Back off 1/4 or no on head retorque

[rapidray]

do not back the nuts off first! if you do it breaks the origonal seal created by the first torquing down.

Also NOT true! I back off each head nut, 1 at a time, 1/2 turn & retorque to final spec in the factory order on all of the street & race motors I build & have a ZERO leak record! Make sure you retorque each one you back off before moving on to the next one. Ray.

 

[Agemax]

NOT true!!! You will ALWAYS get a better, & more CONSISTENT torque yield on threads with a SLIGHT amount of oil on them! It reduces the resistance of the load on the threads when torquing. Ray.

disagree mate sorry, lubricated threads reduce friction and therefore allows the torque wrench to click off earlier. when the threads dry up thats when you find you need to tighten them up by one full turn and you wonder why you have oil leaks

 

[rapidray]

Yeah, ok, that's why all race motors are put together with lubed threads on the fasteners & DON'T leak! Read up on some physics & get back to me. Ray.

 

[posplayr]

Stiction in the threads typically causes a false torque reading, particularly on threaded fasteners that haven't moved in a while. Once you overcome this initial resistance for the fastener to move, the nut will tighten smoothly even if there was some corrosion creating a high amount of stiction.

Alright Ed I was waiting for this discussion. So the torque readings should definitely be performed in the Culombic friction regime?

That is why you have to back off.

For those that wanna know

http://en.wikipedia.org/wiki/Friction

 

[rapidray]

I was waiting for you Jim!!! Lubricating threads REDUCES friction, allowing MORE rotation of the fastener before reaching torque spec. The wrench clicks LATER, not earlier. Ray.

 

[posplayr]

disagree mate sorry, lubricated threads reduce friction and therefore allows the torque wrench to click off earlier.

Not sure how that works, assuming there is less friction due to lubrication then more torque is applied to the bolt tension before the wench clicks. Basically if you set your wrench to 30 ft-lbs and dry you have 5 ft-lbs of friction then the tension in the bolt corresponds to only 25 ft-lbs. If you grease the threads then the friction torque drops to say 2 ft-lbs then when the wrench clicks you have put 27 ft-bs into the bolt tension.

Lubricating the threads should always make the bolt tension closer to the torque reading (I know I am mixing toque and tension but I did not want to get too complicated)

As Ray described, go through each bolt in sequence back off then tighten till the bolt just starts to grab, then apply a smooth constant velocity slow pull (approx 1/4 turn in 2-3 sec) to the wrench till it clicks.

Even a cheap wench can be calibrated with a weight and string at the planned torque setting.


The wench is most accurate when friction is minimized. Oil goes along way toward that. However the technique above that keeps the bolt rotating allows you to stay out of the "stiction" regime, but minimize viscous friction so you only have the irreducible culombic friction. If the wench is stuttering (i.e. grabbing) then you are going to slow as that is you dropping into the stiction region by start stopping.

 

[Guest]

Not to throw a "wrench" into the works...

Is anti-seize a good lubricant for the threads, or should they just be oiled??

 

[Nessism]

disagree mate sorry, lubricated threads reduce friction and therefore allows the torque wrench to click off earlier. when the threads dry up thats when you find you need to tighten them up by one full turn and you wonder why you have oil leaks

I'm pretty certain the truth is opposite: lubricating the threads increase clamp load since the wrench will NOT click off because the friction in the threads is reduced. Some manufacturers of V8 engine connecting rod bolts even supply lube with the nuts to assure the nuts get properly torqued during build up.

 

[rapidray]

That is EXACTLY correct ED! All Carrillo rod sets come with lube for the rod bolts! I have friends that run Top Alcohol funny cars in NHRA & they use Anti-Seize. Ray.

 

[salty_monk]

I always read that you should not lubricate threads unless specified as with lube you will always OVER torque the threads for all of the reasons stated above.

Obviously I guess it has to be a "dry thread torque" but I belive they all are.

You also need to make sure the thread is clean.

 

[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...

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.

.

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.