The magic IM bolt-loosening phenomenon revealed and a work-around for it...
09-10-2008, 08:41 PM
#25
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Isn't part of the problem that the bolts have limited space for head size? more inside:
The allen head doesn't have as much torque strength as your typical hex head bolt. The design of the intake manifold yields the necessity for allen heads and therefore lies the problem of not holding the torque value.
As quoted: "but there is no free lunch and, for many of us, particulary for the racer, they also have three disadvantages: first they have very small heads. If they are to be loaded in tension, the limited bearing area under will prevent tightening the bolt sufficienty to take full advantage of the strength of the alloy-unless, of course, a hardened washer is inserted under the bolt head."
So a simpler solution to your setup for the guys who want it easier is: Nordlocks or Belville washers? Ironic don't u think?
Right?
Why not?
As quoted: "but there is no free lunch and, for many of us, particulary for the racer, they also have three disadvantages: first they have very small heads. If they are to be loaded in tension, the limited bearing area under will prevent tightening the bolt sufficienty to take full advantage of the strength of the alloy-unless, of course, a hardened washer is inserted under the bolt head."
So a simpler solution to your setup for the guys who want it easier is: Nordlocks or Belville washers? Ironic don't u think?
Right?
Why not?
09-11-2008, 05:56 AM
#26
AudiWorld Super User
Thread Starter
Neither Nords nor Uni-Torques w/studs would have any affect at all. This is NOT about...
bolts loosening. However, the Belleville's could be just the ticket! I hadn't considered them but in the right diameter, thickness and load rating they could certainly work for the 4 lower bolts that are causing all the grief and work doing this right. Due to the small size I doubt the proper load could could be achieved with only 1 washer but a parallel stack of 2, 3 or 4 could likely work but we'd have to be careful here as anything we do with bellevilles will definately require a REALLY hard (Rockwell C60+ hardness) flat washer both under the allen cap screw head as well as on the IM's bolt seat. There's not much clearance between those bolt heads and the valley pan cover plate. But I'm sure there's +/- 200 thou, maybe more, I'll have to check. Great idea! Sheesh and I built air rifle pressure regulators using Bellevilles for YEARS and NEVER even thought of them... I must be losing it!! This would certainly make IM assembly a sub-1 hour affair without any of the hassles with what I mentioned above.
This whole dilemma is related to one set of bolts being torqued to 7ft lbs then another very nearby set of larger bolts being torqued to 15ft lbs. The bolts don't loosen at all. You can index/reference them with a marker and see that they aren't moving. What's actually happening is the manifold outer perimeter tops/bottoms are assembled with 7ft lb torque settings. Then when the manifold is mounted to the heads the larger bolts, located very close to the smaller ones are then torqued to 15ft lbs. This higher torque/larger bolt compresses the manifold upper/lower halves closer together then the 7ft lb bolts can and thereby relieves the torque on those smaller bolts.
If it weren't for the 4 bolts "under" the IM we could just re-torque the smaller top IM perimeter bolts back to 7ft lbs after installing and torqueing the IM to the heads and call it a day. But now we have those four 7ft lb bolts underneath that also lost their torque when we installed the IM to the heads with 15ft lb bolts. If you could get access to those bolts you'd see when we torqued the IM to the head those 4 bottom bolts lost their torque setting so badly that if you could get access to them you'd see you can now spin their washers by hand. Then when we remove the IM from heads the center section of the IM halves separate once again which gives the false impression that the 4 lower IM bolts have been tight all along. Only way I can know this is by installing an IM to a spare set of heads and when when everything is torqued to spec turn that assembly bottom-side up and re-check torque on those lower 4 bolts. No bolt, stud, washer or threadlocker will prevent prevent the torque from being relieved on 7ft lb fasteners when 15ft lb fasteners are in some cases less than an inch away.
Now having a gap between the upper/lower manifold haves in the center of the IM doesn't necessarily mean an intake leak, nor does it really hurt anything. But what it does do is cause the manifold to warp into that position over time like the manifold "lapping patterns I've shown pics of thru-out this thread. And that happens on manifolds that have been thru the IM Workshop as well as IM's that have NEVER been separated before and have stock gaskets with no sealants that were assembled by Pierburg before being sold to Audi for installation. This further bears out that none of this is related to thicker gasket mayterial or sealants being used. This is purely related to age, mileage, heat cycling and those 4 "un-torqued" bolts in the bottom of the IM. All IMs of the era seem to have "high" center sections with lower outside perimeters as borne out by pics of separated IM's of both genres. That could only happen due to one very specific reason, ie; the 4 bottom center 5mm 7ft lb fasteners have had their 7ft lb torque relieved when the IM was installed on the heads and drive that way at less than specified torque ALL these years since day one!
This whole dilemma is related to one set of bolts being torqued to 7ft lbs then another very nearby set of larger bolts being torqued to 15ft lbs. The bolts don't loosen at all. You can index/reference them with a marker and see that they aren't moving. What's actually happening is the manifold outer perimeter tops/bottoms are assembled with 7ft lb torque settings. Then when the manifold is mounted to the heads the larger bolts, located very close to the smaller ones are then torqued to 15ft lbs. This higher torque/larger bolt compresses the manifold upper/lower halves closer together then the 7ft lb bolts can and thereby relieves the torque on those smaller bolts.
If it weren't for the 4 bolts "under" the IM we could just re-torque the smaller top IM perimeter bolts back to 7ft lbs after installing and torqueing the IM to the heads and call it a day. But now we have those four 7ft lb bolts underneath that also lost their torque when we installed the IM to the heads with 15ft lb bolts. If you could get access to those bolts you'd see when we torqued the IM to the head those 4 bottom bolts lost their torque setting so badly that if you could get access to them you'd see you can now spin their washers by hand. Then when we remove the IM from heads the center section of the IM halves separate once again which gives the false impression that the 4 lower IM bolts have been tight all along. Only way I can know this is by installing an IM to a spare set of heads and when when everything is torqued to spec turn that assembly bottom-side up and re-check torque on those lower 4 bolts. No bolt, stud, washer or threadlocker will prevent prevent the torque from being relieved on 7ft lb fasteners when 15ft lb fasteners are in some cases less than an inch away.
Now having a gap between the upper/lower manifold haves in the center of the IM doesn't necessarily mean an intake leak, nor does it really hurt anything. But what it does do is cause the manifold to warp into that position over time like the manifold "lapping patterns I've shown pics of thru-out this thread. And that happens on manifolds that have been thru the IM Workshop as well as IM's that have NEVER been separated before and have stock gaskets with no sealants that were assembled by Pierburg before being sold to Audi for installation. This further bears out that none of this is related to thicker gasket mayterial or sealants being used. This is purely related to age, mileage, heat cycling and those 4 "un-torqued" bolts in the bottom of the IM. All IMs of the era seem to have "high" center sections with lower outside perimeters as borne out by pics of separated IM's of both genres. That could only happen due to one very specific reason, ie; the 4 bottom center 5mm 7ft lb fasteners have had their 7ft lb torque relieved when the IM was installed on the heads and drive that way at less than specified torque ALL these years since day one!
09-11-2008, 07:43 AM
#27
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are Bellevilles some sort of spring loaded bolt or something?
<ul><li><a href="http://www.keybellevilles.com/largebelleville.html">http://www.keybellevilles.com/largebelleville.html</a</li></ul>
09-11-2008, 11:29 AM
#29
AudiWorld Senior Member
Mance, since there may not be a critical order to -dis-assembling- the I/M...
...that might encourage further warping, could you measure the -resultant- torque remaining on all of the individual small dia. bolts, both after the larger ones have been removed; and after using your complete "spare heads" method?
This would require that you take it apart yet again, but it might also provide us with target numbers which might approach the effectiveness of the complete procedure, i.e. a short-cut?
Since only three(?) of the big ten bolts actually clamp the upper and lower halves together, could we -mock- install and torque just these three, possibly with some (simple?) "torque plates" if required (without actually bolting the I/M to the heads) to aid in clamping the I/M together?
I'm thinking three wedge shaped washers to fit those three locations. These would allow the I/M to be set aside, totally clamped for everything to settle.
Armed with the above, could we then torque from the centre out on each of the four sides, as I believe your suggesting, and thus assemble the two halves more effectively than we otherwise would have been able to?
This would require that you take it apart yet again, but it might also provide us with target numbers which might approach the effectiveness of the complete procedure, i.e. a short-cut?
Since only three(?) of the big ten bolts actually clamp the upper and lower halves together, could we -mock- install and torque just these three, possibly with some (simple?) "torque plates" if required (without actually bolting the I/M to the heads) to aid in clamping the I/M together?
I'm thinking three wedge shaped washers to fit those three locations. These would allow the I/M to be set aside, totally clamped for everything to settle.
Armed with the above, could we then torque from the centre out on each of the four sides, as I believe your suggesting, and thus assemble the two halves more effectively than we otherwise would have been able to?