Stripped tensioner pulley bolt hole


Hi… this thread is about a stripped thread.

I’ve been on here a lot lately, as I’ve been rehabbing a 97 Hyundai. While putting the new timing belt on, I somehow managed to strip out a portion of the belt tensioner pulley bolt hole. It must have been going in at a slight angle and I didn’t notice it. When I realized what was happening, it was too late. I pulled out about 3/8" of thread from the hole, wrapped around the bolt.

What can I do to fix this? Any help is greatly appreciated!


Heli-coil. Drill out the hole, use the helicoil tap to cut new threads for the insert, then install heli-coil to restore threads to correct size. The instructions will be with the kit. Available at any auto parts store.


There may be a means of doing this for this application that are different or better, but a common and trusted repair for stripped threads in general is the Helicoil:


I don’t think I can get a drill in there. Its on the front of the engine. I have about 4 to 6 inches of clearance. I have used small taps and dies… perhaps its possible to use a small tapping tool, the kind with the double handle to ream out the hole? Its aluminum…


They do make angle drills for tight areas like this.


I’m really not into running out and buying a new drill at the moment, but if I have to… if there is anyway to ream it out with a hand tool, I’d like to try that, first.


There is no other way. You’re repairing an assembly that needs some strength and if it fails it’ll strand you.
I know it’s too late now but when you’re starting a steel bolt into an alloy hole always run the bolt in with your fingers. You can tell if it’s cross threaded before all the damage. But don’t lose sleep over this because it happens to pro wrenches at times as well.

What needs to be done now is a proper repair. I much prefer Time-Sert’s to Helicoil’s. Helicoils can result in customer comebacks, which will kill a shop.

You’ll have to clean the area and get in there with a drill. You either remove the blockage (Radiator, shroud, fan or whatever’s in the way)and use a straight drill, or get in there with a right angle drill. It’s imperative you drill level and true and don’t go too deep (water jacket?). You’re drilling into alloy material so it’ll go easy, but take your time and do this part right. Next install the Time-Sert and lock it in. The result will be an assembly fastened as good as when it was new.

Watch this video for more information and prices.



I have just over 4" of clearance between the hole and the support for the motor mount. What kind of drill do you recommend? I was surprised he used just a hand drill in the video.


Can you remove the support?
Yes, use a hand 3/8" chuck drill.
Contact the Time-Sert people with the length and diameter of the bolt and they’ll send you everything you need to do the job.
It’ll cost a bit for everything you need, but a lot less than having the job done.



I’ve just read about a dozen threads on other boards for the time-sert vs. heli-coil debate. It seems slightly more folks like time-serts… I’ll give it a shot.

No, I can’t remove the mount. Its welded to the chassis. I just measured and there is about 4 and 3/8" clearance. Is there a right-angle drill that can fit into this space? I might be able to drill an access hole though the fender… I’ll look again tomorrow, but I doubt it.

Thanks for the help, its been a heck of an evening! I’ve attached a photo. The tensioner pulley hole is the hole in the center of the picture, just above the timing belt. You can see the space I have to work with.


Put a stick into the bolt hole and measure how deep it is. If you have about an inch of undamaged threads, that should be enough.
If the bolt hole is deep enough; but, the bolt is too short, go to an auto parts store and get the longer bolt. Make sure that the new bolt has the same strength markings on the head as the original. The number will be something like 10.5.


Rule of thumb I believe is depth of good threads should be equal to or greater than 3 times the diameter of the bolt. Anyone agree/disagree?


When you run into a situation such as this, one must use their imagination.

I see that the bulkhead is very close to the front of the engine. Why not take a hole saw and drill a hole into the bulkhead that is aligned with the stripped out hole? Now you can drill out the stripped hole and insert a Heli-Coil thread repair through the hole that was drilled. This may require purchasing a drill extension shaft to reach the hole with a drill bit. But that’s cheaper than purchasing a close quarters angle drill.



I bought a right angle adapter for my drill for just such occasions. It cost something like $15 so it was alot cheaper than a dedicated right angle drill. Saved me a number of times already so it’s paid for itself many times over. 4" isn’t much clearance though. You might need a stubby drill bit even with a right angle drill. I like the access hole idea as the next best option.


I decided to order a time-sert kit. Expensive, but it beats taking it to a shop, and definitely beats the possibility having a timing belt pulley come loose while driving! The bolt turned out to be a 10mm x 1.25. The tech I spoke to said I could probably drive the drill bit by hand with a 12pt. socket and driving tool(?) I also ordered a drill guide to make sure everything is perpendicular to the outer surface. The hole is 3/4" deep, so they are giving me a couple of shorter inserts (14mm) instead of the regular ones (16.2mm).

Thanks for the help!


Depends on material, TPI and load.

Here’s a neat generic calculator :