head bolts
12-07-2010, 04:40 PM
#41
Ok i'm gonna let the cat out of the bag!
Take your old bolts and pick one, any one then set it up and measure its absolute length. Then torque that bolt to your spec, then remove bolt and remeasure. There it is!
Its in your hands use it as you will. If you like you can even test old bolts you didn't reuse to see what they do and at what point yield and how much it takes to ruin them completely. I warn you it takes ALOT.
Go to Mercedes for a general idea how much yeild is considered ok. Its quite a bit, I'm not going to suggest you do any of this but dam I wish I was in the LS1 bolt business.
Heat is what ruins headbolts, overheat it and they will stretch beyond MAX Yield and not hold tension causing head gasket failure.
A good example of this is poeople who don't change the coolant regularly and the heads run hot because the coolant holes are partially blocked. The head bolts relax and the head gasket fails!
I have seen people retighten headbolts after overheating the engine and get away with it believe it or not. If your headbolts come loose it because they got hot!
Take your old bolts and pick one, any one then set it up and measure its absolute length. Then torque that bolt to your spec, then remove bolt and remeasure. There it is!
Its in your hands use it as you will. If you like you can even test old bolts you didn't reuse to see what they do and at what point yield and how much it takes to ruin them completely. I warn you it takes ALOT.
Go to Mercedes for a general idea how much yeild is considered ok. Its quite a bit, I'm not going to suggest you do any of this but dam I wish I was in the LS1 bolt business.
Heat is what ruins headbolts, overheat it and they will stretch beyond MAX Yield and not hold tension causing head gasket failure.
A good example of this is poeople who don't change the coolant regularly and the heads run hot because the coolant holes are partially blocked. The head bolts relax and the head gasket fails!
I have seen people retighten headbolts after overheating the engine and get away with it believe it or not. If your headbolts come loose it because they got hot!
Last edited by O2Form; 12-07-2010 at 05:01 PM.
12-07-2010, 06:09 PM
#43
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No one except this guy reuses head bolts. Sure it might work, I have never tried. GM sevice manual has a part that says "IMPORTANT: Head bolts are NOT reuseable" in bright red letters. I don't think its because GM wants your money. Most of the Gen3/4 head gaskets we do are warranty, meaning GM buys the bolts from the dealer. If that was true, it would say to reuse them.
12-07-2010, 06:27 PM
#45
Absolutely never listen to anyone who tells you to reuse the stock headbolts in your LSx engine. That is absolutely ludicrous and is a very bad idea.
If you don't believe it do this simple test. Install one new headbolt and TQ to 22 ft pounds. Install one old head bolt and TQ to 22 ft pounds. Then, turn both the specified degrees for the first sequence. You will notably feel that difference in the bolts. You probably won't even finish the step with the old bolt, as it will feel so weak that you'll think it's gonna break. It probably won't break BTW, but is notably weaker and as such it CAN NOT perform like a new bolt would.
Alternatively, choose a TQ around 75 ft/pd. It will be harder to get the used bolt there, as it is so weak that it will stretch rather easily and prevent getting to the TQ value you are going for.
If you don't believe it do this simple test. Install one new headbolt and TQ to 22 ft pounds. Install one old head bolt and TQ to 22 ft pounds. Then, turn both the specified degrees for the first sequence. You will notably feel that difference in the bolts. You probably won't even finish the step with the old bolt, as it will feel so weak that you'll think it's gonna break. It probably won't break BTW, but is notably weaker and as such it CAN NOT perform like a new bolt would.
Alternatively, choose a TQ around 75 ft/pd. It will be harder to get the used bolt there, as it is so weak that it will stretch rather easily and prevent getting to the TQ value you are going for.
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12-07-2010, 07:14 PM
#47
Absolutely never listen to anyone who tells you to reuse the stock headbolts in your LSx engine. That is absolutely ludicrous and is a very bad idea.
If you don't believe it do this simple test. Install one new headbolt and TQ to 22 ft pounds. Install one old head bolt and TQ to 22 ft pounds. Then, turn both the specified degrees for the first sequence. You will notably feel that difference in the bolts. You probably won't even finish the step with the old bolt, as it will feel so weak that you'll think it's gonna break. It probably won't break BTW, but is notably weaker and as such it CAN NOT perform like a new bolt would.
Alternatively, choose a TQ around 75 ft/pd. It will be harder to get the used bolt there, as it is so weak that it will stretch rather easily and prevent getting to the TQ value you are going for.
If you don't believe it do this simple test. Install one new headbolt and TQ to 22 ft pounds. Install one old head bolt and TQ to 22 ft pounds. Then, turn both the specified degrees for the first sequence. You will notably feel that difference in the bolts. You probably won't even finish the step with the old bolt, as it will feel so weak that you'll think it's gonna break. It probably won't break BTW, but is notably weaker and as such it CAN NOT perform like a new bolt would.
Alternatively, choose a TQ around 75 ft/pd. It will be harder to get the used bolt there, as it is so weak that it will stretch rather easily and prevent getting to the TQ value you are going for.
12-07-2010, 07:45 PM
#48
Oh ****, here we go, lol..... 
12-08-2010, 11:14 PM
#52
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Absolutely never listen to anyone who tells you to reuse the stock headbolts in your LSx engine. That is absolutely ludicrous and is a very bad idea.
If you don't believe it do this simple test. Install one new headbolt and TQ to 22 ft pounds. Install one old head bolt and TQ to 22 ft pounds. Then, turn both the specified degrees for the first sequence. You will notably feel that difference in the bolts. You probably won't even finish the step with the old bolt, as it will feel so weak that you'll think it's gonna break. It probably won't break BTW, but is notably weaker and as such it CAN NOT perform like a new bolt would.
Alternatively, choose a TQ around 75 ft/pd. It will be harder to get the used bolt there, as it is so weak that it will stretch rather easily and prevent getting to the TQ value you are going for.
If you don't believe it do this simple test. Install one new headbolt and TQ to 22 ft pounds. Install one old head bolt and TQ to 22 ft pounds. Then, turn both the specified degrees for the first sequence. You will notably feel that difference in the bolts. You probably won't even finish the step with the old bolt, as it will feel so weak that you'll think it's gonna break. It probably won't break BTW, but is notably weaker and as such it CAN NOT perform like a new bolt would.
Alternatively, choose a TQ around 75 ft/pd. It will be harder to get the used bolt there, as it is so weak that it will stretch rather easily and prevent getting to the TQ value you are going for.
Thanks, i'm getting new bolts.
Do you have my address ?
12-09-2010, 09:30 AM
#54
Ok, this is nuts...
Do you understand WHY we use the Torque to Yield method?
It gives more clamping force, and is actually more consistant with that clamping force and weighs less.
How does it achieve these abilities?
More clamping force with a smaller and lighter bolt: Basically you are using a smaller bolt than you would have 20 years ago (non-TTY bolt) and tightening it PAST its yield point into its "Plastic Phase", When you pass the Yield point, and get to the Plastic Phase this is when the bolt will not return to its original shape and size.
More Consistent Clamping Force
When you torque using the traditional method, just to 100 ft/lb for instance The amount of clamping force you apply is Dependant on how clean and straight your threads are, is there oil on the threads etc. Now TTY gets you to a set point which is a low torque spec then has you go a predetermined # of degrees, This allows a more consistent torque because friction no longer plays a part in the final product.
So your argument all along has been...
"People seriously if the bolts were not reuseable because they were weak from being TTY then they wouldn't be holding in the 1st place."
- Wrong, you are relying on the stretch of the bolt to give additional clamping force to hold the heads, once the bolts have been torqued and relieved, the bolt is deformed and you will not get the same stretch again.
"Case in point ALL the bolts in brake systems are TTY but everyone uses them over and i've NEVER seen any fail."
-In my experience (Porsche Certified Mechanic) The reason all brake bolts are supposed to be replaced, is not due to the TTY reasoning, it is because the bolts are treaded for anti-corrosion, and also have loctite applied. I havent personally come across brake components that are TTY. And no, I dont typically replace those bolts either, just reapply loc-tite, Im already charging $2000 for brakes lets not make it and worse...
"Its a way to empty pockets of money"
-Really... Actually it isnt, Weight savings has a lot to do with it, for emissions etc vehicles need to be lighter. And before you throw the BS flag on that one... Porsche in the new Panamera is using TTY ALUMINUM bolts for just about everything in the engine, and across the body they can... I am going to attach a graph that shows the clamping force of a bolt, you will see where a typical TTY bolt is tightened to just before the Ultimate Tensile Strength of a bolt, these aluminum bolts are torqued to the UTS point, we have some $2000 torque wrench that will torque a bolt to just before that wonderful spot where it gets REALLY easy to turn... All in the name to save weight, and you watch, this will become more and more popular just give it time.
"I got other news for you...if the bolts were actually over torqued in the 1st place THEY WOULDN'T HOLD!"
-Nowhere does it say that TTY is over-torquing a bolt, your stretching it beyond its ability to return to its original shape, the only time anything is OVER-done is when you reqtorq the used bolt, you OVER-stretch it, and it becomes thinner.
"If you actually TTY the bolt is no longer as strong as it was."
Im glad to see ONE of your personalities agrees with logic
"You guys ever hear of a company called Mercedes? they use the same head bolts and allow a percentage longer that you can measure each time untill the bolts are strechted beyond SERVICE. About 3-6 times. I'm not making this up trust me. You think ARP bolts are different than the GM bolts?"
-Ok, so instead of going to the extreme that GM did for the absolute lightest bolt, and cheapest material, Mercedes went a little farther and actually did the R&D to get something that is in the middle of the compromise of weight ( Since when has Mercedes EVER been concerned about Weight) and strength, if you look at the above graph, my guess would be that the bolt would be much closer to the Yield point of the torque instread of being closer to the UTS point.
And Yes the ARP bolts are MUCH different, you are going back to the old style of overkill, get a very hard bolt and give it a set torque value, but youll also notice that they try to achieve the end result of the TTY method, because arent you supposed to use there oil, and torque and release in a number of steps? With the ARP bolt, you are never getting close to the Yield point so you dont need to worry about it. But you do need to worry about the fact that the ARP bolts are SO strong that they actually tweak the block a small amount, hence the reason you need to have the block machined for mains, and the rods machined for rod bolts (per ARP)
"Do you have any idea how BS i've swallowed in 40 years in the car industry?"
-And now we get to the root of the problem, I see it all the time, Old-timer, afraid of change, Stuck in the "Good Ol Days" Well, Things have changed and are changing, But i wouldn't get used to it if i were you, cause as soon as you do, They're just going to change again... Itll be interesting to hear your comments in a few years after GM has gone DFI with the LS series about using rubber line to the rails, itll take 1700psi no problem...
Mark
Do you understand WHY we use the Torque to Yield method?
It gives more clamping force, and is actually more consistant with that clamping force and weighs less.
How does it achieve these abilities?
More clamping force with a smaller and lighter bolt: Basically you are using a smaller bolt than you would have 20 years ago (non-TTY bolt) and tightening it PAST its yield point into its "Plastic Phase", When you pass the Yield point, and get to the Plastic Phase this is when the bolt will not return to its original shape and size.
More Consistent Clamping Force
When you torque using the traditional method, just to 100 ft/lb for instance The amount of clamping force you apply is Dependant on how clean and straight your threads are, is there oil on the threads etc. Now TTY gets you to a set point which is a low torque spec then has you go a predetermined # of degrees, This allows a more consistent torque because friction no longer plays a part in the final product.
So your argument all along has been...
"People seriously if the bolts were not reuseable because they were weak from being TTY then they wouldn't be holding in the 1st place."
- Wrong, you are relying on the stretch of the bolt to give additional clamping force to hold the heads, once the bolts have been torqued and relieved, the bolt is deformed and you will not get the same stretch again.
"Case in point ALL the bolts in brake systems are TTY but everyone uses them over and i've NEVER seen any fail."
-In my experience (Porsche Certified Mechanic) The reason all brake bolts are supposed to be replaced, is not due to the TTY reasoning, it is because the bolts are treaded for anti-corrosion, and also have loctite applied. I havent personally come across brake components that are TTY. And no, I dont typically replace those bolts either, just reapply loc-tite, Im already charging $2000 for brakes lets not make it and worse...
"Its a way to empty pockets of money"
-Really... Actually it isnt, Weight savings has a lot to do with it, for emissions etc vehicles need to be lighter. And before you throw the BS flag on that one... Porsche in the new Panamera is using TTY ALUMINUM bolts for just about everything in the engine, and across the body they can... I am going to attach a graph that shows the clamping force of a bolt, you will see where a typical TTY bolt is tightened to just before the Ultimate Tensile Strength of a bolt, these aluminum bolts are torqued to the UTS point, we have some $2000 torque wrench that will torque a bolt to just before that wonderful spot where it gets REALLY easy to turn... All in the name to save weight, and you watch, this will become more and more popular just give it time.
"I got other news for you...if the bolts were actually over torqued in the 1st place THEY WOULDN'T HOLD!"
-Nowhere does it say that TTY is over-torquing a bolt, your stretching it beyond its ability to return to its original shape, the only time anything is OVER-done is when you reqtorq the used bolt, you OVER-stretch it, and it becomes thinner.
"If you actually TTY the bolt is no longer as strong as it was."
Im glad to see ONE of your personalities agrees with logic
"You guys ever hear of a company called Mercedes? they use the same head bolts and allow a percentage longer that you can measure each time untill the bolts are strechted beyond SERVICE. About 3-6 times. I'm not making this up trust me. You think ARP bolts are different than the GM bolts?"
-Ok, so instead of going to the extreme that GM did for the absolute lightest bolt, and cheapest material, Mercedes went a little farther and actually did the R&D to get something that is in the middle of the compromise of weight ( Since when has Mercedes EVER been concerned about Weight) and strength, if you look at the above graph, my guess would be that the bolt would be much closer to the Yield point of the torque instread of being closer to the UTS point.
And Yes the ARP bolts are MUCH different, you are going back to the old style of overkill, get a very hard bolt and give it a set torque value, but youll also notice that they try to achieve the end result of the TTY method, because arent you supposed to use there oil, and torque and release in a number of steps? With the ARP bolt, you are never getting close to the Yield point so you dont need to worry about it. But you do need to worry about the fact that the ARP bolts are SO strong that they actually tweak the block a small amount, hence the reason you need to have the block machined for mains, and the rods machined for rod bolts (per ARP)
"Do you have any idea how BS i've swallowed in 40 years in the car industry?"
-And now we get to the root of the problem, I see it all the time, Old-timer, afraid of change, Stuck in the "Good Ol Days" Well, Things have changed and are changing, But i wouldn't get used to it if i were you, cause as soon as you do, They're just going to change again... Itll be interesting to hear your comments in a few years after GM has gone DFI with the LS series about using rubber line to the rails, itll take 1700psi no problem...
Mark
12-09-2010, 09:46 AM
#55
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thanks Mark, that was pretty educational. my Mech-E buddies couldn't explain this to me? what the hell do they learn but HVAC?
after leaving ship design, im trying to move to detroit and working for GM. hopefully in this move, I will learn a lot more concerning these subjects.
after leaving ship design, im trying to move to detroit and working for GM. hopefully in this move, I will learn a lot more concerning these subjects.
12-09-2010, 09:52 AM
#56
thanks Mark, that was pretty educational. my Mech-E buddies couldn't explain this to me? what the hell do they learn but HVAC?
after leaving ship design, im trying to move to detroit and working for GM. hopefully in this move, I will learn a lot more concerning these subjects.
after leaving ship design, im trying to move to detroit and working for GM. hopefully in this move, I will learn a lot more concerning these subjects.
Good luck with DET... I used to live about an hour north east of there.... Good luck... LOL
Mark
12-09-2010, 10:14 AM
#57
TECH Senior Member
My understanding (... and I found out Civil Engineers know/use this...):
Head gasket (and especially MLS type) effective sealing depends on all the head bolts having an even clamping load.
TTY head bolts are tightened cold (using the TTY procedure) to the yield point which is the start of the plastic region...
look closely at the attached diagram;
- in the elastic region, when the stress is removed, a bolt returns to its original length;
- in the plastic region, when the stress is removed, the bolt returns to a length which is longer than its original length (i.e. the bolt is now permanently longer than it was originally); the bolt has plastically deformed;
- it is harder to get all head bolts to the same clamping load in the elastic region, look at the steepness of the elastic slope, a small deviation in strain causes a large change in stress (clamping load);
- it is much easier to get all head bolts to the same clamping load in the plastic region, the slope of the curve is almost flat for a wider range of strain, deviations in strain cause no change in stress (clamping load); so as the cylinder head expands the head bolts get longer but the clamping load stays the same (the curve is flat, the plastic range); when the cylinder head contracts, the head bolts get shorter and the clamping load stays the same (still within the plastic range); this is what TTY bolts designed function is;
the problem is: when the tension on a TTY bolt is removed, the bolt does not return to its original length since it was plastically deformed (which also means the bolt material has work hardened); if this bolt is stretched again to its yield point, the plastic region is now narrower (see my next post below), and the bolt now moves further along the stress-strain curve and goes past the end of the plastic region where stress starts increasing; two things happen:
(1) since the bolts are leaving the flat plastic region there will be variations in clamping load between bolts (since each bolt's strain is slightly different than the other bolts) [which distorts the block and reduces head gasket sealing ability],
(2) riding up up the curve past the end of the plastic region brings the bolt closer to the rupture point since his raised curve also is now narrower (so the rupture point comes sooner).
So, while some people get lucky, it is a very poor idea to reuse TTY bolts.
Head gasket (and especially MLS type) effective sealing depends on all the head bolts having an even clamping load.
TTY head bolts are tightened cold (using the TTY procedure) to the yield point which is the start of the plastic region...
look closely at the attached diagram;
- in the elastic region, when the stress is removed, a bolt returns to its original length;
- in the plastic region, when the stress is removed, the bolt returns to a length which is longer than its original length (i.e. the bolt is now permanently longer than it was originally); the bolt has plastically deformed;
- it is harder to get all head bolts to the same clamping load in the elastic region, look at the steepness of the elastic slope, a small deviation in strain causes a large change in stress (clamping load);
- it is much easier to get all head bolts to the same clamping load in the plastic region, the slope of the curve is almost flat for a wider range of strain, deviations in strain cause no change in stress (clamping load); so as the cylinder head expands the head bolts get longer but the clamping load stays the same (the curve is flat, the plastic range); when the cylinder head contracts, the head bolts get shorter and the clamping load stays the same (still within the plastic range); this is what TTY bolts designed function is;
the problem is: when the tension on a TTY bolt is removed, the bolt does not return to its original length since it was plastically deformed (which also means the bolt material has work hardened); if this bolt is stretched again to its yield point, the plastic region is now narrower (see my next post below), and the bolt now moves further along the stress-strain curve and goes past the end of the plastic region where stress starts increasing; two things happen:
(1) since the bolts are leaving the flat plastic region there will be variations in clamping load between bolts (since each bolt's strain is slightly different than the other bolts) [which distorts the block and reduces head gasket sealing ability],
(2) riding up up the curve past the end of the plastic region brings the bolt closer to the rupture point since his raised curve also is now narrower (so the rupture point comes sooner).
So, while some people get lucky, it is a very poor idea to reuse TTY bolts.
Last edited by joecar; 12-16-2010 at 09:22 PM. Reason: edits
12-09-2010, 10:44 AM
#58
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I honestly believe that the main purpose of a mech-e is to make my life hell... You know whats worse than an american Mech-e??? A German one.... Oh gawd i wanna kick Fritz in the ***** sometimes...
Good luck with DET... I used to live about an hour north east of there.... Good luck... LOL
Mark
Good luck with DET... I used to live about an hour north east of there.... Good luck... LOL
Mark
12-09-2010, 02:10 PM
#59
TECH Senior Member
Ok, I talked with some ME's and they said that when a TTY bolt is reused in a TTY manner, the plastic region becomes narrower with each reuse...
this means the bolt is now starting to ride up the curve beyond the plastic region sooner as the cylinder head expands (since the plastic region is narrower), and rupture occurs when the strain is sufficiently along this curve.
this means the bolt is now starting to ride up the curve beyond the plastic region sooner as the cylinder head expands (since the plastic region is narrower), and rupture occurs when the strain is sufficiently along this curve.
