Thread Repair of S70 Mechanical Belt Tensioner Bolt Hole. Helicoil, Time Sert, Form A Thread?

Post by **Electrix** » 16 Jan 2020, 16:17

Here's the situation I'm trying to resolve. I overtightened the tensioner bolt and about 2 weeks later the tensioner loosened, the belt slipped and the intake valves bent. Right now, the valves are replaced, the engine is back together and it's almost time to turn the key and let it run.
The remaining problem at this point is that my tensioner bolt hole Helicoil repair doesn't seem to have gone right. The bolt went in, but was harder to turn than it should have been. When turning the crankshaft with a wrench as a test,the belt tended to slide on the tensioner, moving toward the engine while staying in place elsewhere on it's path.
My guess is that is bolt ended up sitting higher at it's outside end than on it's inside end, causing the tensioner to lean slightly and leading the belt to slide off,though it seems straight just looking at it. I'm installing a new tensioner so it should be good, but having bought a defective one is not impossible.

I'm considering a few different options to correct this -
1) Remove the Helicoil, re-tap the hole, insert a new Helicoil (No cost at this point, but more aggravation)
2) Remove the Helicoil and re-drill/tap etc for a Time-Sert (Likely a better idea,but about $80+ for the kit)
3) Permatex or Loc-Tite Form-A-Thread (Not sure if these would be appropriate for this application)
4) Leave the Helicoil in and add thread former for more support throughout the hole.

The big problem with drilling into the front of the engine is the simple fact the there isn't enough space to work in. There is 3 1/2 inches between the hole and the inner fender - barely enough to fit a hand into. How can a hole be drilled without the possibility of it ending up angled incorrectly? Aside from lifting the engine out of the car, how can access to the front of the engine be improved?
This is the last major step in getting this job completed, and after putting a lot of time and money into it I'd really like to get it finished and running.

Post by **Electrix** » 16 Jan 2020, 16:20

I forgot to mention of other option being considered -
5) Install a hydraulic tensioner

Post by **volvolugnut** » 16 Jan 2020, 17:32

Can you access the hole by removing the fender well or cutting a hole in the fender well? I think you have identified the problem. It is likely drilled crooked because of poor access. IF you can get the hole straight, then you can add a larger bolt by tapping the larger hole - no Helicoil needed.
volvolugnut

Post by **Electrix** » 16 Jan 2020, 17:53

volvolugnut wrote: ↑16 Jan 2020, 17:32 Can you access the hole by removing the fender well or cutting a hole in the fender well? I think you have identified the problem. It is likely drilled crooked because of poor access. IF you can get the hole straight, then you can add a larger bolt by tapping the larger hole - no Helicoil needed.
volvolugnut

A larger bolt probably wouldn't fit through the tensioner, and I would still need a way to ensure that I was drilling/tapping straight.
The outer fender could be removed but the inner fender (I'm not sure of the correct term for it) would still be in the way. This could be drilled or cut through, but there is a metal pipe that might be the fuel line in the area that I'd be cutting, as well as an electrical conduit. There is also a raised area - a roughly square length of metal that appears to be there to stiffen/strengthen that area that I'd have to go through that to get to the hole.

Post by **volvolugnut** » 16 Jan 2020, 18:12

It may require pulling the engine. I can't think of another way to get access to get a straight hole. Perhaps someone else will have a plan.
volvolugnut

Post by **abscate** » 16 Jan 2020, 18:35

I believe the later blocks do not have the mounting holes for the hydraulic tensioner, so confirm that if you choose that route.

I would pull the engine

Post by **FlyingVolvo** » 16 Jan 2020, 19:43

I did this on my car last year, but caught it before I started the engine. Had car towed to a good Volvo shop and they used TIME-SERT. Highly recommend it, it's been solid. You only get one good shot at it or else the engine is probably done.

To do this right, you really need drop the engine/trans down. Like you said, not enough room to properly do it otherwise.

Post by **Electrix** » 16 Jan 2020, 20:22

I'm definitely leaning toward using Time-Serts. I think the hole that has to be drilled for one is slightly larger than for the same size Helicoil, so whatever's happened with the Helicoil installation shouldn't effect the outcome of a Time-Sert installation.
Something I hadn't thought to check on... removing the plastic fender skirt and raising the car on a jack. There might then be more room to work when going in from underneath. Might check on that tomorrow.
It's odd that there seems to be no gadget made that would facilitate drilling in a straight line in a situation like this. And people have been drilling into things for a few thousand years now.

Post by **FlyingVolvo** » 16 Jan 2020, 20:46

I believe that's what the shop did to mine. Due to its alignment against the frame, they still had to drop the engine, but only a foot or so. I think then removing plastic fender in this case gave the needed room. It's involved, but not as bad as fully removing the engine/trans.

Here's what mine ended up looking like.

Stu70 · Post by **Stu70** » 18 Jan 2020, 04:11

However you manage it ,Timesert over helicoil every time. Helicoil lines a worn thread, Time sert is a new thread. Follow instructions (use good oil) and it’s $80+ of insurance well spent. Plus you’ll always find more worn threads.