Method of torqueing

[gost]

Can anyone confirm what the method of torqueing by degrees of turn, 2 stage torqueing, is exactly. The manual calls for this and I need to re-torque my head bolts for one cylinder that has a slight leak at the head/cylinder mating surface. Manual say's that
all Carrera engines 84 and up to torque using the method of by degrees of turn 2 stage tightening. Stage 1=11ftlb stage 2: 1x 90 degrees +or - 2 degrees in sequence.
Does this mean to: Stage-1- torque bolts to 11ft/lbs and Stage-2- continue tightening for 90 degrees of wrench travel or 1/4 around from that point?
Also can I loosen the 4 head bolts and re-torque them on the one cylinder only without a problem, following the correct sequence of course?

Thanks again!

[ChrisBennet]

Yes, you've got the idea.
Step 1: torque all head bolts to 11 ft/lbs
Step 2: turn each nut 90 degrees further

The object of tightening a fastener is to put a certain amount of tension on the fastener. The most accurate way to measure this is measure how much the fastener stretches. Obviously that isn't too practical (or necessary) for most fasteners.

In place of measuring fastener stretch, the torque to tighten the fastener is used instead. This is pretty easy to do but the downside is that the actual torque applied can vary by up to 80% due to differences in friction. The higher the torque the more effect friction has.

The torque angle method is used to torque a fastener up to a low torque/low friction effect starting point before stretching the bolt further by turning the nut X degrees.

[rant]
Torque is a very crude method for tensioning a fastener. A nice torque wrench with 2% accuracy means nothing if you are using a rusty nut and washer with no lube vs new fasteners w/30 wt oil or fasteners that aren't rusty but have been made smooth by mulitple uses. In other words, IMO people concentrate too much on the accuracy of the torque wrench when they should be more concerned about duplicating the conditions under which that torque spec is valid.
[/rant]

To answer your 2nd question, it would probably be better to remove all the head stud nuts and the retorque. However, (speaking as someone who already has reserved seating it hell) I would just remove the 4 nuts and their washers, rub the top of the washer and the bottom of the nut (the friction surfaces) on some 600 grit abrasive paper. Clean them off and then apply a little antisieze (Optimoly HT) to the bottom and threads of the nut and torque angle them in a star pattern.

-Chris

[gost]

Makes total sense. The old/rust factor would definitely provide inaccurate readings with just a torque wrench. Although the angle method would also be subject to the same variances. Seems like, and I agree, that getting the bolt tight to a certain tolerable small range is sufficient. It just can't be spot on especially using old hardware as you mention. I will remove the 4 bolts and clean them up as you describe. I will leave the remaining head bolts alone. I could smell disaster in the air with that one.
Thanks so much for your thorough response Chris. Brought back memories of my Strenght of materials course in College.

Respectfully

Gordon

[ZOA NOM]

Great info, and stuff I never really considered. You learn something new every day. This is an example of why my time on this board is never "wasted" time.

[rcecale]

Originally posted by ZOANAS
You learn something new every day. This is an example of why my time on this board is never "wasted" time.

Zoanas,

Can I use that line on my employer?

Randy

[ZOA NOM]

Give it a shot. It worked (sort of) on my wife.

[David]

FYI. From the Machinery's Handbook:

Accuracy of Bolt Preload Application Methods:

By feel ±35%
Torque wrench ±25%
Turn-of-nut ±15%
Preload indicating washer ±10%
Strain gages ±1%
Computer controlled yield-point sensing wrench ±8%
Bolt Elongation ±3-5%
Ultrasonic testing ±1%

[gost]

Where do ya fetch one of those ultrasonic testers? Might as well go all the way if I'm going to get anal about the car. Can use it to clean the SO's jewelry as well...ha!

[ChrisBennet]

This is excerpted from some Raceware information. As you can see my memory was faulty (about the 80%). Sorry about that. Hope you find this as interesting as I did.
-Chris
--------------------
Torque Friction & Fasteners
(2nd page)

When you use a torque wrench to install a threaded fastener, the wrench is
actually used to apply and measure a force. The force is designed to
PROPERLY tension the fastener so it can perform it's job properly. If the
fastner is under or over tightened, it will prematurly loosen or fail.
Torque wrenches do not measure TENSION, they measure TORQUE. In the case of
a threaded fastener, torque is the radial force applied to overcome
friction in the threads and to streach or tension the fastener.

In quality threaded fasteners as much as 80% of the torque applied to
tighten them is used to overcome the friction in the threads. Only about 20%
of the force is used to actually tension the fastener. That means that any
change ins the FRICTION has DRAMATIC effect on tension. All quality
fasteners have specific installation instructions that dictate what
lubricant if any should be used when tightening the fastener. Lubricants
such as motor oil, anti-seize, moly lube, cam lube, STP(tm), ect, ALL have
different friction characteristics.

USING THE WRONG LUBRICANT CAN CHANGE THE THREAD FRICTION BY AS MUCH AS
30%, CAUSING A FASTENER TO BE IMPROPERLY TENSIONED.

Thread design and pitch also have a great effect on Torque and Tension.
Fine threads exert a greater tension on a fastener for the same amount of
Torque applied. This is because of the angle on the threads is smaller and
therefore the 'wedge" effect is greater. Thus if you tighten a fine thread
fastener to the same torque as a coarse thread fastener, the fine thread
fastener will have a higher tension, and clamping force. (clamping force is
the force created by a fastener that holds two or more parts together.) Due
to the difference in friction and "wedge" effect, fine threaded fasteners
are often tightened to a LOWER torque the coarse threaded fasteners, to
prevent over-tightening and failure.

Friction in a threaded fastener assembly is effected by many variables
including but not limited to: thread design, thread pitch, lubricant,
smoothness of surfaces, if a washer is used or not, LENGTH of thread
engagement, and fastener design, (i.e. a bold verses a nut), just to name a
few. When a bolt is tightened into an existing hold like a block or head
installation, friction is present at BOTH the threads and the bolt head. The
length of the thread engagement effects friction and torque. A nut has
considerably shorter, (in most cases), thread engagement than a bolt.
Therefore it is not necessary or desirable to tighten a nut to as high a
torque as a bolt, because the nut has less friction to overcome to
properly tension the fastener.

[randywebb]

Good info, but Raceware needs a better proofreader:

'Friction ... is effected by many variables'

[David]

We have an ultrasonic bolt length measurer at work. Unfortunately it only works on relatively large diameter bolts, and bolts under a few feet in length as I discovered the other day .