Torquing Heads
08-23-2011, 07:01 PM
#16
Drifting
The great thing about the 928 heads is you have line of sight on every head bolt, I've since discovered that on other marques that is not always the case - what a nightmare!
08-23-2011, 09:22 PM
#17
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So.....
Since you bought a nice tool...I'll give you some additonal help, that I wasn't going to bother with, before.
That feeling that you think is the "head gasket" compressing is, in reality, one of the head washers spinning on the head....which is strictly forbidden, by Porsche. Whenever the torque required to turn decreases suddenly, this is what happened.
Whenever this happens, to me, I start over.
The surface between the washer and the head must be completely dry. The head nuts need to be lubricated between them and the washer. I use a special high pressure never sieze. If the washers continue to spin, you can remove them and "sand" an aggresive "cross hatch" onto the face that touches the head. I use 220 on a very flat surface.
I actually do all the washers, before I start....I got really tired of this happening.
Since you bought a nice tool...I'll give you some additonal help, that I wasn't going to bother with, before.
That feeling that you think is the "head gasket" compressing is, in reality, one of the head washers spinning on the head....which is strictly forbidden, by Porsche. Whenever the torque required to turn decreases suddenly, this is what happened.
Whenever this happens, to me, I start over.
The surface between the washer and the head must be completely dry. The head nuts need to be lubricated between them and the washer. I use a special high pressure never sieze. If the washers continue to spin, you can remove them and "sand" an aggresive "cross hatch" onto the face that touches the head. I use 220 on a very flat surface.
I actually do all the washers, before I start....I got really tired of this happening.
08-23-2011, 09:27 PM
#18
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With your experience it probably does take only an hour or so, but for most of us it takes a long time to torque a pair of heads, during which it's very useful to have someone else protect from distractions and double check the sequence.
The great thing about the 928 heads is you have line of sight on every head bolt, I've since discovered that on other marques that is not always the case - what a nightmare!
The great thing about the 928 heads is you have line of sight on every head bolt, I've since discovered that on other marques that is not always the case - what a nightmare!
I am very **** about doing this, so far longer than a hour, and my guess is that it takes me longer to do them than most here.
08-23-2011, 09:53 PM
#19
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I can't express enough how much I appreciate the comments from Greg and Greg and others. Let me share what I as a newbie learned from this.
1) You can't overestimate the value of a GOOD torque wrench. This SNAP ON wrench makes getting the angle so much easier. I thought the old school gauge was good enough. Nothing further from the truth.
You can always resell a high quality wrench on eBay and recover your investment. Then again, it is so cool I can't understand why you would now that I bought it.
2) You can't watch the washers and hold them and torque at the same time. Pick two of the three. I was given advice to hold them in place with another person using a long awl or something. Can't do that alone
3) You think your engine stand is stable, until you have to crank down on those head bolts, then it is a noodle. I have an engine stand designed for big block chebbies. It wiggles under the torque load.
4) Listen to what someone tells you, especially if they tell you in person and do this for a living.
5) Don't try to torque with the little aluminum cam pins in, you will pinch one between your fingers and the head and bend it necessitating an overnight shipment that costs more than the part.
6) There is a very good reason these guys charge what they charge to build an engine or repair one. The knowledge I have gained from them is valuable. There are trade secrets they will never reveal and that's what you pay them for. They had to pay for them in years and years and years of doing this.
7) Finally, don't be afraid to try. The guy who built your engine initially didn't know how to do it and learned and so can you.
1) You can't overestimate the value of a GOOD torque wrench. This SNAP ON wrench makes getting the angle so much easier. I thought the old school gauge was good enough. Nothing further from the truth.
You can always resell a high quality wrench on eBay and recover your investment. Then again, it is so cool I can't understand why you would now that I bought it.
2) You can't watch the washers and hold them and torque at the same time. Pick two of the three. I was given advice to hold them in place with another person using a long awl or something. Can't do that alone
3) You think your engine stand is stable, until you have to crank down on those head bolts, then it is a noodle. I have an engine stand designed for big block chebbies. It wiggles under the torque load.
4) Listen to what someone tells you, especially if they tell you in person and do this for a living.
5) Don't try to torque with the little aluminum cam pins in, you will pinch one between your fingers and the head and bend it necessitating an overnight shipment that costs more than the part.
6) There is a very good reason these guys charge what they charge to build an engine or repair one. The knowledge I have gained from them is valuable. There are trade secrets they will never reveal and that's what you pay them for. They had to pay for them in years and years and years of doing this.
7) Finally, don't be afraid to try. The guy who built your engine initially didn't know how to do it and learned and so can you.
08-23-2011, 11:13 PM
#20
Former Sponsor
No, takes me far longer than a hour to do a set of 928 heads, and it takes two of us, one to help hold the engine stand and look at the washers to see if they turn, and one run the torque wrench.
I am very **** about doing this, so far longer than a hour, and my guess is that it takes me longer to do them than most here.
I am very **** about doing this, so far longer than a hour, and my guess is that it takes me longer to do them than most here.
I mark all the head washers with a paint pen line and put another line on the head. This makes it really easy to see if they spin.
I'm guessing that 95% of the engines that get assembled, at home, have washers that spin.....maybe more like 99%. If you don't do anything to the washers, but just re-install them, it's almost guaranteed that one or more will spin. If you "feel" a sudden reduction in torque needed to tighten the nuts, the washer just spun.
Less effort=less torque on the fastener.
That's why Greg N. and I "start over".
08-23-2011, 11:15 PM
#21
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I love paint pins that I buy at the local "craft" store. I use them to mark all my hardware. On a chassis, I mark each bolt that I torque with a paint line, when I torque it. That's left over from racing....
I mark all the head washers with a paint pen line and put another line on the head. This makes it really easy to see if they spin.
I'm guessing that 95% of the engines that get assembled, at home, have washers that spin.....maybe more like 99%. If you don't do anything to the washers, but just re-install them, it's almost guaranteed that one or more will spin. If you "feel" a sudden reduction in torque needed to tighten the nuts, the washer just spun.
Less effort=less torque on the fastener.
That's why Greg N. , and I "start over".
I mark all the head washers with a paint pen line and put another line on the head. This makes it really easy to see if they spin.
I'm guessing that 95% of the engines that get assembled, at home, have washers that spin.....maybe more like 99%. If you don't do anything to the washers, but just re-install them, it's almost guaranteed that one or more will spin. If you "feel" a sudden reduction in torque needed to tighten the nuts, the washer just spun.
Less effort=less torque on the fastener.
That's why Greg N. , and I "start over".
08-24-2011, 02:42 AM
#22
Former Sponsor
The only thing I would change is to have the battery cover, at the end of the handle, attach in a different manner, so that it doesn't come loose when you are pulling on the wrench. (The pulling with your hand loosens the cap....naturally.)
You will experience this, if you use it enough.....but it is still a great tool!
08-24-2011, 06:32 AM
#23
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I love paint pins that I buy at the local "craft" store. I use them to mark all my hardware. On a chassis, I mark each bolt that I torque with a paint line, when I torque it. That's left over from racing....
I mark all the head washers with a paint pen line and put another line on the head. This makes it really easy to see if they spin.
I'm guessing that 95% of the engines that get assembled, at home, have washers that spin.....maybe more like 99%. If you don't do anything to the washers, but just re-install them, it's almost guaranteed that one or more will spin. If you "feel" a sudden reduction in torque needed to tighten the nuts, the washer just spun.
Less effort=less torque on the fastener.
That's why Greg N. and I "start over".
I mark all the head washers with a paint pen line and put another line on the head. This makes it really easy to see if they spin.
I'm guessing that 95% of the engines that get assembled, at home, have washers that spin.....maybe more like 99%. If you don't do anything to the washers, but just re-install them, it's almost guaranteed that one or more will spin. If you "feel" a sudden reduction in torque needed to tighten the nuts, the washer just spun.
Less effort=less torque on the fastener.
That's why Greg N. and I "start over".
Torquing by ftlbs I understand completely. The torque spec assumes that the frictional losses are between the bolt head and washer (and also between the fastener threads into the block.) This results in a reduced torque actually applied to the shank of the fastener and with that less pre-compression than a no friction scenario would give. NB Frictional losses can reduce the precompression applied to the parts being clamped by as much as 50% so it's significant. Should the washer spin say because some fool put oil underneath it the reduced losses could result in the fastener being overstressed and going into it's plastic phase - not good or worse stripping the threads in the block.
However when you torque by degrees, to my mind the loss under the head of the bolt is not relevant. When you turn the head of the bolt through 90 degrees you've turned it through 90 degrees - more or less friction under the head makes it harder or easier to turn through 90 but it doesn't affect the rotation imparted to the top of the shank of the fastener and thus the compression of the parts being clamped.
So what am I missing ?
08-24-2011, 06:36 AM
#24
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This is a very valuable and informative thread to me.
Thanks to all of you in what you've shared and asked so far.
I hope this rebuild turns out really well and it probably will!
(interested very much in answer to Jon's question, too.)
Thanks to all of you in what you've shared and asked so far.
I hope this rebuild turns out really well and it probably will!
(interested very much in answer to Jon's question, too.)
08-24-2011, 10:15 AM
#25
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Isn't that a really great torque wrench? I've got 3 of them....in all of the different sizes.
The only thing I would change is to have the battery cover, at the end of the handle, attach in a different manner, so that it doesn't come loose when you are pulling on the wrench. (The pulling with your hand loosens the cap....naturally.)
You will experience this, if you use it enough.....but it is still a great tool!
The only thing I would change is to have the battery cover, at the end of the handle, attach in a different manner, so that it doesn't come loose when you are pulling on the wrench. (The pulling with your hand loosens the cap....naturally.)
You will experience this, if you use it enough.....but it is still a great tool!
The new ones like Jeff bought seem to be better than the old ones.
I bet between us we have enough money in different torque wrenches to buy a really nice 928.
My latest was a detachable head Snap-On in 3/4 that goes to 600 FT/LBS, to go with the 400 FT/LBS one.
I am trying to get a full set of the dial type now, about half way there.
Greg Brown told me a story about a guy that cut some trees in his yard, dude had a chain say and a couple of other little things and charged more than Greg did per hour.
We also use the paint pens and magic markers, a different color for each mechanic.
08-24-2011, 10:18 AM
#26
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the washer will "Seat or Wear in" if it turns, a thousandth or two can make a huge difference in how much compression the gasket sees.
I'm having a problem getting my head around the need to stop the washer spinning when the fastener is being torqued by angle.
Torquing by ftlbs I understand completely. The torque spec assumes that the frictional losses are between the bolt head and washer (and also between the fastener threads into the block.) This results in a reduced torque actually applied to the shank of the fastener and with that less pre-compression than a no friction scenario would give. NB Frictional losses can reduce the precompression applied to the parts being clamped by as much as 50% so it's significant. Should the washer spin say because some fool put oil underneath it the reduced losses could result in the fastener being overstressed and going into it's plastic phase - not good or worse stripping the threads in the block.
However when you torque by degrees, to my mind the loss under the head of the bolt is not relevant. When you turn the head of the bolt through 90 degrees you've turned it through 90 degrees - more or less friction under the head makes it harder or easier to turn through 90 but it doesn't affect the rotation imparted to the top of the shank of the fastener and thus the compression of the parts being clamped.
So what am I missing ?
Torquing by ftlbs I understand completely. The torque spec assumes that the frictional losses are between the bolt head and washer (and also between the fastener threads into the block.) This results in a reduced torque actually applied to the shank of the fastener and with that less pre-compression than a no friction scenario would give. NB Frictional losses can reduce the precompression applied to the parts being clamped by as much as 50% so it's significant. Should the washer spin say because some fool put oil underneath it the reduced losses could result in the fastener being overstressed and going into it's plastic phase - not good or worse stripping the threads in the block.
However when you torque by degrees, to my mind the loss under the head of the bolt is not relevant. When you turn the head of the bolt through 90 degrees you've turned it through 90 degrees - more or less friction under the head makes it harder or easier to turn through 90 but it doesn't affect the rotation imparted to the top of the shank of the fastener and thus the compression of the parts being clamped.
So what am I missing ?
08-24-2011, 03:19 PM
#27
Former Sponsor
I'm having a problem getting my head around the need to stop the washer spinning when the fastener is being torqued by angle.
Torquing by ftlbs I understand completely. The torque spec assumes that the frictional losses are between the bolt head and washer (and also between the fastener threads into the block.) This results in a reduced torque actually applied to the shank of the fastener and with that less pre-compression than a no friction scenario would give. NB Frictional losses can reduce the precompression applied to the parts being clamped by as much as 50% so it's significant. Should the washer spin say because some fool put oil underneath it the reduced losses could result in the fastener being overstressed and going into it's plastic phase - not good or worse stripping the threads in the block.
However when you torque by degrees, to my mind the loss under the head of the bolt is not relevant. When you turn the head of the bolt through 90 degrees you've turned it through 90 degrees - more or less friction under the head makes it harder or easier to turn through 90 but it doesn't affect the rotation imparted to the top of the shank of the fastener and thus the compression of the parts being clamped.
So what am I missing ?
Torquing by ftlbs I understand completely. The torque spec assumes that the frictional losses are between the bolt head and washer (and also between the fastener threads into the block.) This results in a reduced torque actually applied to the shank of the fastener and with that less pre-compression than a no friction scenario would give. NB Frictional losses can reduce the precompression applied to the parts being clamped by as much as 50% so it's significant. Should the washer spin say because some fool put oil underneath it the reduced losses could result in the fastener being overstressed and going into it's plastic phase - not good or worse stripping the threads in the block.
However when you torque by degrees, to my mind the loss under the head of the bolt is not relevant. When you turn the head of the bolt through 90 degrees you've turned it through 90 degrees - more or less friction under the head makes it harder or easier to turn through 90 but it doesn't affect the rotation imparted to the top of the shank of the fastener and thus the compression of the parts being clamped.
So what am I missing ?
Initially, I thought that this probably didn't matter, when torquing at an angle, and they simply "forgot" that this wasn't important any longer.
However, once I figured out that they were "stretching" the studs/bolts and this stretch was partially responsible for keeping the head gaskets "clamped" to the engine, it made more sense. Obviously, if the effort required to turn the hardware goes way down, when the washer slips, the amount of torque on the nut just went down. If the torque went down, so did the amount of stretch on the stud/bolt went down also. It also makes that one stud/bolt have a different amount of stretch, in the end.
I've been messing with keeping heads on, for most of my life. I came from the 911 racing world, so I've seen/used a huge variety of different design head studs, over the years. I also have built a large amount of 951 engines, for high performance use. Air cooled engines (especially turbo engines) have a terrible time keeping the heads tight. 951 engines are all waiting for the conditions that cause a head gasket to fail...they always do...it's just a matter of time.
What I've learned, over the years, is that the people at Porsche aren't stupid....they might have "issues" with a "current" design of hardware, but they know the problems and they are working on a solution, if they do have a problem. I also learned that consistant stretching of the hardware is very critical....actually way more critical than the "torque number".
Even pressure, properly stretched, is the best senario one could ever imagine. I try to make sure that this happens as perfectly as I can make it happen.
08-24-2011, 03:44 PM
#28
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What a great thread!!!!
08-24-2011, 06:24 PM
#29
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Obviously, if the effort required to turn the hardware goes way down, when the washer slips, the amount of torque on the nut just went down. If the torque went down, so did the amount of stretch on the stud/bolt went down also. It also makes that one stud/bolt have a different amount of stretch, in the end.
08-24-2011, 09:56 PM
#30
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Not trying to nitpick, but I still don't get this. If the torque went down because of the washer spinning, but the bolt is turned to the required angle, it just means it was easier to turn the bolt because of less "washer friction" on the bolt head. The bolt is still turned to the desired angle resulting in the desired clamping force. Maybe I didn't understand your explanation though.
I thought about this, for a long time, wondering why Porsche "left" this part of the instruction in the "new" torque proceedure (angle torque.)
Initially, I thought that this probably didn't matter, when torquing at an angle, and they simply "forgot" that this wasn't important any longer.
However, once I figured out that they were "stretching" the studs/bolts and this stretch was partially responsible for keeping the head gaskets "clamped" to the engine, it made more sense. Obviously, if the effort required to turn the hardware goes way down, when the washer slips, the amount of torque on the nut just went down. If the torque went down, so did the amount of stretch on the stud/bolt went down also. It also makes that one stud/bolt have a different amount of stretch, in the end.
I've been messing with keeping heads on, for most of my life. I came from the 911 racing world, so I've seen/used a huge variety of different design head studs, over the years. I also have built a large amount of 951 engines, for high performance use. Air cooled engines (especially turbo engines) have a terrible time keeping the heads tight. 951 engines are all waiting for the conditions that cause a head gasket to fail...they always do...it's just a matter of time.
What I've learned, over the years, is that the people at Porsche aren't stupid....they might have "issues" with a "current" design of hardware, but they know the problems and they are working on a solution, if they do have a problem. I also learned that consistant stretching of the hardware is very critical....actually way more critical than the "torque number".
Even pressure, properly stretched, is the best senario one could ever imagine. I try to make sure that this happens as perfectly as I can make it happen.
Initially, I thought that this probably didn't matter, when torquing at an angle, and they simply "forgot" that this wasn't important any longer.
However, once I figured out that they were "stretching" the studs/bolts and this stretch was partially responsible for keeping the head gaskets "clamped" to the engine, it made more sense. Obviously, if the effort required to turn the hardware goes way down, when the washer slips, the amount of torque on the nut just went down. If the torque went down, so did the amount of stretch on the stud/bolt went down also. It also makes that one stud/bolt have a different amount of stretch, in the end.
I've been messing with keeping heads on, for most of my life. I came from the 911 racing world, so I've seen/used a huge variety of different design head studs, over the years. I also have built a large amount of 951 engines, for high performance use. Air cooled engines (especially turbo engines) have a terrible time keeping the heads tight. 951 engines are all waiting for the conditions that cause a head gasket to fail...they always do...it's just a matter of time.
What I've learned, over the years, is that the people at Porsche aren't stupid....they might have "issues" with a "current" design of hardware, but they know the problems and they are working on a solution, if they do have a problem. I also learned that consistant stretching of the hardware is very critical....actually way more critical than the "torque number".
Even pressure, properly stretched, is the best senario one could ever imagine. I try to make sure that this happens as perfectly as I can make it happen.
