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('07 Cobalt LS, vanilla 2.2, 70K mile)

Putting the timing chain cover back on. [1] One bolt goes through the cover into the water pump. Initially, it threads OK (not cross-threaded); But, when I get near (but still definitely below) the spec'd torque, the torque stops increasing, while the bolt continues to turn. It feels 'stretchy', like something bad is going to happen.

This looks to be an ordinary M8 bolt. Torque spec is 18 lb-ft. The water pump is probably aluminum.

I'm inclined to let it go where I am, around 15 lb-ft. But, it doesn't seem like the spec should be anywhere close to a failure point. So, replace the pump?

Update: No problem: I just pushed through, and the torque came up to spec. My guess is it was flatlining while it pulled the middle of the timing chain cover up against the boss it sits on.

[1] After a timing chain problem. Nothing was done to the water pump or its bolts or its (separate) chain.

  • Perhaps the thread is stripped and can't take full load... is it holding a gasket? if not, then you might be lucky... – Solar Mike Nov 11 at 5:09
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    Remember, that torque is only a measure of clamping force which is really what you're after. But this depends on the threads working properly, i.e. smooth and solid. If the bolt threads don't slip or hold as they are designed to do then you won't get the clamping force even if the torque is correct. I'd say if you have a hunch the threads are stripped then get started on a re-thread w/ a helix coil. BTW, I always double check the spec at this point. And I'm assuming your tourqe wrench is calibrated correctly. – Elliptical view Nov 11 at 6:08
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M8 fasteners are generally both common and cheap. If in doubt about the condition of yours, you can buy a new one in a hardware store.

To eliminate gasket as the cause, thread the fastener into the water pump body without the cover and see how it engages.

  • Just for the record, (1) the bolt is not a standard length, such that either 100 or 110 mm bolts would be problematic WRT thread engagement; (2) it appears to be coated, which may be necessary for a steel bolt going into aluminum; (3) my concern was for the water pump's aluminum casting, not for the (steel) bolt. I finally just went ahead and cranked on it, and the torque came up. I'll update the thread when/if nothing blows up when I run it. – George Nov 19 at 21:26

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