. There aren't many engines that actually use that and I would think it would be mentioned in the WSM.
What about the S4 head bolts? They seem to take some unholy amount of torque, have you measured them?
It may be that the original studs were the fabled "torque to yield" type. That's a misunderstood term, internet experts think it means any fastener with angle tightening instructions but it's one that is intended to yield during tightening. You could feel that happen. The advantage is that once it has yielded it now has a broader range of stretching to allow for heat changes. Sure, the tension is much lower but it still has some. There aren't many engines that actually use that and I would think it would be mentioned in the WSM.
What about the S4 head bolts? They seem to take some unholy amount of torque, have you measured them?
Not sure they are torque to yield, since there has never been any instructions to replace either the studs or the head bolts, in any Porsche literature. If they were a one shot thing, they would/should mention it.
New head bolts wind up right around that 75ftlb range. I use new bolts in all my engines....found out a long time ago that used bolts were way too unpredicable.
06-16-2010, 10:12 PM
#25
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Thats your problem right there, I think. Gold yellow colored replacement studs must only be turned 90 degrees twice, not three times. 20Nm + 90 degrees + 90 degrees and leave them to that. See Service Info Tech 1983 document and correct Tech Spec Book. Its probably good idea to replace them all with similar new ones and use correct tightening method. At least this would be easy explanation for higher tq.
06-16-2010, 10:32 PM
#26
06-16-2010, 10:47 PM
#28
Administrator - "Tyson"
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Another very informative thread, thanks guys!
One thing is for sure, my next motor will use head studs by Mike Simard. Keep it simple.
The big question is, what should I use in the 944S motor I'm building
One thing is for sure, my next motor will use head studs by Mike Simard. Keep it simple.
The big question is, what should I use in the 944S motor I'm building
06-16-2010, 10:57 PM
#29
Former Vendor
Thread Starter
That's easy. Stock studs. If you want a set of ARPs...I've got great deals on used sets. Plan on disassembly to retorque.
06-16-2010, 11:05 PM
#30
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