Back off 1/4 or no on head retorque

[49er]

True. Some torque figures are dry but most are wet/lubed. I believe that all the GS torque figures are lubed values. And yes, you should always back off the tension on each nut usually between 1/4 to 1/2 turn and re-torque in the recommended pattern. And lubing the the nut contact face also reduces the friction further aiding more accurate torque figures.

I've only done one re-torque on my 850 and still no oil leaks/seepage. Thats on the dreaded Comecic head gasket too. It's done a track day too, without an oil cooler and still no problems. It did burn a bit of oil though with the extra heat. An oil cooler is going on before the next track outing.

[Ponderosa]

Clean and lube...

I always have cleaned and used a graphite lube on threads, torque, back off, re-torque.. Having a good calibrated torque wrench is a must, I use never seize on exhaust bolts, longterm, unlike metals.. I have seen unlubed, single torqued bolts and nuts vary in re-torque from a little to a lot.. Oh, once you have the seep, it usually does not leave after re-torque.. Sorry, just observation... Rays right, sounds like he has been wrenching many moon...

[doctorgonzo]

Threads were clean, it's about a $100 torque wrench (not a $29.95 pep boys special). The loosest bolts were inner ones. It is (as Ed mentioned) an Athena gasket from one of the $60 "complete" gasket sets. We'll see how it goes when the summer heat gets here. Pretty much all these heads are going to weep a little anyway after a bit of riding. They get too hot and move around too much not too. If the little weep it showed is as bad as it gets, no worries.

[Dogma]

Torque itself is not what we really care about in a threaded fastener. Tension in the fastener is what we want, because that's what holds the joint together. According to my engineering textbooks, empirical research has been done on this topic. Measured (not theoretical) tension in the fastener is not significantly increased or decreased by lubricating the threads. What lube does do is improve the correlation between wrench torque and tension induced in the fastener. So, lube makes the torque wrench more precise as a measure of how much tension is in the fastener. No other impact on how tight the joint is. Obviously, clean threads are prerequisite to lube being significant.

On the subject of backing off 1/4 turn before re-torquing: The structure of the head should prevent separation of the sealing surfaces as long as you don't loosen the whole head. Even if you did, you'd have to move the head to break any seal, and if it's been on there long, it's probably stuck down. I suspect normal thermal cycling of the engine is more likely to break a seal.

This spring I put a Vesrah gasket on my 850 (with the OEM base & oval rings. Thanks again bwringer). I re-torqued after about 600 miles of slab & WV rally, and only one or two nuts moved as much as 1/4 turn. Most of them had to break loose again, but had not loosened. I broke them loose in the tightening direction for no reason I can recall. After relaxing the wrench, they immediately clicked when I tried to tighen them further. (I'm not recommending that, just reporting. Having thought about it, I'd loosen next time.) No leaks 1000 miles later.

[DimitriT]

Make sure the motor is as cold as you can get it.

[posplayr]

Torque itself is not what we really care about in a threaded fastener. Tension in the fastener is what we want, because that's what holds the joint together. According to my engineering textbooks, empirical research has been done on this topic. Measured (not theoretical) tension in the fastener is not significantly increased or decreased by lubricating the threads. What lube does do is improve the correlation between wrench torque and tension induced in the fastener. So, lube makes the torque wrench more precise as a measure of how much tension is in the fastener. No other impact on how tight the joint is. Obviously, clean threads are prerequisite to lube being significant.

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I agree with most of this except for

Measured (not theoretical) tension in the fastener is not significantly increased or decreased by lubricating the threads.

The whole point of the thread is how to get a more accurate tension in the tensioned bolts. Other than calibrating your torque wrench there is only one way and that is to reduce the friction during the torque-ing operation.

Two factors reduce friction:

1.0 lubrication : for retorque-ing a head, I don’t know that pulling the bolt out and re-oiling it is necessary. Although pre oiling during assembly appears to be good practice.

2.0 Staying out of the stiction regime. Friction is minimum when the bolt is moving slowly. In order to re-torque, it has to be backed off and slowly torqued.

Both of the above are more accurate because they minimize torque related to friction which takes away from the torque required to tension the bolt.

This is shown graphically in the attached.

Mystery solved.

[waterman]

I have always wondered if when torquing nuts, should they be tightened in stages. For instance, if needing to torque head nuts to say 19 lbs/ft, would you first tighten nuts sequentially to say 12 lbs and then finish torquing them to 19 lbs. I know when tightening the clutch bolts, it is recommended to evenly tighten bolts before final torquing. If you do go by steps is there some accepted value (say 75%) before final settings.

Sorry, if I am threadjacking.

[posplayr]

I have always wondered if when torquing nuts, should they be tightened in stages. For instance, if needing to torque head nuts to say 19 lbs/ft, would you first tighten nuts sequentially to say 12 lbs and then finish torquing them to 19 lbs. I know when tightening the clutch bolts, it is recommended to evenly tighten bolts before final torquing. If you do go by steps is there some accepted value (say 75%) before final settings.

Sorry, if I am threadjacking.

I guess it depends, but you want the two mateing surefaces to join uniformly so tightening in a crossing pattern as described by the manaufacturer is always recommended. Ray says he goes in 10 ft-lbs steps on a head torqueing sequence.

It would not hurt to add a 5 ft-lbs setp like; If going to 30 ft-lbs go 10,20,25 and then a final 30.

[posplayr]

Thats on the dreaded Comecic head gasket too.

It has been determined by unofficial technical personal that the Cometic 1166 MLS gasket is defective in that the high and low pressure oil passages have reversed embossing in the gasket.

It is highly likely that any 1100 derived MLS gasket has the same tooling issue and shoudl be suspect. Cometic would have probably used the same template and only change the diameter of the bore.

Oil passages on your 8V motor are likely different and the MLS was laid out different.

[posplayr]

Make sure the motor is as cold as you can get it.

Did not think of that but I did the retorque when I did the valves so it was stone cold for that.

[Agemax]

lots of different answers and theories on this subject.
i personally will stick to my own tried and tested method that i was taught as a young apprentice.
another example of what is right and what is wrong but if it works for you, then what the hell

[Nessism]

lots of different answers and theories on this subject.
i personally will stick to my own tried and tested method that i was taught as a young apprentice.
another example of what is right and what is wrong but if it works for you, then what the hell

Lots of people doing the WRONG thing from a technical perspective, justify it in their minds by saying "works for me".

It's pretty much irrefutable from an engineering perspective that the bolt should first be loosen up from it's static position before attempting to retorque it. I've been involved in torque surveillance auditing in two different auto assembly plants, from different manufacturers, and both did basically the same thing: mark the static position of the bolt, back it off, then make it up while taking note of the torque when the fastener moved past it's original marked position. The amount of torque to get the fastener moving was almost always greater than the torque when making up the bolt to its original position.

Regarding lubing the threads, this will allow the fastener to turn smoothly thus minimizing friction due to the threads. In some cases this will result in more clamp load on the parts, but never less. For critical parts like connecting rod fasteners, some high end engine builders measure bolt stretch instead of worrying about torque since there is less risk this way due to inappropriate readings due to bolt friction. For our GS engines, I strongly recommend cleaning the threads on all fasteners and then applying either some anti-seize or oil to the threads. Both of these compounds will reduce the amount of corrosion that will set up inside the threads which is more important than relatively minor differences in clamp load due to the oil itself.

[doctorgonzo]

Off topic, but since we have the engineer brain trust in residence...

I never thought about this until yesterday. I've been a subscriber to the "slappy valve is a happy valve" school. Thinking nothing about setting one at .1 rather than leave it at .04. When I initially adjusted my valves on assemble I set some WAY loose (in the .11 to .12 range) just to get it together (shim shortage). I adjusted them all back to within spec yesterday (and didn't spit a shim in the 200 miles of break in ride thank god)..

My thought (which as I always say is dangerous) is, that would change the effective lift of the cams right? a .310 lift cam on a valve that was at the loose end would be effectively lifting less that a valve at the tighter end of the range.

Am I thinking correctly?

[posplayr]

It's pretty much irrefutable from an engineering perspective that the bolt should first be loosen up from it's static position before attempting to retorque it.
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Yea i cringed when the discussion veered toward actual measurements v.s. theoretical

I've been involved in torque surveillance auditing in two different auto assembly plants, from different manufacturers, and both did basically the same thing: mark the static position of the bolt, back it off, then make it up while taking note of the torque when the fastener moved past it's original marked position. The amount of torque to get the fastener moving was almost always greater than the torque when making up the bolt to its original position.

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The static load loosening (the break away) was greater than that requried to restore Right?. I'm not an ME but when I played with the torque wench that is exactly what seemed to happen. The wrench made a loud crack sound when lossening that did not occur on tightening.

[Dogma]

I agree with most of this except for



The whole point of the thread is how to get a more accurate tension in the tensioned bolts. Other than calibrating your torque wrench there is only one way and that is to reduce the friction during the torque-ing operation.

...

I may have been ambiguous in my choice of words. I wasn't trying to make a new theoretical statement. I was only trying to report that, in tests, bolts tightened to a specific torque reading, did not show any significant change in average tension induced when lubricated. What they found was less spread in the data for tension actually induced at a given torque wrench reading.

The article quoted in my textbook is in a back issue of Machine Design that I'm having trouble finding on-line, though I thought for sure they had back issues available (J.C Blake and H. J . Kurtz "The Uncertainties of Measuring Fastener Preload," Machine Design, vol. 37 Sept. 30, 1965, pp. 128-131).

Here's the pertinent data though: 1/2-20 UNF bolts tightened to 800in*lb, dry and lubricated. Mean tension induced for dry bolts was 34.3 kN with a standard deviation of 4.91 kN. Mean tension induced for lubricated bolts was 34.18 kN with a standard deviation of 2.88 kN. The dry bolts ranged from 23.6-42.7kN, and the lubed bolts ranged from 30.3-40.5kN.

I double-checked the quoted figures, and yes, the lubed bolts induced less tension on average, but by an amount lost in the variability of the test. The principal conclusion of the study was that lubricated bolts are imperative for maximizing consistency. Even so, the standard deviation for lubed bolts is almost 10% of the mean. For really critical applications (none of those on a GS), you need a method of measuring bolt tension directly.