Torquing Head Bolts

[Shel_B]

There's a Project Farm video in which torque wrenches are tested for accuracy and consistency. It was shown that there's a fair amount of inconsistency with individual wrenches, as well as differences between brands.

How might these variations affect the quality of any head repair using a wrench that isn't at least consistent much less inaccurate? How important is it that all head bolts be precisely torqued to spec, or at least evenly torqued? How much variation can ruin a head repair?

Project Farm... Torque Wrench Test

'Were gonna test that"

bobistheoilguy.com

 

[zzyzzx]

I used a cheap Harbor Freight torque wrench on a head gasket job and it worked out fine.

 

[The Critic]

Head bolts only use the initial ft-lbs setting to seat the two flanges. The bolts generally use angle torque for the actual tightening.

 

[NYEngineer]

I believe it's more important to chase all of the holes in the block with a thread file and wire wheel the threads on the bolts if they aren't new. Lube and sealant where required... That seems more important to me than a couple percentage points of inaccuracy from the wrench.

 

[wpod]

I believe it's more important to chase all of the holes in the block with a thread file and wire wheel the threads on the bolts if they aren't new. Lube and sealant where required... That seems more important to me than a couple percentage points of inaccuracy from the wrench.

Indeed and well as cleaning and checking the flatness of the surfaces.

 

[atikovi]

Head bolts are supposed to stretch, so one time use. What about engines using studs and nuts? Are the studs and nuts reusable?

 

[Audiman]

Buy Stahlwille torque wrenches as they can be adjusted at both ends of the scale, have them calibrated every 6 months at least.

 

[kschachn]

Head bolts are supposed to stretch, so one time use. What about engines using studs and nuts? Are the studs and nuts reusable?

It depends on whether you take the stud past the yield point. However, some FSM give a maximum length value, so even if the bolt is torqued past yield you can still reuse it if the length is below a given value.

 

[Trav]

Buy Stahlwille torque wrenches as they can be adjusted at both ends of the scale, have them calibrated every 6 months at least.

A Stahlwille angle TW cost a good bit, min $1500 for a 1/2 drive to 200nm if bought in Europe, in the USA add a grand.

Stahlwille 713R Electronic SENSOTORK tightening angle torque wrench, size 20; 10-200 Nm, 1/2" + 14x18 mm

Stahlwille Tools 713R Electronic SENSOTORK tightening angle torque wrench, size 20; 10-200 Nm, 1/2" + 14x18 mm

www.kctool.com

 

[Asterix]

Some head bolts are torque-to-yield, so are single use. They get tightened to some low initial torque (ft-lb or N-m) then tightened finally in stages by turned angle. Some head bolts or studs are not torque-to-yield, so are tightened by torque (ft-lb or N-m), and can be reused.

Torque is generally not a good way to tighten threaded fasteners properly. It depends very much on the friction in the fastener threads and bearing surfaces. With proper preparation and specified lubricants, you can get good results.

You can spend a fortune and get a perfect torque wrench, NIST-traceable calibrated, but you are wasting your money. Simply breathing on the threads will change the bolt preload for a given torque.

Anyway, to give my opinion on the OP's question, consistency will be more important than actual torque. As long as the head bolts/studs are tight enough to clamp the head to the block hard enough, but not too tight to deform the head, it's good. But, I'd guess that consistent clamping across the head is more important once the minimum clamp is achieved.

 

[Job]

Somewhere there was video showing the way the torque wrench is used can cause a large amount of variation. When I tightened the head bolts on my Toyota 3 RZ engine I was surprised at how much power it took to complete the second 90 degrees rotation. I used a Felpro gasket which states made for the repair environment, which means to me it covers some defects better than a factory OE head gasket. The bolt stretch isn't much, 180 degrees on a 1mm pitch thread is .5 mm or only .020 in.
I got one of the digital adapters, the Delco one, to supplement and verify my torque wrenches. If both agree, which they did, then everything is highly likely to be ok.

 

[The Critic]

Some head bolts are torque-to-yield, so are single use. They get tightened to some low initial torque (ft-lb or N-m) then tightened finally in stages by turned angle. Some head bolts or studs are not torque-to-yield, so are tightened by torque (ft-lb or N-m), and can be reused.

Torque is generally not a good way to tighten threaded fasteners properly. It depends very much on the friction in the fastener threads and bearing surfaces. With proper preparation and specified lubricants, you can get good results.

You can spend a fortune and get a perfect torque wrench, NIST-traceable calibrated, but you are wasting your money. Simply breathing on the threads will change the bolt preload for a given torque.

Anyway, to give my opinion on the OP's question, consistency will be more important than actual torque. As long as the head bolts/studs are tight enough to clamp the head to the block hard enough, but not too tight to deform the head, it's good. But, I'd guess that consistent clamping across the head is more important once the minimum clamp is achieved.

During the angle step, my Techangle shows the final degrees turned and the "equivalent torque" that was required to achieve that turn. It is not uncommon to see 15-30 ft lbs of variation from bolt-to-bolt when doing head gaskets.

 

[thescreensavers]

Torque is generally not a good way to tighten threaded fasteners properly. It depends very much on the friction in the fastener threads and bearing surfaces. With proper preparation and specified lubricants, you can get good results.

You can spend a fortune and get a perfect torque wrench, NIST-traceable calibrated, but you are wasting your money. Simply breathing on the threads will change the bolt preload for a given torque.

+10000 that's why my HF wrench is great for lugs and Control arms..etc. As long as you don't use the top/bottom 10% of the tool and treat it decently there isn't anything extra to be had after a few bones. Imo Husky torque wrenches fit the bill very well for the quality to price ratio.

 

[kschachn]

Some head bolts are torque-to-yield, so are single use. They get tightened to some low initial torque (ft-lb or N-m) then tightened finally in stages by turned angle. Some head bolts or studs are not torque-to-yield, so are tightened by torque (ft-lb or N-m), and can be reused.

Torque is generally not a good way to tighten threaded fasteners properly. It depends very much on the friction in the fastener threads and bearing surfaces. With proper preparation and specified lubricants, you can get good results.

You can spend a fortune and get a perfect torque wrench, NIST-traceable calibrated, but you are wasting your money. Simply breathing on the threads will change the bolt preload for a given torque.

Anyway, to give my opinion on the OP's question, consistency will be more important than actual torque. As long as the head bolts/studs are tight enough to clamp the head to the block hard enough, but not too tight to deform the head, it's good. But, I'd guess that consistent clamping across the head is more important once the minimum clamp is achieved.

This is correct. Torque is actually a pretty poor surrogate for clamping force but it is easy to perform and is adequate in most circumstances. An expensive and sophisticated torque wrench is only giving you a more accurate measurement of an inherently inaccurate process.

 

[Audiman]

A torque wrench with adjustability at both ends allows you to ensure it is accurate over its full range. Cheap torque wrenches do not have this built in.

Any process is only as good as the person following it. It is the person that is the variable and that cannot be relied upon to follow the workshop manual/ proper process.

 

[Gimpy1]

Head bolts are supposed to stretch, so one time use. What about engines using studs and nuts? Are the studs and nuts reusable?

OEM are TTY. Aftermarket like ARP studs have their on install and torque proceedures and are reuseable. Studs still stretch, but they are made with different alloys and tensile strengths.