Can torque wrenches fail??

[CaptiV8ed]

I'm a little concerned about my torque wrench. I replaced my cylinder head gaskets ( 500Chimaera) as part of a cam upgrade very recently, and one of them has failed already (in 2 weeks) around one of the water jackets. They are meant to be torqued down to 70lbs/ft or 93 N/Ms which isn't particularly tight - However, before I build it all up again, is there a possibility that my torque wrench is under reading?

Any tips gratefully received.

Nick

[bluebottle]

It depends on the type of torque wrench..Mine has a thumb wheel at the end which pre-loads a tensioner spring to the desired torque setting which, if left torqued up in the cabinet will strength things and render it useless. the more common type or wrench i believe do not have a spring tensoner so shouldn't have this problem

[Stu R]

Certainly can. Depending on the make and type you can usually send them back to the manufacturer to be recalibrated. Something that should be done annually if they're used loads.
Or if it's just a cheapy one bin it and buy a decent one.
Spring fatigue is the most common reason for them going wonky.

[CaptiV8ed]

bluebottle said:

It depends on the type of torque wrench..Mine has a thumb wheel at the end which pre-loads a tensioner spring to the desired torque setting which, if left torqued up in the cabinet will strength things and render it useless. the more common type or wrench i believe do not have a spring tensoner so shouldn't have this problem

Bluebottle, the thumb wheel you refer to, is it as below?



Mine is the same as this one and I've had it for a good 5 yrs or so. I don't leave the thumb wheel tight, but could it be sh4gged?

Thanks for you help chaps!

Nick

[CaptiV8ed]

I'm thinking of going over to stretch bolts as we discussed in my leak thread. Now I've got it all in bits and can see that the head gasket is considerably buggered I wanna make sure this fix is permanent! 70lbs on my current torque wrench just doesn't feel tight enough. When I took out the original stretch bolts, I had to add some major leverage to undo them. The non strecth type at 70lbs doesn't fill me with confidence. Saying that though, the other side seems to have been ok.....

[methodwares]

two problems with head bolts.... one, they can stretch if re-used; two, they can bind slightly, and provide enough resistance to the torque wrench to get it to 'click' before they are fully seated and thereby not providing enough pressure on the head/head gasket to get a good seal. go for studs if at all possible.

[bluebottle]

[quote=CaptiV8ed]Bluebottle, the thumb wheel you refer to, is it as below?



Mine is the same as this one and I've had it for a good 5 yrs or so. I don't leave the thumb wheel tight, but could it be sh4gged?

Thanks for you help chaps!

Nick
quote]

Yep looks similar, Like all spring tensioned measuring devices they should be periodically callibrated. As said above a quick back to back test with another wrench will verify if its still reading true (I take mine down to a local garage once a year or so and get them to torque up a nut and bolt with their kit for me to check mine against).