Cambelt tensioner stud - stripped head

What is the best way to fix this without replacing the head?

I was adjusting the cambelt tension as its been whining like a supercharger since I changed the belt. I was careful not to overtighten it - I used the Haynes spec of 33 ft-lb, but it wouldn't tension. Eventually just spun and as you can see has stripped the thread inside the cylinder head


Thanks

 

Helicoil or v-coil should do the job. Just get correct thread pitch and size.

 

Thanks David - have been looking into helicoil this evening - I think I will give this a go

 

I think VW have a stepped stud for the newer diesels, that might work. ie M10 into the head and m8 for the tensioner.

https://www.ebay.co.uk/itm/403001861568

Like that.

Obviously you still need to drill and tap the head.

 

The stud is already M10. Looks like the Helicoil will be okay, but not much space to get a drill into the right place with the engine in

 

If I were a betting man I would suggest that’s been helicoiled previously.

 

You're right, my mistake, they are m10.

 

Yeah, I've not seen original metal come out like a spring before
Going to be fun getting the hole welded to then be drilled (square) and tapped in situ...
Failing that is it possible to helicoil to the size above the one you need, then fit the correct helicoil into the first one? Sounds dodgy (with a small d)!

 

Or…. Helicoil to the next available size and then get a stepped stud as mention by @Tristan ?

 

Helicoil will work well, if possible jack the engine as much as possible or get a right angle drill to drill the larger hole...rest is easy, tap, insert and drive the new helicoil and insert the stud as per original...

 

Its common if its been overtightened before...

 

It is possible the helicoil tap to go right in, without drilling first.

 

It appears from your picture that there is no thread in the hole. A helicoil needs a thread to turn into so you would have to re-thread the hole first. This would mean making the hole one size larger hence the stepped stud. Or…. Re-thread the hole and just use a stepped stud and then no need for helicoil. Clear as mud?

 

On even closer look at your picture it seems the helicoil was glued in with chemical metal. That was never going to last

 

Thats not a helicoil, thats how a stripped thread in aluminum looks like, threads are pulled right off.
If what is left is a hole 10.5-11mm no need to drill for m12.

 

Just tap existing hole for an m12?

 

If he gets m10 helicoil it needs m12 threaded hole. Of coarse thread pitch i believe is finer on the stud, needs checking, and buy apropiate helicoil kit. Kit has drill bit, special tap and the helicoil itself.
I once helicoiled stripped m6 thread, tapping with a regular m8 tap, but the bolt was very loose. So buy as a kit only.

 

So really he might as well get a stepped stud and not worry about the helicoil at all. Must be better

 

Thanks everyone. Its not been helicoiled before - the material that came out is non-magnetic. A normal M10 helicoil should work - i have a kit now and will be trying this in the next few days. Space is tight for drilling but should be okay. The head is pretty soft - i can almost get the helicoil tap to go in without drilling, but the current hole is a little small so will using the drill bit in the kit first just to make sure I get it 100% right. The stud thread is M10 x 1.5 and I have the helicoil kit to suit this.
Just need to work out what torque I should put the stud in at. The tensioner bolt is 33 ft-lb, so it needs to be higher than this, but obviously I don't want a repeat of this problem. Should i put some thread lock on the stud? (i know its often recommended to put thread lock on the helicoil).

 

Not really needed to torque down the stud, maybe hand tight and then some, until it bottoms out.
I personally do not use thread lock on timing stuff, unless stated otherwise in the manual.
M10 should handle 45nm easily, maybe it was over torqued before.