Torque wrench broke head bolt. This sucks.

[D2Cat]

"twisting the bolt incrementally" should not have an impact on getting the bolt too tight.

If you question your wrench you could go first 20#, then just move up to 25#. Then you might have an idea if your wrench is clicking to indicate the slight increase. If you torque through the correct sequence, it would not make any difference to how many times you went through the process to get to the final torque value.

To make you feel better with more confidence, you could go to your local auto parts store and rent their torque wrench to compare to yours. They usually just require a deposit and you get it all back when you return the tool.

 

[bxray]

Here is a way to test the wrench.
You could use bar bell weights.

http://m.wikihow.com/Calibrate-a-Torque-Wrench

Ray

 

[lugbolt]

Also depends on the lubricant used on the threads and under the bolt head. I'd have to go back & look at the WSM, but I don't think they want any lube on them. I don't remember the WSM stating either way, so dry is fine.

Adding lube will change the stretch of the bolt, by making it "easier" to tighten the bolt. On rod bolts, I'll check the stretch, say, .0015", which just happens to be 70 lb-ft (dry). Put another one in with 30wt engine oil and it might only take 60 lb-ft to get it to stretch .0015". Or put ARP's assembly lube on one, and it might only want 50 lb-ft to get the exact same stretch. For these reasons, I can see it being entirely possible to break a bolt by using lube where it's not supposed to be used, or the wrong lube. Even 20w50 will affect how a bolt stretches differently than 10w30. That stretch is what holds the parts together, kindasorta like a spring pulling the head down to the block. Too much stretch, it goes pop. Not enough and the bolt backs out and/or the head lifts from the block.