Big Dave

The WSM indicate that installing the nuts to the head studs is a four step procedure:

1. 20 Nm (15 ft lbs)
2. 90 degrees of rotation
3. 90 degress of rotation
4. 90 degress of rotation.

So...does this translate into:

1. Torque (in the proper sequence 1-10) the nuts to 20 Nm (15 ft lbs)
2. Turn (in proper sequence 1-10) the nuts an additional 90 degrees
3. Turn (in proper sequence 1-10) the nuts yet another 90 degrees
4. Turn (in propere sequence 1-10) the nuts a final 90 degrees.

In other words, no actual torque value is recorded for steps 2-4. It's just a matter of turning an additional 270 degrees after 20 Nm has been reached, in steps of 90 degrees each. Correct?

The WSM aren't clear on this, in my opinion.

Vilhuer

Correct AFAIK. That is normal way of tightening head bolts/nuts on many cars.

GlenL

That's what it means. torque-turn 90-turn 90

Not sure of the switch-over point, but the earlier engines had a three-torque approach, which I line better. Mainly because when re-re-re-torqueing the gaskets, I'm getting a known value. To make sure the head is tight, each day for three days after initial installation I loosen the bolts, maybe 1/4 turn, and then re-torque to the target value.

Doing this has three camps: the "not needed" folks, the "can't hurt" group and the "essential for high perf" sealots. I'm towards the last group with a dash of "after putting in all that time and $$$."

Not sure how re-torqueing would be done with the angle method. I suppose you'd have to take it back to nothing and start over. Anyone?

Tony

BTW. Its righty tighty Dave

What about reuse of head bolts?? is that recomended?

Garth S

For what it's worth, from Tohnichi Ltd ( torque tools), this convenient summary may give a little background:

"There are three ways to make sure that tightening is correct.
(A) Torque control method
Using hand torque tool (wrench or driver), or power operated torque tool (screwdriver or nutrunner) to tighten screws, nuts and bolts.
(B) Part-turn method
Bolts are tightened until joint surfaces are in close contact. At that point, just before solid tightening starts, nut and protruding bolt threads are marked to show their relative positions. Then, correct tightening is completed by turning the nut a half or 3/4 turn.
(C) Bolt elongation measuring method
When bolts are tightened at the same time, the elongation of the bolts are measured. "

The weakness of 'A' is that various levels of lube, crud, etc change the friction at the thread interface, and therefore the measured torque. A common measure of clamping force is tensile elongnation: 'C' is often used in open flange faces in chemical industry, and 'B' is favoured in heads [ eg. 928 WSM], for the bolt/stud stretch is known and maintained within the elastic limits of the fastner. ( eg. 3x90deg of a M14x1.75 is 1.31mm stretch). The initial 20 N.m applied is a predetermined gasket crush followed by three timed increments of fastner stretch, or so the theory goes ....

Big Dave

Well, it sounds like I've got the right procedure. Unfortunately, I need a new torque wrench. My current one doesn't go down to 20 Nm. Gonna have to get a very low range wrench to accurately measure 20 Nm.