jleidel

In preparation of doing a timing belt/water pump on my 80', I had a serious and unfortunate issue come up. In trying to remove the belt tensioner mechanism, i stripped one and broke a second bolt.

Has anyone had any success with drilling/tapping these guys?

SharkSkin

Ouch. no direct experience on the 928 with this particular problem, but you want to go with timeserts rather than helicoils IMHO.

This is not for the faint of heart. You may want to remove the radiator to gain clearance and/or rent a right-angle drill. If one of the bolts is the one that goes into the oil drain-back channel from the head, you're going to have an issue with getting chips in the oil passage. Do you have any pics?

The bolt with the drop of oil on it in the pic is the one that gos into the oil drainback.

jleidel

Don't have any pics quite yet, but will grab a few in a few minutes.
Indeed, the bolt that goes to the oil drain is in fact the one that broke. BAD NEWS. The stripped bolt is the one on the top left.

SharkSkin

You might be OK. Soak the broken bolt in PB Blaster or Kroil. If it broke above the surface, you're in luck. grind it flat, center-punch it lightly and start drilling with a left-handed bit. It will probably come out OK, but you'll have to be carefulnot to drill all the way through it. That bolt should be installed with silicone, not threadlocker -- but you never know. If it's broken below the surface, don't center-punch it because it could mushroom and wedge in the hole. Maybe use a small dremel bit to make a dimple on-center then try the LH bit.

jleidel

pictures:

broken bolt from the oil drain side...


tensioner mess:

SharkSkin

It looks like the broken bolt may be broken below the surface. What would be more interesting to see is how the block looks, and is the bolt broken flush, recessed or protruding?

jleidel

The bolt is definitely broken way below the surface. The last ~1/8 inch of the bolt is all thats left as far as i can tell. However, its nearly all the way back in the hole. Its in such a horrible position that I can't get a good enough look at it.

Am I hosed?

Landseer

Enough threads in the hole to use a shorter bolt and leave the broken piece?

jleidel

Probably... still needs to be tapped though...

Landseer

Well, may be a blessing in disguise.

Metal cuttings should be blocked from entering the system.

Landseer

I've had to do several. Hard part is drilling-out the steel bolt. If that doesn't need to be done, you are very lucky.

SharkSkin

I agree with Chris. Rule of thumb is, bolts should engage a length of thread 1-1/2 times the diameter of the thread in steel, 2x in aluminum. Can you show the broken bolt in the tensioner, similar to my pic?

Use a thread chaser on that hole rather than a tap. You may have to grind off the tip of the chaser to get at more of the threads, but quench it in water often and don't let it get hot enough to turn blue. You have to be very careful about bottoming against the piece that's left in there, either with the thread chaser or the bolt because you can snap either one off.

jleidel

I'll see what i can do.

jleidel

SharkSkin [et.al], took your advice and went ahead to remove the entire tensioner assembly. Turns out, the guide for the top right bolt [oil return bolt] is cracked.

ROG100

John,
How far does the crack go?
Is it just the corner of the web that is broken off?
Roger