nickhance

I've got the head back from the machine shop, but it doesn't feel like the nuts are all torqueing evenly when applying the recommended torque (15-90-90).

Some of the nuts require much more force to turn that 90 degrees than do others. Do the head studs normally get weak, or has anyone else had this problem?

Does anyone have any idea what the problem may be?

Bri Bro

Did you skuff up the washers? They shouldn't turn when you torque the nut.

nickhance

no, I'll do that. But I don't think that would make a difference, would it?

Bri Bro

Yup, check the manual, they are very clear on this. The manual suggests you use some sandpaper to rough up the washer and the head and to also observe that it doesn't turn.

I use another approach, get a heavy file and hammer one side of the washer into it. This leaves a texture the same as the file on the washer. Never had one turn yet.

jabbadeznuts

Are you torquing by degrees? It would seem that a torque wrench would fix the uneven torques.

Bri Bro

Good point, there are two ways of doing the head torque in the manual.
New nuts, studs and washers.
1) 20Nm
2) 90 Degrees
3) 90 Degrees

Replacement (this is the way I always do it)
1) 20Nm (14Lbs)
2) 50Nm (36Lbs)
3) 90Nm (65Lbs)

Also,
-Always torque the nuts in the correct order.
-Apply a light coat of oil to the threads
-Insure the washer doesn't turn

jabbadeznuts

I ALWAYS use a torque wrench whenever possible. That way you KNOW that your spot-on.

Larry Parker

torque to yeild bolts ie torque angle
Yields a more even torque than torquing all bolts to the same number.............

Thats why they are used! I was told by and engine shop that built all the factory crate motors for GM, they switch to torque to yield bolt because there can be a 20% on head bolt with tradional torquing to a specific number.

Buy the tool to do it from snap on for 30.00 and you will have it for life!!

Larry Parker

Also they will not always feel the same.....even like they may be sliping in the block, but thats just the bolt yeilding to the proper tq number....

jabbadeznuts

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Larry Parker:
<strong>torque to yeild bolts ie torque angle
Yields a more even torque than torquing all bolts to the same number.............

Thats why they are used! I was told by and engine shop that built all the factory crate motors for GM, they switch to torque to yield bolt because there can be a 20% on head bolt with tradional torquing to a specific number.

Buy the tool to do it from snap on for 30.00 and you will have it for life!!</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">

Can you re-phrase that? It's very confusing. Why would not simply torquing each bolt to the specified torque not be as good?

Bri Bro

"Stretch" or TTY (torque to yield) bolts are used once and can't be reused. They are torqued to a value, then an angle torque (say 90 degrees) is added that stretches the bolt like a spring. TTY bolts are designed to stretch. The 944 doesn't use this method.

The "angle torque method" is the same as first torque procedure I listed above.

nickhance

So what does all this mean? Is it supposed to feel this way, or do I need new head studs?

Should I just torque them to 65ft-lbs in steps (mentioned above)?

nickhance

bump!

nickhance

Bump

Anyone have an answer for me? The rain has finally stopped and that asphalt is SCREAMING my name...

Danno

These are not TTY-torque to yield bolts. Which are typically used on engines with dissimilar metals for the block and head. This is a way to obtain similar torques on each bolt by removing all the elasticity in the material (on edge beginning of plastic deformation). These bolts typically have a smaller-diameter shaft to reduce their strength so the 'yield' point can be custom-tailored to the amount of compression force needed.

The studs in our blocks are not TTY and can be re-used up to a certain point. They do stretch permanently between the 1st couple of threads on the inside on each end based upon the numbers of times they've been torqued. This also stretches the 1st couple threads on the block and is one of sources of difficulty in removing the studs.

One of the biggest sources of error in bolted interfaces is torque and friction (check out <a href="http://www.boltscience.com/pages/basics4.htm" target="_blank">BoltScience-basics</a>). You want to follow the procedure in the book very carefully. Rough up the bottom of the washer and make sure the flat side faces down.

Use NEW nuts whenver possible. This is because the friction wears out the threads and can actually cause the nuts to strip out. Then oil the threads on the studs and bottom of the nuts as indicated in the book. At high-tension loads, the friction between the threads will throw off your torque-readings.

That's why with new studs and nuts, they recommend using the torque-angle method. That's because for any given thread-pitch and angle, each full-rotation yields a given amount of stretch and tension in the fastener. But because these are new threads, they will result in different amounts of friction and different torque-readings when tightened down to the same amount of stretch and tension.

One way to reduce this variation is to 'break in' the threads on your fasteners. Follow the second procedure and tighten each nut to the 36-lb•ft spec. and loosen them all up. Do this 3-4 times and you will have worn the threads of the nuts to match the studs. Then when you follow the #2 procedure above to 65-lb/ft, the torques will feel more similar between all of them.

BTW, also use only dino-oil to lube the threads, synthetics are so slick, they may actually not wear-in the threads correctly.