The magic IM bolt-loosening phenomenon revealed and a work-around for it...
09-10-2008, 05:47 AM
#1
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The magic IM bolt-loosening phenomenon revealed and a work-around for it...
<center><img src="http://pictureposter.audiworld.com/711/imtorquesequence.jpg"></center><p>
Ok guys while the issue here is very simple the solution is quite complex and likely beyond the means of most.
First the issue:
As I posted last week my M6x1mm (small) IM bolts had mysteriously loosened which I found while chasing what I know to be an IM leak. The bolts that secure the upper/lower manifold halves which have a torque spec per Bentley of 7 ft lbs had inexplicably loosened overnight after the IM was re-installed in the car. After mentioning it here and a LOT of head scratching I gave up trying to understand how/why and got down to trying to solve the bigger issue of an IM leak. Yesterday when test-assembling my lapped and re-sealed IM to a pair of spare of 12V heads I keep around the loosening IM bolts reared their ugly head again... Now it's getting annoying!
So I backed off the M8x1.25mm (larger) IM bolts that attach the assembled IM to the cylinder heads and guess what!?! Yep, the M6x1mm (smaller) upper/lower fasteners were right back at the exact torque they were installed at, ie; 7 ft lbs! And therein lies both the issue and the solution.
When the 5mm bolts are installed to attach the IM upper lower halves they are torqued to 7 ft lbs. Then when installing the IM and bolt it to the cylinder heads we torque those bolts to 15 ft lbs. Well this higher torque compresses the gasket between upper/lower halves further and by narrowing gap between upper/lower halves causes the 5mm bolts to now be loose. Their previous 7 ft lb torque setting now runs from 2-6 ft lbs and is directly related to how close those 5mm/7 ft lb bolts are to the larger M8x1.25mm/15 ft lb bolts. Upper/lower IM fastening bolts that are very close to the larger cylinder head mounting bolts become very loose and those further away from the larger bolts loosen less. But they ALL loosen to a greater/lesser degree! By having my IM installed to spare heads I was also able to confirm this happens to the upper/lower manifold halves that are installed from beneath the IM. And they are the ones MOST affected! You could actually spin the washers underneat their heads "after" they had been torqued to spec and the IM was torqued to the cylinder heads!
Now the solution:
All good torque-sequencing practice will ALWAYS be based on a "center-out" basis. That is to say correct tightening sequences should always be done from the center outwards. Doesnt matter the geometry... The part you're torqueing could be long/narrow, round or square but should always be torqued from the center out and in a criss-cross pattern when dealing with rectangular geometries. Bentley offers no tightening sequence for the IM upper/lower halves or the sequence for IM-to-cylinder head torque sequence. They simply tell you what the bolt torque specs are and leave you to figure it out. Sounds easy right? In our case, FAR from it! In order for us to reassemble, install and torque-to-spec an IM correctly virtually dictates the need for a pair of spare cylinder heads... there's just no way around it!
12V IM correct torque sequencing:
As mentioned above we need a pair of spre heads to do this. I originally thought we might be able to get away with just a single spare head but the dynamic indicates we "must" have 2 to do this correctly and both should have "flat" gasket flanges.
1. Assemble IM upper/lower halves with a new gasket. If using sealant go ahead and apply it making sure all gasket surfaces are meticulously cleaned and prepped. Once gasket is in place drop upper manifold half on to lower manifold half carefully lining up front/rear locating pins and rop into place and install a few front/rear and M6x1mm side screws turned in hand-tight to keep halves from seaparting while you work.
2. Now turn manifold/heads assembly upside-down and install the 4 long IM upper/lower half bolts but apply no Loctite at this time. Torque those 4 bolts to 7 ft lbs in a criss-cross pattern then rotate manifold back to right-side up.
3. Now attach IM to cylinder heads using all 10 M8x1mm bolts for this and and starting from center and working outwards torque to 15 ft lbs (no Loctite). Since heads are not attached to the engine there's no need for "criss-cross" sequencing from one side to the other. Just do one side first starting in the middle and working outwards to the right then middle-to-left. Repeat on both banks. After you've done this, re-torque everything again in exactly the same pattern/sequence as the gasket between IM halves will compress. If time is not an issue doing it a 3rd time after an hour or two is even better as the gasket will compress even more. Or let it sit overnight then re-torque for best results.
4. Now install all M6x1mm IM perimeter bolts and tighten in a "center-out" pattern along both sides to 7 ftlbs using no Loctite. Then do the same thing at front/rear of IM torqueing 2 center bolts first then moving to the outer 2 bolts, again NO Lctite at this point.
4. Once you're convinced that your gasket has compressed all it's going to you can then flip the IM back over exposing the bottom. You'll now find those 4 bolts are looser than you torqued them originally. Now remove them in any sequence and apply Loctite to them and reinstall and re-torque in a criss-cross pattern to 7 ft lbs. You're now done with those 4 bolts.
5. Flip IM back over and removing only one 5mm bolt at a time apply Loctite to it and re-install/torque to 7ft lbs. If you only remove one bolt at a time there's no need for maintaining the "center-out" pattern they were installed in initially without Loctite.
6. Set entire IM/heads assembly aside and allow everything to settle-in for 24 hours.
7. Leave everything assembled as-is until installation into car. Once everything is ready for the IM install only then remove IM from spare heads and install as quickly as possible on to the heads in car and torque to 15ft lbs with NO Loctite. Allow IM-to-head gaskets to compress for 12-24 hours then remove them one at a time and apply Loctite and re-install them and torque to 15ft lbs and in the proper "center-out" sequence.
Pic above shows all the fasteners involved. Legends are as follows:
Red circles are M6x1mm bolts used to secure manifold halves together and are 7ft lb torque spec.
Red circles with red "X" inside are IM underside upper/lower half M6x1mmmm securing bolts and are 7ft lb torque.
Blue circles are IM-to-head M8x1.25mm fastening bolts and are 15ft lb torque.
I know this is complicated as well as I know it'll be only practiced by a handful of people if any. Obviously people have been installing 12V IM's on 12V cars for years without incident. But do you REALLY know if your IM is 100% sealed!?! And there's no doubt if I hadn't suffered a leaky IM last week I wouldn't have done this this week. But I've got a strong gut-level hunch my IM will be TOTALLY 100% sealed this time and I know I'll NEVER do it ANY other way again! It's a H-U-G-E PITA to do it this way but nowhere near as big a pain as doing it twice within a week! And If I can't find the time to do it REALLY right where do I get the time to do it over!?!
Ok guys while the issue here is very simple the solution is quite complex and likely beyond the means of most.
First the issue:
As I posted last week my M6x1mm (small) IM bolts had mysteriously loosened which I found while chasing what I know to be an IM leak. The bolts that secure the upper/lower manifold halves which have a torque spec per Bentley of 7 ft lbs had inexplicably loosened overnight after the IM was re-installed in the car. After mentioning it here and a LOT of head scratching I gave up trying to understand how/why and got down to trying to solve the bigger issue of an IM leak. Yesterday when test-assembling my lapped and re-sealed IM to a pair of spare of 12V heads I keep around the loosening IM bolts reared their ugly head again... Now it's getting annoying!
So I backed off the M8x1.25mm (larger) IM bolts that attach the assembled IM to the cylinder heads and guess what!?! Yep, the M6x1mm (smaller) upper/lower fasteners were right back at the exact torque they were installed at, ie; 7 ft lbs! And therein lies both the issue and the solution.
When the 5mm bolts are installed to attach the IM upper lower halves they are torqued to 7 ft lbs. Then when installing the IM and bolt it to the cylinder heads we torque those bolts to 15 ft lbs. Well this higher torque compresses the gasket between upper/lower halves further and by narrowing gap between upper/lower halves causes the 5mm bolts to now be loose. Their previous 7 ft lb torque setting now runs from 2-6 ft lbs and is directly related to how close those 5mm/7 ft lb bolts are to the larger M8x1.25mm/15 ft lb bolts. Upper/lower IM fastening bolts that are very close to the larger cylinder head mounting bolts become very loose and those further away from the larger bolts loosen less. But they ALL loosen to a greater/lesser degree! By having my IM installed to spare heads I was also able to confirm this happens to the upper/lower manifold halves that are installed from beneath the IM. And they are the ones MOST affected! You could actually spin the washers underneat their heads "after" they had been torqued to spec and the IM was torqued to the cylinder heads!
Now the solution:
All good torque-sequencing practice will ALWAYS be based on a "center-out" basis. That is to say correct tightening sequences should always be done from the center outwards. Doesnt matter the geometry... The part you're torqueing could be long/narrow, round or square but should always be torqued from the center out and in a criss-cross pattern when dealing with rectangular geometries. Bentley offers no tightening sequence for the IM upper/lower halves or the sequence for IM-to-cylinder head torque sequence. They simply tell you what the bolt torque specs are and leave you to figure it out. Sounds easy right? In our case, FAR from it! In order for us to reassemble, install and torque-to-spec an IM correctly virtually dictates the need for a pair of spare cylinder heads... there's just no way around it!
12V IM correct torque sequencing:
As mentioned above we need a pair of spre heads to do this. I originally thought we might be able to get away with just a single spare head but the dynamic indicates we "must" have 2 to do this correctly and both should have "flat" gasket flanges.
1. Assemble IM upper/lower halves with a new gasket. If using sealant go ahead and apply it making sure all gasket surfaces are meticulously cleaned and prepped. Once gasket is in place drop upper manifold half on to lower manifold half carefully lining up front/rear locating pins and rop into place and install a few front/rear and M6x1mm side screws turned in hand-tight to keep halves from seaparting while you work.
2. Now turn manifold/heads assembly upside-down and install the 4 long IM upper/lower half bolts but apply no Loctite at this time. Torque those 4 bolts to 7 ft lbs in a criss-cross pattern then rotate manifold back to right-side up.
3. Now attach IM to cylinder heads using all 10 M8x1mm bolts for this and and starting from center and working outwards torque to 15 ft lbs (no Loctite). Since heads are not attached to the engine there's no need for "criss-cross" sequencing from one side to the other. Just do one side first starting in the middle and working outwards to the right then middle-to-left. Repeat on both banks. After you've done this, re-torque everything again in exactly the same pattern/sequence as the gasket between IM halves will compress. If time is not an issue doing it a 3rd time after an hour or two is even better as the gasket will compress even more. Or let it sit overnight then re-torque for best results.
4. Now install all M6x1mm IM perimeter bolts and tighten in a "center-out" pattern along both sides to 7 ftlbs using no Loctite. Then do the same thing at front/rear of IM torqueing 2 center bolts first then moving to the outer 2 bolts, again NO Lctite at this point.
4. Once you're convinced that your gasket has compressed all it's going to you can then flip the IM back over exposing the bottom. You'll now find those 4 bolts are looser than you torqued them originally. Now remove them in any sequence and apply Loctite to them and reinstall and re-torque in a criss-cross pattern to 7 ft lbs. You're now done with those 4 bolts.
5. Flip IM back over and removing only one 5mm bolt at a time apply Loctite to it and re-install/torque to 7ft lbs. If you only remove one bolt at a time there's no need for maintaining the "center-out" pattern they were installed in initially without Loctite.
6. Set entire IM/heads assembly aside and allow everything to settle-in for 24 hours.
7. Leave everything assembled as-is until installation into car. Once everything is ready for the IM install only then remove IM from spare heads and install as quickly as possible on to the heads in car and torque to 15ft lbs with NO Loctite. Allow IM-to-head gaskets to compress for 12-24 hours then remove them one at a time and apply Loctite and re-install them and torque to 15ft lbs and in the proper "center-out" sequence.
Pic above shows all the fasteners involved. Legends are as follows:
Red circles are M6x1mm bolts used to secure manifold halves together and are 7ft lb torque spec.
Red circles with red "X" inside are IM underside upper/lower half M6x1mmmm securing bolts and are 7ft lb torque.
Blue circles are IM-to-head M8x1.25mm fastening bolts and are 15ft lb torque.
I know this is complicated as well as I know it'll be only practiced by a handful of people if any. Obviously people have been installing 12V IM's on 12V cars for years without incident. But do you REALLY know if your IM is 100% sealed!?! And there's no doubt if I hadn't suffered a leaky IM last week I wouldn't have done this this week. But I've got a strong gut-level hunch my IM will be TOTALLY 100% sealed this time and I know I'll NEVER do it ANY other way again! It's a H-U-G-E PITA to do it this way but nowhere near as big a pain as doing it twice within a week! And If I can't find the time to do it REALLY right where do I get the time to do it over!?!
09-10-2008, 09:48 AM
#3
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So do you think Audi used this torque sequence from the factory...
or could this problem be directly related to the 60% thicker gasket material and liquid sealant you use? In my opinion normal gaskets without sealant <i>might</i> be an easier work around for most people. It's been proven to work in this application for the last 17 years, why reinvent the wheel? I've seen gaskets the thickness of wax paper create a perfectly good seal, so it's not all about the thickness of material, and how much liquid sealant you use that creates a good seal.
09-10-2008, 10:16 AM
#4
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Thread Starter
My leaker was stock/OEM gaskets. I was gonna try my thicker stuff...
as it would definately be a better choice in a "leaking" situation but proved too old/brittle to be trust-worthy.
And your concerns about my "reinventing the wheel" were listed in the original post so your re-mention of it is a little like the "department of redundancy department." As I said in that post; "Obviously people have been installing 12V IM's on 12V cars for years without incident. But do you REALLY know if your IM is 100% sealed!?!"
These are my findings. No one is soliciting imitation at gun point. You're all free to do as you see fit. This is the way I'm going any/every time I remove the IM from now on. You are free to continue doing it the way you always have and I promise not to ask you any more-rhetorical-than-real questions about it.
This is why there's chocolate/vanilla, Chevys & Fords... a lid for every pot and a butt for every seat. Viva le difference!
And your concerns about my "reinventing the wheel" were listed in the original post so your re-mention of it is a little like the "department of redundancy department." As I said in that post; "Obviously people have been installing 12V IM's on 12V cars for years without incident. But do you REALLY know if your IM is 100% sealed!?!"
These are my findings. No one is soliciting imitation at gun point. You're all free to do as you see fit. This is the way I'm going any/every time I remove the IM from now on. You are free to continue doing it the way you always have and I promise not to ask you any more-rhetorical-than-real questions about it.
This is why there's chocolate/vanilla, Chevys & Fords... a lid for every pot and a butt for every seat. Viva le difference!
09-10-2008, 02:00 PM
#6
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Thread Starter
As specifically stated in the post above under both the "solution" and "12V torque sequencing"...
sections; I cannot come up with a work-around for not having a spare set of heads. Work-around concepts graciously accepted. Nothing else will keep the manifold as "dimensionally stable/locked-in" as the identical position for this that the manifold is in during use. I thought initially one might be able to do it on the car but the step involving the bottom 4 mounting screws doesnt permit car heads to be used simply because you cannot access those 4 bolts with the manifold bolted to the car's heads.
"In order for us to reassemble, install and torque-to-spec an IM correctly, virtually dictates the need for a pair of spare cylinder heads... there's just no way around it! Tho as I and another have stated, you have options in how you assemble and install your own IM and admittedly this may be a little too "cutting edge" for some and/or too logistically difficult to accomplish for others.
12V IM correct torque sequencing:
As mentioned above we need a pair of spare heads to do this. I originally thought we might be able to get away with just a single spare head but the dynamic indicates we "must" have 2 to do this correctly and both should have "flat" gasket flanges."
I intentionally refrained from listing a numerical sequence opting instead for a "center-out" explanation description. Basically as below:
left side: center-out
Right side: center-out
Front: center-out
rear: center-out
Numerical sequencing makes it look as if there's only one start-stop point when in point of fact you could start the sequence on left side or right side... long as you sequence in "center-out" order. If it helps to have a numerical sequence please feel free to cut/paste a copy of the pic I posted and insert numbers for your own use. Also it'll ALWAYS be easier to remember "center-out" than an actual numerical sequence pattern for 25 fasteners without a cheat-sheet!
"In order for us to reassemble, install and torque-to-spec an IM correctly, virtually dictates the need for a pair of spare cylinder heads... there's just no way around it! Tho as I and another have stated, you have options in how you assemble and install your own IM and admittedly this may be a little too "cutting edge" for some and/or too logistically difficult to accomplish for others.
12V IM correct torque sequencing:
As mentioned above we need a pair of spare heads to do this. I originally thought we might be able to get away with just a single spare head but the dynamic indicates we "must" have 2 to do this correctly and both should have "flat" gasket flanges."
I intentionally refrained from listing a numerical sequence opting instead for a "center-out" explanation description. Basically as below:
left side: center-out
Right side: center-out
Front: center-out
rear: center-out
Numerical sequencing makes it look as if there's only one start-stop point when in point of fact you could start the sequence on left side or right side... long as you sequence in "center-out" order. If it helps to have a numerical sequence please feel free to cut/paste a copy of the pic I posted and insert numbers for your own use. Also it'll ALWAYS be easier to remember "center-out" than an actual numerical sequence pattern for 25 fasteners without a cheat-sheet!
09-10-2008, 02:14 PM
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The question wasn't only about the thicker gasket, but also the liquid sealant
Mance, I have no concern for you personally reinventing the wheel. I clearly said it was my <i>opinion</i> that dry OEM gaskets <i>might</i> work better for <i>most</i> people... Unless you're trying to say your situation is the same as everyone else on this forum, that should have been pretty obvious :rolls eyes:
For everyone else, my theory is that the liquid sealant isn't compressed fully at 7ft lbs. When you torque the last 10 bolts to 15ft lbs it gets compressed a little bit more, making the other bolts appear to loosen. A standard dry paper gasket is compressed enough at 7ft lbs. When the last 10 bolts are torqued to 15ft lbs it doesn't compress anymore (or enough) and make it look like the other bolts loosen. Since it has been made clear that no one will get shot for trying something else, I suggest a dry paper gasket like it came with from the factory.
The first question I'm going to ask the next person who has this problem is if they used a liquid sealant.
For everyone else, my theory is that the liquid sealant isn't compressed fully at 7ft lbs. When you torque the last 10 bolts to 15ft lbs it gets compressed a little bit more, making the other bolts appear to loosen. A standard dry paper gasket is compressed enough at 7ft lbs. When the last 10 bolts are torqued to 15ft lbs it doesn't compress anymore (or enough) and make it look like the other bolts loosen. Since it has been made clear that no one will get shot for trying something else, I suggest a dry paper gasket like it came with from the factory.
The first question I'm going to ask the next person who has this problem is if they used a liquid sealant.
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09-10-2008, 03:09 PM
#8
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the thing to remember about liquid sealants is while they "might" not be necessary they don't...
harm anything. Over 99% of any/all sealant is compressed out and away from the gasket it was applied to when torqued. The film membrane that remains is in the VERY thn +/- "half of one ten thousandths" of an inch thickness between the mating and gasket surfaces. A far FAR cry from the kind of thickness that would cause a fastener to lose 85% of it's torque setting... or even 1% of it! On brand new "virgin" cast/CNC'd IM's like Pierburg assembled and sold to Audi there's likely .0000" indicated warpage between the mated upper/lower halves. Same with brand spanking new oil pans, tranny pans and FD covers etc. Over the years and decades thru heat cyling, expansion/contraction etc things have a tendency to warp/distort. The 12V valley pan covers are prime examples. Virtually never see more than 200*F yet literally NEVER can one be removed that isn't warped and even if re-installed with a new gasket and seal back up 100%. Without lapping flat and the further use of a quality sealant it's virtually guaranteed to leak again immediately! And when lapped using a marker you can easily see why it leaks. Only the bolt areas are sealing while the spans between the bolts are not even touching the engine block's deck or the gasket under it! Sealant is a "form-fitting" insurance policy that while maybe unnecessary is a good way to hedge ALL your gasket bets. It allows expansion/contraction while remaining adhered to 2 surfaces that are less than ideal/perfect as well as sealing the gasket surface material itself whereas the dry paper simply lies there during expansion/contraction AND warpage and allows leaks both over, under and "thru" via absorption, permeation and saturation of it's material composition. Sealants go a long way preventing that altogether and/or dramatically extending a gaskets material life. But the biggest truth in all this is that liquid sealants simply do not harm/hurt anything especially when working with "seasoned" mating surfaces that are no longer pristinely flat and true to their mated halves. No one would prefer sealants as they're messy during application and when it comes to cleanup replacing a gasket. But fortunately that occurence only comes around once every 100+k miles or so.
After now having tested 3 IM's for flatness and still not finding one that is, it is my belief they're ALL warped today. I don't know much but I do know there's not an OEM gasket on the planet, applied dry that's going to seal one of them as well as they "can" be sealed..
And the biggest nagging question to both myself and anyone/everyone else here would be; How exactly do "we" know "empirically" we have a totally sealed IM since the symptoms when less than a 20% leakage are so similar to other ails we'd expect from a 100k+ miles engine!?! Seriously, how do we KNOW our IM is not leaking? What are your, mine and everyone's here static idle vacuum measuremants in inches/mercury when car is at normal operating temperature?
I think when we start seeing some of those numbers we'll be well on our way to better understanding the need and use of sealants and ideally a better performing, more efficient engine in the process.
After now having tested 3 IM's for flatness and still not finding one that is, it is my belief they're ALL warped today. I don't know much but I do know there's not an OEM gasket on the planet, applied dry that's going to seal one of them as well as they "can" be sealed..
And the biggest nagging question to both myself and anyone/everyone else here would be; How exactly do "we" know "empirically" we have a totally sealed IM since the symptoms when less than a 20% leakage are so similar to other ails we'd expect from a 100k+ miles engine!?! Seriously, how do we KNOW our IM is not leaking? What are your, mine and everyone's here static idle vacuum measuremants in inches/mercury when car is at normal operating temperature?
I think when we start seeing some of those numbers we'll be well on our way to better understanding the need and use of sealants and ideally a better performing, more efficient engine in the process.
09-10-2008, 04:35 PM
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what if you "sat" on the IM to do the IM half bolts...
for example, say you did your IM half bolts center out to 7lbs and then applied pressure (stack of a lot of books for ex) on top of the IM to simulate being sandwiched down with the heads and the IM head bolts. And then re-tighten the IM half bolts. Just trying to do a work around for the bottom four bolts, other wise its all very doable with out a separate pair of heads...just those four