Torque angle gauge and head bolts - Over torqued?
09-12-2007, 05:12 PM
#16
Race Director
Thread Starter
Hey van, its a stock 951 head gasket...
another thing - could the studs have stretched from 95+ ft lbs?? I am paranoid with this but I don't feel like tearing it apart once its back together
I also have a "spare" HG that I didn't use because it had a few slight "waves" along the side, has anyone else seen this on a new headgasket? the difference between the high and low points is roughly 1/2"
thanks
mike
another thing - could the studs have stretched from 95+ ft lbs?? I am paranoid with this but I don't feel like tearing it apart once its back together
I also have a "spare" HG that I didn't use because it had a few slight "waves" along the side, has anyone else seen this on a new headgasket? the difference between the high and low points is roughly 1/2"
thanks
mike
09-12-2007, 09:35 PM
#17
Drifting
I used the 90 90 method on my just finished rebuild, it is running fine. Scared the crap out of myself, as I was using a 1/2-3/8 adapter. The stud felt all funny when I was torquing it down, thought I had stripped it. I had turned the adapter into a spiral.
05-23-2010, 12:37 AM
#18
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So I'm at the point where I need to begin torquing my head down. I am a bit worried by the amount of inconsistent points of view on how to do this. I'm guessing the 15/90/90 method will end up leaving inconsistent torque specs bolt to bolt. Is this an issue? How much torque is too much? I really don't want to screw up this part. Any advice?
Bte, the 90/90 is literally turning the wrench 90 degrees right? Thanks everyone
Bte, the 90/90 is literally turning the wrench 90 degrees right? Thanks everyone
05-23-2010, 10:03 AM
#20
Race Director
Thread Starter
So I'm at the point where I need to begin torquing my head down. I am a bit worried by the amount of inconsistent points of view on how to do this. I'm guessing the 15/90/90 method will end up leaving inconsistent torque specs bolt to bolt. Is this an issue? How much torque is too much? I really don't want to screw up this part. Any advice?
Bte, the 90/90 is literally turning the wrench 90 degrees right? Thanks everyone
Bte, the 90/90 is literally turning the wrench 90 degrees right? Thanks everyone
FWIW, I did the 15/90/90 and then checked the torque on the nuts, which ranged from 70 to 90 ftlbs over the 10. What I did was just go over the same torque pattern with the torque wrench and slowly (took a few passes) brought all the nuts to whatever the highest one was set at, waiting (irrc 15 min?) between each pass just like normal.
05-27-2010, 09:39 PM
#21
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I dissagree, Lego, and I know this subject has been covered before. The torque angle method is more accurate to get a consistant clamping force on the head... Essentially, what happens, is the steel studs need to be pulled in tension so they put a compressive force on the head. By knowing the tensile strength of the steel and the diameter of the studs, we can calculate how much force would be required to "stretch" a stud, let's say, 0.5mm. (I put stretch in quotes, because this stretch is the "elastic deformation" kind, where the studs will spring back to their original shape -- or course if you exceed the stretch rating, you'll get into the "plastic (permanent) deformation" part of the curve.)
The most precise way to measure this bolt stretch is to put a dial indicator on the top of the stud while you tighten the nut with an opened wrench -- this way you can physically measure the studs ellongation while you're turning the wrench. However, you need a pretty snazzy setup to do this properly. So, the alternative is to CALCULATE the stud stretch. We know the thread pitch of the nut (and stud), so we can calculate how much nut rotation is needed to ellongate the stud. Porsche has done all of this math for us -- this is where a little trust on our part come in.
Using a torque wrench, be it beam, click or dial, isn't very accurate, because, a torque wrench really measures the FRICTION the nut is feeling. This can change do to many variables (thread interface, washer interface, lubrication, etc.), and as Mike's data suggests, the torque values can be quite different, although the stud ellongation is pretty much the same.
As you say, being as careful as possible with a torque wrench (new nuts, new washers, everything lubed, like the factory manuals originally instructed) will REDUCE the friction variables, but it is still not as precise as the torque angle method... which is why the factory manuals were updated with the torque angle method.
And Mike, congrants on getting your head back on!
The most precise way to measure this bolt stretch is to put a dial indicator on the top of the stud while you tighten the nut with an opened wrench -- this way you can physically measure the studs ellongation while you're turning the wrench. However, you need a pretty snazzy setup to do this properly. So, the alternative is to CALCULATE the stud stretch. We know the thread pitch of the nut (and stud), so we can calculate how much nut rotation is needed to ellongate the stud. Porsche has done all of this math for us -- this is where a little trust on our part come in.
Using a torque wrench, be it beam, click or dial, isn't very accurate, because, a torque wrench really measures the FRICTION the nut is feeling. This can change do to many variables (thread interface, washer interface, lubrication, etc.), and as Mike's data suggests, the torque values can be quite different, although the stud ellongation is pretty much the same.
As you say, being as careful as possible with a torque wrench (new nuts, new washers, everything lubed, like the factory manuals originally instructed) will REDUCE the friction variables, but it is still not as precise as the torque angle method... which is why the factory manuals were updated with the torque angle method.
And Mike, congrants on getting your head back on!
Most people do not account the friction losses involved when lubricants are not used, unmatched hardware or incorrect hardware are used, or the relativity (or lack there of) between clamping force and fastener load. 90ft/lbs of force on a fastener does not always equate an equal amount of clamping pressure since some of the torque is lost to the friction between the nut and stud. The nut is trying to twist the stud, not pull on it.
If you are using OE style studs, the torque to degree method is correct as it accounts for the proper elasticity of the stud to apply the right clamping force, regardless of the amount of friction on the nut and washer assembly.
If you are using aftermarket studs, you should follow the manufactures recommendations on torque yield and lubrication as the frictional losses are typically tested, accounted for, and then published per application. (Raceware and ARP provide this information in their kits)
The biggest issue with not following torque values or angle specs in an all aluminum cast block is failing the threads in the block and not the fastener. You'll pull out the threads long before you overcrush the gasket.
ADDITIONAL INFO: Use a good assembly lube on your studs. International Compound (purchased at International Truck Dealers) has been the choice of Top Fuel teams for 30 years due to it's consistent results. There is no other motorsport that tears engines down as often or requires accurate clamping loads, nor has any other motorsport spent the research dollars involved in this area. If you can't get International Compound, get a bottle of Permatex Red. By no means should you use any lube or grease with metallic compounds (anti-size, moly, gear oil, etc) as the metals and additives will produce inconsistent results.
05-28-2010, 03:26 PM
#22
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Great thread!
I just finished a valve job on my S2 cab and had issues, so this is fresh on my mind.
In the past I have always used torque. This time I decided to use an angle gauge. Why? Because the factory manual said to. Why did they say to do this? I do not know. But I do know that while the factory manual gives a torque angle, it does NOT give a torque value. So I kinda had to. I also had to buy a new tool, which is always good motivation for me.
Now to my issue. While torqueing the head, most of the studs torqued the 60/90 (per the factory manual for a 90 S2) degree pulls consistent and even with no issue. BUT...on some I could litterally feel a "give" like the stud suddenly stretched.
I did not replace the old studs (did read posts on this topic and yes I understand some say always replace for good reason, just did not understand the reason). I did not replace the studs because I read that they can be a B*TCH to remove. I did not want to bugger up one, and have to pull the block to give to a machine shop to repair. But now I am concerned. I am concerned that some studs actually had a structural failure. Perhaps the torque angle method stretches the studs very close to their limits (to maximize clamping force, the accuracy Van notes). And that once stressed to their limit from the original "stretch", a "second stretching" (torque angle) can cause them to pull like taffy.
If you do much work on cars, you know you can stretch a bolt (overtorque) until it snaps. This is why torque wrenches were invented. Did the torque angle method cause this issue, if it is indeed an issue on the S2? Would the torque method have limited this issue?
At this point, my theroy is that if you choose to use the angle gauge method, do not use head studs that have been previously stretched. Replace the stud so the stud will perform (stretch) as the manufacturer intended. If you choose to reuse the old head studs, use the torque method. Thoughts?
There is another issue that I have been contemplating about torque angle. In the old days the proper proceedure after head removal and replacement was to re-torque the head after 500 miles of use. Also a major service tune up (30k miles) involved a re-torque of the head. How can you re-torque a head using the angle gauge? Do you have to loosen the head bolts and start over? Will this create issues with the studs being already "stretched" once?
On this topic, I think I would side with Legoland. Could I stretch a head stud using the "torque" method on a NEW or USED head stud? I think unlikley. Would I get the absolute most accurate and therefore the most clamping force by using a NEW stud with "torque angle"? Perhaps not. Is the difference between the two worth the risks I ponder? Perhaps in the case Marky notes, where Porsche has designed a suspension piece that needs to get that maximum torque from a bolt or the suspension part flys off of the car.
Legoland, Van & Marky all have very solid arguments. Can differing arquments be equally true, given differing circumstances. I would say yes. Just as water can exist as a gas, liquid or a solid. One person says you CAN walk on water (solid), another says you can NOT walk on water (liquid). Both are equally true. Know your circumstances.
At the 500 milestone, I plan to pull the valve cover on the S2 and check the head bolts using the torque method. Which brings up another point, with the factory manual only giving a "torque angle", what is the proper "torque"? Is it 90 ft/lbs for a S2, as Lego mentions?
Hopefully the re-torque will put my mind at ease and I will again be able to sleep at night and not worry about the wifes car. I dread the alternantive.
I just finished a valve job on my S2 cab and had issues, so this is fresh on my mind.
In the past I have always used torque. This time I decided to use an angle gauge. Why? Because the factory manual said to. Why did they say to do this? I do not know. But I do know that while the factory manual gives a torque angle, it does NOT give a torque value. So I kinda had to. I also had to buy a new tool, which is always good motivation for me.
Now to my issue. While torqueing the head, most of the studs torqued the 60/90 (per the factory manual for a 90 S2) degree pulls consistent and even with no issue. BUT...on some I could litterally feel a "give" like the stud suddenly stretched.
I did not replace the old studs (did read posts on this topic and yes I understand some say always replace for good reason, just did not understand the reason). I did not replace the studs because I read that they can be a B*TCH to remove. I did not want to bugger up one, and have to pull the block to give to a machine shop to repair. But now I am concerned. I am concerned that some studs actually had a structural failure. Perhaps the torque angle method stretches the studs very close to their limits (to maximize clamping force, the accuracy Van notes). And that once stressed to their limit from the original "stretch", a "second stretching" (torque angle) can cause them to pull like taffy.
If you do much work on cars, you know you can stretch a bolt (overtorque) until it snaps. This is why torque wrenches were invented. Did the torque angle method cause this issue, if it is indeed an issue on the S2? Would the torque method have limited this issue?
At this point, my theroy is that if you choose to use the angle gauge method, do not use head studs that have been previously stretched. Replace the stud so the stud will perform (stretch) as the manufacturer intended. If you choose to reuse the old head studs, use the torque method. Thoughts?
There is another issue that I have been contemplating about torque angle. In the old days the proper proceedure after head removal and replacement was to re-torque the head after 500 miles of use. Also a major service tune up (30k miles) involved a re-torque of the head. How can you re-torque a head using the angle gauge? Do you have to loosen the head bolts and start over? Will this create issues with the studs being already "stretched" once?
On this topic, I think I would side with Legoland. Could I stretch a head stud using the "torque" method on a NEW or USED head stud? I think unlikley. Would I get the absolute most accurate and therefore the most clamping force by using a NEW stud with "torque angle"? Perhaps not. Is the difference between the two worth the risks I ponder? Perhaps in the case Marky notes, where Porsche has designed a suspension piece that needs to get that maximum torque from a bolt or the suspension part flys off of the car.
Legoland, Van & Marky all have very solid arguments. Can differing arquments be equally true, given differing circumstances. I would say yes. Just as water can exist as a gas, liquid or a solid. One person says you CAN walk on water (solid), another says you can NOT walk on water (liquid). Both are equally true. Know your circumstances.
At the 500 milestone, I plan to pull the valve cover on the S2 and check the head bolts using the torque method. Which brings up another point, with the factory manual only giving a "torque angle", what is the proper "torque"? Is it 90 ft/lbs for a S2, as Lego mentions?
Hopefully the re-torque will put my mind at ease and I will again be able to sleep at night and not worry about the wifes car. I dread the alternantive.
Last edited by Bill; 05-28-2010 at 04:03 PM.
05-28-2010, 04:32 PM
#23
Rennlist Member
Truthfully, I think it's more important that they all be torqued as closely as possible to each other (whichever method you choose).
Having all at 75 ft/lbs is probably better than having two at 80 ft/lbs and the rest at 105 ft/lbs.
As for "retorquing" - I think you're asking for trouble, because you'll have to take the nuts all of the way off to re-lube the threads and washers to have a somewhat "controlled" environment.
Also, keep in mind the circumstances... It's great to measure bolt/stud elongation in the controlled environment of a race engine shop. When a bunch of us changed the head gasket in a field in Ohio to finish a 24 hour race, it was "grab the torque wrench and torque it down to something!!"
Use whichever method is appropriate to your goals and situation. Just fixing a blown HG in a NA car to sell? Grab the torque wrench! Building a race-ready motor that will put out 400 HP? Use torque angle...
Having all at 75 ft/lbs is probably better than having two at 80 ft/lbs and the rest at 105 ft/lbs.
As for "retorquing" - I think you're asking for trouble, because you'll have to take the nuts all of the way off to re-lube the threads and washers to have a somewhat "controlled" environment.
Also, keep in mind the circumstances... It's great to measure bolt/stud elongation in the controlled environment of a race engine shop. When a bunch of us changed the head gasket in a field in Ohio to finish a 24 hour race, it was "grab the torque wrench and torque it down to something!!"
Use whichever method is appropriate to your goals and situation. Just fixing a blown HG in a NA car to sell? Grab the torque wrench! Building a race-ready motor that will put out 400 HP? Use torque angle...
05-28-2010, 11:17 PM
#24
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it is my understanding the angle method is used primarily with clamping gaskets...
if you snug everything down intially to ~ the same torque then do 2 angles, you can rest assured the gasket is compressed to the same thickness all around...
you know the pitch, you know the initial distance (basically gasket thickness), so you know the final distance (initial thickness - 180/360 x pitch)...
imo this even compression is more important than the actual torque value in this case, in fact they may differ, but the gasket is still compressed evenly because it is the same thickness all around...
the point is torquing everything to the same value may not compress the gasket evenly unless everything is perfectly symetrical...it's not, water passages, various spacings, etc.
to get to 90 lb ft on one bolt may take 3/4 turns from snug, on another 1.25, resulting in the gasket being compressed unequally, ie, different thicknesses
one purpose of the gasket is to make up/smooth out/seal any imperfections in the surfaces...
if you snug everything down intially to ~ the same torque then do 2 angles, you can rest assured the gasket is compressed to the same thickness all around...
you know the pitch, you know the initial distance (basically gasket thickness), so you know the final distance (initial thickness - 180/360 x pitch)...
imo this even compression is more important than the actual torque value in this case, in fact they may differ, but the gasket is still compressed evenly because it is the same thickness all around...
the point is torquing everything to the same value may not compress the gasket evenly unless everything is perfectly symetrical...it's not, water passages, various spacings, etc.
to get to 90 lb ft on one bolt may take 3/4 turns from snug, on another 1.25, resulting in the gasket being compressed unequally, ie, different thicknesses
one purpose of the gasket is to make up/smooth out/seal any imperfections in the surfaces...
05-29-2010, 01:15 AM
#25
Truthfully, I think it's more important that they all be torqued as closely as possible to each other (whichever method you choose).
Having all at 75 ft/lbs is probably better than having two at 80 ft/lbs and the rest at 105 ft/lbs.
As for "retorquing" - I think you're asking for trouble, because you'll have to take the nuts all of the way off to re-lube the threads and washers to have a somewhat "controlled" environment.
Also, keep in mind the circumstances... It's great to measure bolt/stud elongation in the controlled environment of a race engine shop. When a bunch of us changed the head gasket in a field in Ohio to finish a 24 hour race, it was "grab the torque wrench and torque it down to something!!"
Use whichever method is appropriate to your goals and situation. Just fixing a blown HG in a NA car to sell? Grab the torque wrench! Building a race-ready motor that will put out 400 HP? Use torque angle...
Having all at 75 ft/lbs is probably better than having two at 80 ft/lbs and the rest at 105 ft/lbs.
As for "retorquing" - I think you're asking for trouble, because you'll have to take the nuts all of the way off to re-lube the threads and washers to have a somewhat "controlled" environment.
Also, keep in mind the circumstances... It's great to measure bolt/stud elongation in the controlled environment of a race engine shop. When a bunch of us changed the head gasket in a field in Ohio to finish a 24 hour race, it was "grab the torque wrench and torque it down to something!!"
Use whichever method is appropriate to your goals and situation. Just fixing a blown HG in a NA car to sell? Grab the torque wrench! Building a race-ready motor that will put out 400 HP? Use torque angle...
05-29-2010, 02:09 AM
#26
Under the Lift
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Hey, just noticed this old thread. We basically share the same heads and gaskets on the 928. We use the torque angle method, with bolts at least, and it ends up at about 130 ft lbs if you check the torque. Works fine, but, yes, that last 90 degrees is a struggle using a long bar. We took apart one motor that had leaking head gaskets from the day another shop assembled it and found almost all the bolts could be removed at 60-80 ft-lbs. That's apparently not enough. We do not torque-retorque unless we are using Cometic multilayer gaskets. Those compress like crazy on first torque and the bolts end up loose as a goose but snug up nicely on retorque, still using the torque angle procedure as the WSM prescribes. These bolts can take it.
Mike your car looks sweet..and fast. I saw your offer of a ride trade (temporary) on the 928 forum. Somebody should take you up on that for sure.
Mike your car looks sweet..and fast. I saw your offer of a ride trade (temporary) on the 928 forum. Somebody should take you up on that for sure.
