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Discussion Starter · #1 ·
Four years ago when I last did my timing belt, I accidentally overtorqued the lower nut that mounts on the stud. I felt it go soft and it's been keeping me awake at night for years. Well today I removed the tensioner to do the belt again, and it backed the stud out and some threads came with it. Ordinarily I would chase the threads with a tap, but this goes into the oil galley. What can I do? I'm going to be devastated if I lose an engine from a shaving going through it.
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2015 Chevy (Holden) SS, 1989 Milano (Shankle Sport), 1991 164S
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Heli-coil the threads?

You use heavy grease on the helicoil tap to catch the cuttings. You run it in only a little way and then back it out to clean the hole and tap, then regrease and run it in a little further. The greased tap tends to take the cuttings out with it, the cuttings in the greased flutes of the tap. Do this a few times until you have tapped the hole sufficiently prior to inserting the coil.

I had to do this when I helicoiled the sparkplug holes in my Sprint GT, head on. Worked just fine, I was surprised how well it worked. Put another 100k miles on that engine. The cuttings were always stuck to the tap. But I do realize this is into an oil galley, not just a combustion chamber where any possible shaving remnants get blown out the exhaust, so you have to be meticulous. Use a cotton swab to try to further clean the tapped hole.

As an aircraft mechnic, my father had used this method sometimes in the old days in order to save an engine. He was not worried about it.
 
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This is easily repairable if threads are even damaged enough to warrant it. Suggest to vacuum that hole out briefly with shop vac and clear out for a better look. I bet it's not necessary to replace the threads. Chase threads and see how it looks. I use this product all the time: https://www.amazon.com/Lang-Tools-2584-15-Piece-Restorer/dp/B000XJ48V0

Get the threads clean, dry, install the stud with some good locking compound.

Helicoil is an option here if threads are ruined but I doubt it's that bad. If possible you could install a small scrap of cloth as a tampon into the gallery if you are confident to extract it after tapping. It will keep shavings from traveling inward. Extract with hemostats, pick, or tweezers. I have used this method in other sensitive areas successfully.

Obviously both studs are important, but that top pivot stud/ nut doesn't need a whole lot of torque. The lower stud is the one that needs to lock the tensioner positively and prevent sliding into a different position. Speaking of that, the lower stud doesn't look too great... suggest repair or replacement.

One more thing. Pull that spring bracket out on the timing cover. Its' only used on the hydraulic tensioner. :)
 

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Discussion Starter · #4 ·
Thanks guys, I'll get it good and clean and see what it looks like. Does anyone know if that oil galley is upstream or downstream from the filter?
 

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While the stud nut may not require a high torque, you do not want the stud working/backing out some time later due to thread material fatigue damage. It is a pivot arm, taking side loads and tension, esp if overtorqued. I'm sure the remaining threads are already compromised. You've already lost a few.

I had to helicoil the threaded holes for the serp belt tensioner swing arm bolts on my 91S. Although these were bolts, not studs, which did make the thread degradation worse, threads in aluminum just do not hold up, usually developing fatigue cracks. The grease method worked well, capturing the cuttings.

IMO, I think that if I were to rebuild an engine with an aluminum block, I would helicoil (or whatever) every threaded working hole in that block, provided there was sufficient edge margin of course.
 

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When it comes to these engines, racingswim knows what he is talking about. Note especially his point that the load on the upper stud is miniscule compared to the load on the lower stud.
 

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Discussion Starter · #7 ·
I've never had to do a helicoil before, so this is a hell of a place to start. I mostly worry about drilling the hole straight, plus the shavings from drilling. I'm inclined to clean up the threads. I'll definitely replace that lower stud too, hopefully it doesn't fight me too much. Never done a helicoil before and this is a hell of a place to start. I've got an old junk BMW cylinder head to practice on, but I really worry about the shavings generated drilling for the heli tap.
 

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"Note especially his point that the load on the upper stud is miniscule compared to the load on the lower stud:

Uh, you have to keep in mind action and reaction. The loads at one fastener location have to be reacted at another, plus the belt.
 

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I know what he is saying. It's a three reaction body until everything is torqued up.
 

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OK. Misunderstood.

BTW, one does no drilling when doing a helicoil job. Just use the oversized tap which comes with the kit. It works, goes in straight. No drill needed or supplied. The cuttings are caught by the heavy grease in the tap flute grooves. Then the coil is run in, and the installation end tab carefully broken off and removed with their tool or needle nosed pliers. Good to go.

Or, if you feel you cannot do this, just mix up some of the high strength version of JB Weld, smear it on the threads of the stud and run it in, letting it set for a couple of days. Later, tighten the nut with the minimum torque, using a nylon lock nut, or better, star washer. Probably good enough, at least compared to what you had.
 

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Discussion Starter · #13 ·
Palm Sunday, it's only fitting we talk about miracles. I disassembled they old stud that came out in the tensioner. The threads I felt let go years ago were the stud! Miracle that gave up before the block. Going to get a thread chaser, grease it up and run it through. This gives me more confidence in a good result.
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I'm amazed that steel threads going into aluminum would be buggered like that. The material strength being so different, it doesn't really happen. Something else going on. Maybe that stud was damaged before in something else and just put in, maybe because the PO had no other stud of that size?
 

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Discussion Starter · #15 ·
I've done the last two timing belt jobs. I know why the lower threads are buggered on the pivot. But I know this was clean, and went on clean, I had it on a stand when I resealed everything. Stupid torque wrench didn't click, and right when I though, this might not be right, it went soft. I cleaned out the threads with greased Q tips. Got some flakes but nothing crazy. I also removed the oil filter and after cleaning the threads very carefully, shot some kerosene in the hole. Moments later I saw it dribble out the center fitting of the oil filter. So bad news, it's downstream of the filter. But good news is if any shavings fall in there when I use the greased thread chaser, I may be able to flush them out through the filter passage. I'm feeling more confident this won't be a catastrophe.
 
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Discussion Starter · #17 ·
Update to this. I cleaned the threads with a grease covered q tip to remove and metal flakes. I ran a greased thread chaser in and encountered little resistance but the threads look much better. After more cleanup and a shot of kerosene through the hole to flush any possible bits out the filter housing I am feeling confident there shouldn't be any more trouble. Hopefully reassembled next weekend and back on the road.
 

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Sorry I'm late to this thread as the job appears to be finished. Better than a thread cutting tap would have been a thread forming tap ... no chips are created. The material is cold formed. This works especially well to repair cross-threaded holes.

-jim
 
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