engine and drivetrain question on torqueing down a head gasket

[Guest Anonymous]

the final step in torqueing down my new head gasket has me warm up the engine and run it for 25 minutes then angle torque it 25degrees.

question - does anyone know if i let the engine cool or torque it with the engine warm? is suspect it's let it cool but i want to be sure.

thanks,

tim

[Guest Anonymous]

(nt)

[Guest Anonymous]

I agree, I would do it cold. Common (mechanic's) sense tells me that the purpose of this procedure is to "heat cycle" the assembly (and vibrate it) which may allow residual stresses to dissipate. Cooling then shrinks the parts, increasing clearances. You want that gasket to seal well when cold as well as hot. Stands to reason (to me) that you want to torque the fasteners at worst case.

But I could be wrong, if there is a trained mech here I will defer to experience and training.

[Guest Anonymous]

Seems I remember reading somewhere to torque it cold then drive it 500 miles and torque it again. Anybody else ever heard of this?

Phil

1970 2002

1991 E30M3

[Guest Anonymous]

you tighten it down cold, then heat up the motor which expands things (loosening them!), then you add just almost an eighth of a turn (25deg) which will cinch things down again... when it gets cold again, it will *tighten* up further as things shrink back down. just a guess!!

-Rob

[Guest Anonymous]

Rob, What's going to expand more, the steel bolts or the aluminum head. The starting length is nominally the same. I think Al has a higher coefficient of expansion than steel. Therefore as things cool they will loosen up, not tighten (by this logic).

I'm shooting from the hip. You are too. Both are equallly likely to be right because we both have some logical points. Most likely it's a compromise, considering many factors, some of which we haven't thought of. Looks like we need an experienced mech to set us straight. One with factory training.

[Guest Anonymous]

URL: http://www.bmw2002faq.com/store/index.html

when its hot, it should all be looser. when cold, it should tighten down some. i would think!

-Rob

[Guest Anonymous]

That what the factory manuals recommend. As for angle torqueing 25 deg when warm? Where did that come from?

BTW does anyone angle torque their 2002 head? And if so why? What degree? All my old shop manuals use standard torque figures....which I have always adheared to..... none list an angle torque amount.

WH

[Guest Anonymous]

it is a step torque, sorry do not remember the exact details, and it probably does not make alot of difference in terms of numbers for torque, but you use the torque sequence found in any Haynes manual, etc, and gradually increase the torque, first like 25 pounds, then 40, then final, like 55? DO NOT, I repeat DO NOT start the car when it is only say 40-45 and "heat cycle it". You will ruin all your efforts, coolant will seep into the cylinders and you will just start all over with a new gasket. The cryptic instructions on the gasket package are to be ignored. Call Metric Mechanic if you don't like my answer. (yeah I do know from experience). You may want to let it "rest" for some time between torques, especially the last step. And the degrees versus ft lbs method is about the same, if you watch you torque wrench as you do each step the degrees are about the same, BUT, the newer engines and NEW cylinder head bolts use the degrees method since the bolts stretch and are single use. I reused my head bolts (gawd forbid!!!!) but they can be (uh oh here starts a controversy). You did make sure that the oil etc was all cleaned out of each head bolt hole didn't you? a must, and do not over torque thinking it is better, and YES, do carefully check at 500 miles, set your wrench on very gently test that each head bolt is at the desired ending torque value. Do not back off and then tighten down, just smoothly evenly press ahead, wait to hear the click of the wrench. Good luck, smooth sailing, ,

[Guest Anonymous]

(nt)

[Guest Anonymous]

URL: http://www.hbci.com/~tskwiot/2002.html

(nt)

[Guest Anonymous]

I would agree with you on this... I've followed factory torque specs for 15 years and have done 10+ 2002 & 5 & 6 series heads in that time frame (yes I own alot of cars!). I've always reused the head bolts with no ill effects. They are not the "stretch" bolts that the newer cars have.

Now my 84' Audi calls for torque angle AND replacing the bolts. Something ridiculus like torque to 75 ft/lbs and angle torgue another 180 degrees! (must be like 120 ft/lbs on each bolt).I was afraid I'd break the damn things off....

WH

WH