HF 1/2 torque for lugs - worst case?

[owenst7]

I find the responses about not using it on engines but lug nuts is good enough quite funny. Not good enough to keep your connecting rod on the crankpin but good enough to keep your wheels on your car, maybe?????????? Seriously, if it isn't good enough to keep your engine together, why would it be good enough to "maybe" keep your wheels on your car you use to haul you and your loved ones around at high speeds?

Coming from an engineer:
You need to learn when precision matters.
Do you use a pull scale to tie your shoes?

 

[Adam.C]

Do digital torque adapters ever go out of calibration (if not abused)?

No. I don't think the mechanism, if you can call it that, will ever go out of calibration. But a certain amount of adjustment is built in with respect to the handle, which one could theoretically disturb. My guess is, calibration of digital wrenches is a waste of money. All the big industrial users send their wrenches out. But they also send out mitutoyo digital mics. Beyond inspecting and zeroing, I'm not sure what service QA does to such tools.

Clickers rely on a spring to measure and react to torque. Beam type ditto. Over time, these springs can relax, take a set, maybe even work harden (they shouldn't). These tools do need to be calibrated.

The Chinese generally have problems with materials, and certifications for materials. I would expect that the spring steel inside a HF $10 torque wrench may not be to the same std as a US made wrench. I would also expect a lot more variability in the HF calibration. If you choose this wrench, maybe it would be a good idea to send it to be calibrated from new, then have it checked yearly or every 2 years to see how it is.

 

[Adam.C]

I find the responses about not using it on engines but lug nuts is good enough quite funny. Not good enough to keep your connecting rod on the crankpin but good enough to keep your wheels on your car, maybe?????????? Seriously, if it isn't good enough to keep your engine together, why would it be good enough to "maybe" keep your wheels on your car you use to haul you and your loved ones around at high speeds?

The engine assembly we are all worried about is the head gasket. All the seals need to be done carefully and accurately if you ask me. Rear main seal, even water pumps, oil pumps etc.

But the head sees a great deal of pressure, solely reacted by the head bolts. What we worry about is a combination of the tension on the bolts caused by the cylinder head pressure, but also the thermal effects of the engine heating up, the heads increasing in thickness stretching the bolts, then reducing head gasket pressure when cold, and the compression of the head gasket over time. All can lead to a lack of compression, performance and other bad things.

When you torque a head bolt, we are basically thinking of them as springs. As the load increases and decreases the bolts stretch, produce more resistance, then return to their original length. So first off, we want all the springs pulling at the same rate or we will create a weakpoint. Second, what we have found is the stretch shrink cycle often results in the bolts having less cold preload/prestretch than we thought. So we are now doing what is called TTY or torque to yield, where we stretch the bolts slightly beyind their elastic limits. When the gasket compresses, we are left with good preload. It also means the head bolts become one time use only.

Lug nuts are completely different. The wheel is held to the hub really through friction between the wheel and the hub, caused by the tightness of the lugs. If you lost lug torque, you would still have shear between the studs and the wheel. Cornering can put the lugs in tension, but only for a split second. They need to be tight and torqued together. They need to be in the ballpark but are otherwise unlike head bolts.

Still think this is funny?

 

[General Geoff]

Wheel/hub assemblies are designed to function reliably with the lug nuts torqued to a wide range of values. They are one of the most frequently loosened and tightened fasteners on the car, and the engineers who designed them know this, so they design it with a fair amount of fudge factor built in. +/- 25% of specified torque value in all the lug nuts on a given wheel assembly, will not likely cause a failure under normal driving conditions.

+/- 25% of specified torque on a cylinder head bolt, on the other hand, could very well be the difference between a perfectly functioning engine and a head gasket leak. Cylinder head bolts and other critical internal engine fasteners are less tolerant of sloppy torque values.