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Tensioner Stud Bolt snapped


2005 Pontiac Vibe.

Silly mistake–I replaced a belt tensioner due to excessive vibration in the top part where it attaches to the engine. Whether the movement weakened the stud bolt first or I just used too much force – likely both but definitely the latter – it snapped off. It is the 12mm bolt not the big 17mm that goes through the belt tensioner.

I am having trouble finding a diagram online to identify if a) the stud bold is double threaded, which I assume it is, and if so b) would some vice grips + penetration fluid be enough to remove it possibly?

My other ideas were to use some metal/metal epoxy to fasten the threads to the new belt tensioner and then find a mechanic to tack weld it as well… If it helps, the belt tensioner sits flush with the broken bit of the stud bolt.

ps. edited for a bit of clarity and to remove imgur/outside links.
pss. very happy i did not go the expoy route before trying the obvious first steps.

It is not terribly clear, vice grips and PB blaster could work, though I prefer a small good pipe wrench. I would skip the epoxy solution.

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I don’t know, but aren’t some of these tensioner bolts left handed threads?

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Definitely worth checking, you need a new bolt anyway, buy one first and check.

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My understanding is the problem bolt attached the spring loaded plunger to the engine and I feel certain that bolt is a common right hand thread. The bolt that has often been left hand thread on idlers and tensions is the bolt that the pulley spins on.

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If it will fit in there, I’d try to get it out with a pipe wrench.

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Agree with Rod. Idler bolts can be left handed so that when the pulley turns, it doesn’t loosen the bolt is all. Use penetrant on there first like PB Blaster not Liquid Wrench, and take it easy so you don’t break it off. Better get the replacement first. It’s possible they used thread locker on it. I don’t quite understand why it broke unless corroded.

Or attempting to remove it lefty loosy if it is a reverse thread.

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Well that would explain why it snapped in the first place. Heh heh, guess that’s why we pay the pros.

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Ha! Well deserved, as I obviously over-wrenches it but in my defense the previous belt tensioner was popping like crazy and shaking the engine, hence the replacement, so MAYBE it loosened the bolt a bit for meh

Still no excuse—especially since it’s a nut that goes over it. Pulled down with my hand too quick and snap!

I appreciate everyone’s responses.

Looks like the stud labeled #3 in the below diagram. It is a stud, with M8-1.25 threads, 70mm long. GM replacement tensioners come with a new stud (or at least did at some point).


Using some CRC freeze-off and lock pliers I was able to, a fifth of a turn by a fifth of a turn, remove the bolt. I want to thank everyone for their help and responses. FInding a m8-1.25 replacement bolt is the easy part–thanks bugmenot.

In the future I will be more clear; was a bit shell-shocked I did such a silly thing and assumed the worse. Thanks everyone!

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Wonderful. Not as bad as about 8:00 at night breaking off a water pump bolt. Luckily a nut and a welder helped out.

Good for you for not yielding to that stubborn stud. Sometimes in that situation its possible to use a die to extend the threads onto the stud down further, then use back to back locking nuts to remove it with a wrench.

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When the serpentine belt tensioner mounting bolt snapped off on my 2002 Town and country, it snapped off flush with the block. No room to drill it out even with a right angle attachment without pulling the engine. Drove it to my mechanic, 1 1/2 miles away. He got it out, I suspect with a torch. Sometimes a pro is well worth the money.

I don’t think he charged me any extra for replacing the tensioner because of the snapped bolt. He knowa I do most of my own work and I think he enjoys impressing me. I have also have introduced a lot of friends and family to him.


Has anyone mentioned a reverse drill bit?

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Or an ez out ( which is never easy)

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He/him/them/it/er got it out a day or so ago, with a vice grips I think. Yeah break one of those dang easy outs in the hole and you really have a problem.

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Yup, it is out – we can close the thread. For those curious about what I was doing, here is a youtube video, if that is allowed: At the 25 second mark you can see how it slips on the bolt that I snapped.

I still think the old tensioner’s erratic up/down movement maybe weakened it a little bit!

I ordered a replacement Dorman bolt designed for cars and which is double-threaded but for now have a single threaded bolt I found at an autoparts store which is working just as well.

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