Retorquing Cylinder Heads?
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From: Kingsport, TN
Retorquing Cylinder Heads?
How common of a practice is this in performance buildups? How much clamping force is lost (if any) after heat cycling? I assume it would make a difference if you had iron or aluminum heads as well too. Can anybody shed some light on this?
Last edited by Loadre; Aug 3, 2004 at 05:33 PM.
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From: Seattle, WA
Re: Retorquing Cylinder Heads?
Good Question. ARP reccomends cycling your studs/bolts 5 times in an effort to burish the treads sufficiently (and maybe "pre-set" the bolts?).
Regardless of the method you use for torquing bolts (torque wrench or torque-angle) you will have different torque numbers to shoot for depending on the lubricant used (i.e. dry > oil > sealant torque numbers... all for the same amount of bolt stretch, which is where the clamping force is actually coming from).
If the bolts were properly cycled, and at the time torqued to spec, I'm not sure what torque spec you'd use after a few heat cycles. Would the oil or other lubricant be cooked dry? would the sealant be set up and more diffucult to turn? I imagine you'd have to re-torque to a higher number at that point, but I've never heard of anyone doing so.
Just re-torquing to the final torque spec shouldn't hurt anything (probably won't even move the thing as any lube you had the first time will probably be less effective now)... but if it does move (i.e. it loosened up sufficiently) I might be worried how that happened at all.
Hopefully some of the pros here will help out on this one.
Should we just use the orginal torque spec as we did during assembly? or should the torque values/pattern change at all when checking say 500 to 1000 miles down the road?
Regardless of the method you use for torquing bolts (torque wrench or torque-angle) you will have different torque numbers to shoot for depending on the lubricant used (i.e. dry > oil > sealant torque numbers... all for the same amount of bolt stretch, which is where the clamping force is actually coming from).
If the bolts were properly cycled, and at the time torqued to spec, I'm not sure what torque spec you'd use after a few heat cycles. Would the oil or other lubricant be cooked dry? would the sealant be set up and more diffucult to turn? I imagine you'd have to re-torque to a higher number at that point, but I've never heard of anyone doing so.
Just re-torquing to the final torque spec shouldn't hurt anything (probably won't even move the thing as any lube you had the first time will probably be less effective now)... but if it does move (i.e. it loosened up sufficiently) I might be worried how that happened at all.
Hopefully some of the pros here will help out on this one.
Should we just use the orginal torque spec as we did during assembly? or should the torque values/pattern change at all when checking say 500 to 1000 miles down the road?
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From: In a house by the bay
Re: Retorquing Cylinder Heads?
Originally Posted by Loadre
How common of a practice is this in performance buildups? How much clamping force is lost (if any) after heat cycling? I assume it would make a difference if you had iron or aluminum heads as well too. Can anybody shed some light on this?
Out of safety sake, I've always retorqued. Just make sure you do it with a fully cooled engine.... especially if it has an aluminum block and/or head. As for torquing, lubricants, etc.. check with the manufacturer.
-Mindgame
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Re: Retorquing Cylinder Heads?
Originally Posted by 1racerdude
If you are using studs you need to set up a dial indicator and do the bolt stretch method.
Mindgame- you hit it on the head with the gasket. You've reminded me of a lesson I learned YEARS back in the Coast Guard... I helped with a cylinder head R&R on a V-16 diesel and after we fired the engine back up I asked the Engineering Chief about a retorque after the engine cooled. His reply was to laugh at me since this engine used no head gasket therefore no retorque was required.
Steve...
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From: LA (lower Alabama)
Re: Retorquing Cylinder Heads?
You make you a metal plate that attatches to the valve cover bolts,this does the top bolts and another plate that attatches to the plug wire holder bolts in the block and this does the bottom row, and proceed.In the case of center bolt cover's you attatch the plate to the end of the heads.If you use the bolt streach method there is no need to retorque,the bolts are way tighter than the torque spect method by 20-25 foot lbs. and the bolt is at max clamping force and stretch.
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From: In a house by the bay
Re: Retorquing Cylinder Heads?
LR,
Where are you finding specs for head stud stretch? What are we aiming for here and where are the sources. Obviously it's going to change with different diameter studs...ie, different engines.
Thanks.
-Mindgame
Where are you finding specs for head stud stretch? What are we aiming for here and where are the sources. Obviously it's going to change with different diameter studs...ie, different engines.
Thanks.
-Mindgame
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From: LA (lower Alabama)
Re: Retorquing Cylinder Heads?
MG,
As I stated earlier when using studs that if you use the stretch method I have found no need to retorque,especially when using Fel Pro gaskets.
I have a Starret electronic dial indicator that was a lab instrument. It can measure .00005 if set to do so.I mounted the sending unit on a magnetic holder and that is what I use for bolt or stud stretch.
Take a set of ARP rod bolts and pull them to spect stretch,you will find that the torque is at least 15 foot lbs more than ARP's torque spect for the same bolt.
This is why I use this method,because the bolt and nut or stud is to it's max yield point and clamping force.When I questioned ARP about this and them not putting the torque values as high as the stretch values,they said it was due to the different compaction values that a bolt has v a stud,ie what the head is made of how many threads the block has, the gasket material,etc.
As I stated earlier when using studs that if you use the stretch method I have found no need to retorque,especially when using Fel Pro gaskets.
I have a Starret electronic dial indicator that was a lab instrument. It can measure .00005 if set to do so.I mounted the sending unit on a magnetic holder and that is what I use for bolt or stud stretch.
Take a set of ARP rod bolts and pull them to spect stretch,you will find that the torque is at least 15 foot lbs more than ARP's torque spect for the same bolt.
This is why I use this method,because the bolt and nut or stud is to it's max yield point and clamping force.When I questioned ARP about this and them not putting the torque values as high as the stretch values,they said it was due to the different compaction values that a bolt has v a stud,ie what the head is made of how many threads the block has, the gasket material,etc.
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From: In a house by the bay
Re: Retorquing Cylinder Heads?
Larry,
I've been all through ARP's catalog and have never seen stretch information for anything other than rod bolts. Sure, there are "general" torque specs for different types of bolts with either ARP lube or 30W oil, but nothing on stretch of the head stud itself. Nor anything for stretch of other critical fasteners like main studs. Throw me a bone here... what are you typically seeing for stretch on a SBC head bolt? I'd like to work backwards and see what it equates to in clamping load.
ARP also mentions that rod bolts are unique in their clamping loads, for obvious reasons, where as other bolts are not and thus do not require such precision tightening methods.
Back to head stud stretch... how are you going about it? I can't find specs.. so I'd assume that you are checking the stud prior to torquing, then torquing the nut to required spec and remeasuring? Are you using TTA or just a torque wrench? Are you cycling the threads?
Checking torque with an already stretched-to-spec bolt (your ARP rod bolt stretch example) isn't really telling you much. There's an old rule of thumb that suggest a 90/10 relationship for fasteners, where 90% of the force applied is countering friction and 10% is used to stretch the bolt. So it's obvious that the type of lubricant used plays a big part on torque specs as measured with a torque wrench. Cycling the threads applies in the same way. So, unless you duplicate the original procedure to the letter... your results are going to differ. Not that it matters too much cause you're after the end result (the proper stretch).
On the head gasket and retorque... I think it still depends on the gasket. Some don't require it and others do. Has really nothing to do with the method of torquing or how much load you place on the fastener. Some gaskets just loose a little compressed height after a heat cycle or two.
-Mindgame
I've been all through ARP's catalog and have never seen stretch information for anything other than rod bolts. Sure, there are "general" torque specs for different types of bolts with either ARP lube or 30W oil, but nothing on stretch of the head stud itself. Nor anything for stretch of other critical fasteners like main studs. Throw me a bone here... what are you typically seeing for stretch on a SBC head bolt? I'd like to work backwards and see what it equates to in clamping load.
ARP also mentions that rod bolts are unique in their clamping loads, for obvious reasons, where as other bolts are not and thus do not require such precision tightening methods.
Back to head stud stretch... how are you going about it? I can't find specs.. so I'd assume that you are checking the stud prior to torquing, then torquing the nut to required spec and remeasuring? Are you using TTA or just a torque wrench? Are you cycling the threads?
Checking torque with an already stretched-to-spec bolt (your ARP rod bolt stretch example) isn't really telling you much. There's an old rule of thumb that suggest a 90/10 relationship for fasteners, where 90% of the force applied is countering friction and 10% is used to stretch the bolt. So it's obvious that the type of lubricant used plays a big part on torque specs as measured with a torque wrench. Cycling the threads applies in the same way. So, unless you duplicate the original procedure to the letter... your results are going to differ. Not that it matters too much cause you're after the end result (the proper stretch).
On the head gasket and retorque... I think it still depends on the gasket. Some don't require it and others do. Has really nothing to do with the method of torquing or how much load you place on the fastener. Some gaskets just loose a little compressed height after a heat cycle or two.
-Mindgame
Last edited by Mindgame; Aug 4, 2004 at 11:32 AM.
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Re: Retorquing Cylinder Heads?
The spects are not in their catalog.You have to get the book from ARP you can also get the spects from Bowman in their spect book.
As stated above I use an electronic dial indictor.You zero the machine on a hand tight stug,then stretch to spect,mains, heads and rods.I can give you values for different grades and sizes if you like.
I wire brush the threads with a bench grinder and check to see if the nut will screw on by hand.If not I run a tap through it with the correct % of thread.Then I pull all bolts to 75% of torque value and back them off.Then pull to streach value.At stretch value I have not found any head gasket that shrinks to loosen the bolt after heat cycling,so I don't worry with retorqueing.That goes for "O" ringed engines and copper gaskets too.
It has been a bunch of years since I got the spect book,so I can't tell you who to talk to at ARP.This method has worked for me a number of year's,and I learned a lot from brand X with 1 less head bolt per cyl and how to keep head gaskets on,with a couple hundred horse of NO added.
As stated above I use an electronic dial indictor.You zero the machine on a hand tight stug,then stretch to spect,mains, heads and rods.I can give you values for different grades and sizes if you like.
I wire brush the threads with a bench grinder and check to see if the nut will screw on by hand.If not I run a tap through it with the correct % of thread.Then I pull all bolts to 75% of torque value and back them off.Then pull to streach value.At stretch value I have not found any head gasket that shrinks to loosen the bolt after heat cycling,so I don't worry with retorqueing.That goes for "O" ringed engines and copper gaskets too.
It has been a bunch of years since I got the spect book,so I can't tell you who to talk to at ARP.This method has worked for me a number of year's,and I learned a lot from brand X with 1 less head bolt per cyl and how to keep head gaskets on,with a couple hundred horse of NO added.
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From: LA (lower Alabama)
Re: Retorquing Cylinder Heads?
MG,
I called ARP to see if I could get you a book of spects.I talked to AL and he said they don't offer those spects anymore.They just use torque values and he agreed that the torque spects are generic but usable.He said they were getting to many questions about stretch and how to do it.He said if you needed stretch spects for an individual bolt kit he could provide them,but not a book that listed all bolt products.I had better put my spect book in a safe place or I won't have one.
I called ARP to see if I could get you a book of spects.I talked to AL and he said they don't offer those spects anymore.They just use torque values and he agreed that the torque spects are generic but usable.He said they were getting to many questions about stretch and how to do it.He said if you needed stretch spects for an individual bolt kit he could provide them,but not a book that listed all bolt products.I had better put my spect book in a safe place or I won't have one.
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From: Kingsport, TN
Re: Retorquing Cylinder Heads?
Originally Posted by Mindgame
On the head gasket and retorque... I think it still depends on the gasket. Some don't require it and others do. Has really nothing to do with the method of torquing or how much load you place on the fastener. Some gaskets just loose a little compressed height after a heat cycle or two.
-Mindgame
-Mindgame
Good info so far guys. Keep up the good work.
Brian
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From: In a house by the bay
Re: Retorquing Cylinder Heads?
Some of the composition gaskets require a retorque. At least that's what GM recommends with some, like this BBC head gasket (10126768 Composition Head Gasket 1965-90)...
http://www.gmgoodwrench.com/gmgoodwr...339§ion=ep
This is from a Victor Reinz engineer on head gaskets... last paragraph is the one dealing with retorque..
Good article. If you're interested in reading the whole thing (rather long), here's the link...
http://engineparts.com/products/gstory.htm
Rol and a few other companies also recommended a retorque with some of their older gasket designs but Rol and others have gone to new types that don't necessarily "require" it. Fel pro has their Permatorque gasket... doesn't require retorque. Many of the MLS gaskets also don't require retorque. They supposedly don't take a "set" after heat cycling. But they also have very specific head/block finishing requirements to seal properly. Copper gaskets don't require retorque either.
Best thing to do is talk to the gasket maker and see what they have to say. They know what's best for their gaskets as they all have their own labs testing them.
Either way, I don't think there is any harm in running back through all the head bolts. I'm not totally sold on the validity of measuring stretch on head studs but I'm not discounting it either. Considering the use of cylinder heads with bolts running through the intake ports like the sb2.2 and how next-to-impossible it would be to get a stretch reading on those studs. I'm under the impression that there are just more important factors like...
·proper # of cycles
·good clean threads (bolt and block)
·adequate hole chamfer
·proper lube-type and application per manufacturer's recommendation
·calibrated torque wrench
·TTA for final setting
-Mindgame
http://www.gmgoodwrench.com/gmgoodwr...339§ion=ep
This is from a Victor Reinz engineer on head gaskets... last paragraph is the one dealing with retorque..
The other issue is the ability to seal combustion, which can be done in numerous ways. One of the methods mentioned briefly was the wire ring approach, a typical low carbon steel wire wrapped with a stainless steel flange balanced to the body gauge. The balance issue implies there will be enough load distributed over the entire gasket to seal all fluids while maintaining a combustion seal. The wire ring technology comes from the heavy-duty industry that seal pressures for diesel engines from 2000 psi on the low side to 4000 psi on the present limit. To accomplish these goals, the components are large and are designed to incorporate the bolt load needed for these high pressures. This is not always the case in performance engines; many components are of stock configuration and many more made of aluminum. The cylinder heads, as I mentioned earlier, are bent over the head gasket, so why use gaskets with wire rings? The use of wire rings can be justified when the firing pressure exceeds 1200 psi. Notice I did not give a compression ratio, because there are many factors that determine the actual firing pressure. The compression ratio, the volume of air, and the moment of ignition are all vital to the formula. A good example of this would be the new use of bottled horsepower; the compression ratio doesn’t change to increase horsepower yet the output when you hit the button is dramatically altered.
When the decision has been made to use the wire ring concept for head gasket, the issue of bending will be helped with the use of a retorque. Whether or not the wire ring has been preflattened the exercise of setting the gasket to the conditions of the particular application help assure a positive seal of combustion and fluids. The operation of a race engine by its nature is designed to push gaskets to the extreme limits, some push harder than others but the effort to make the gasket as a foundation to the system should not be taken lightly
When the decision has been made to use the wire ring concept for head gasket, the issue of bending will be helped with the use of a retorque. Whether or not the wire ring has been preflattened the exercise of setting the gasket to the conditions of the particular application help assure a positive seal of combustion and fluids. The operation of a race engine by its nature is designed to push gaskets to the extreme limits, some push harder than others but the effort to make the gasket as a foundation to the system should not be taken lightly
http://engineparts.com/products/gstory.htm
Rol and a few other companies also recommended a retorque with some of their older gasket designs but Rol and others have gone to new types that don't necessarily "require" it. Fel pro has their Permatorque gasket... doesn't require retorque. Many of the MLS gaskets also don't require retorque. They supposedly don't take a "set" after heat cycling. But they also have very specific head/block finishing requirements to seal properly. Copper gaskets don't require retorque either.
Best thing to do is talk to the gasket maker and see what they have to say. They know what's best for their gaskets as they all have their own labs testing them.
Either way, I don't think there is any harm in running back through all the head bolts. I'm not totally sold on the validity of measuring stretch on head studs but I'm not discounting it either. Considering the use of cylinder heads with bolts running through the intake ports like the sb2.2 and how next-to-impossible it would be to get a stretch reading on those studs. I'm under the impression that there are just more important factors like...
·proper # of cycles
·good clean threads (bolt and block)
·adequate hole chamfer
·proper lube-type and application per manufacturer's recommendation
·calibrated torque wrench
·TTA for final setting
-Mindgame
Last edited by Mindgame; Aug 4, 2004 at 03:00 PM.