Back off 1/4 or no on head retorque

[doctorgonzo]

Athena MLS head gaskets loosen up quite a bit. Hopefully you caught it in time.

Well, even at that loosness, I only had a barely noticeable weep on one side. It would have gotten worse of course.

[Agemax]

Well, even at that loosness, I only had a barely noticeable weep on one side. It would have gotten worse of course.

a decent gasket and a properly calibrated torque wrench then you wouldnt have even a slight weep

[Nessism]

a decent gasket and a properly calibrated torque wrench then you wouldnt have even a slight weep

Guess Doc and me both bought POS gaskets then, because they settled more than expected for both of us. Guess we'll have to buy a high quality cometic gasket like you next time.

[Agemax]

Guess Doc and me both bought POS gaskets then, because they settled more than expected for both of us. Guess we'll have to buy a high quality cometic gasket like you next time.

might help, saves problems later on

[rapidray]

you will only get an accurate torque reading with an accurate wrench on fasteners that are spotlessly clean and dry

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.

[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.