Major Problem/Timing Chain Tensioner Threads Stripped

[bmwvuk61]

Hello, thanks for letting me join this forum. I've been a BMW owner for over 35 years.
Here's my story. I've got a 2004 M3 6MT convertible with 112,000 miles on it. I've never really had any major issues in the 12 years I've owned her until about a month ago. I was driving on the interstate when I looked in my rearview mirror and saw smoke coming from my car. I pulled over and confirmed that oil was hitting the exhaust manifold but on the side of the road, it was difficult to see where it was coming from. I had her towed home and discovered that the timing chain tensioner was loose and I was able to turn it by hand. I removed the existing one and inspected the threads both on the tensioner itself as well as the threads on the head. Since the car had 112,000 miles on it, I ordered a new tensioner and washer from ECS and attempted to install it. It started threading fine and once it got to the point of meeting resistance, I got my torque wrench out and torqued it to the recommended 52 ft lbs., hearing and feeling the wrench click.
I looked at the actual tensioner and saw that there were still about 3/4" of threads sticking out which obviously wasn't correct. I even tried to reinstall the old tensioner with the same issue. I have been working on my own cars for over 30 years and can't figure out how I cross threaded the new tensioner. I'm wondering if the previous owner(s) might have had some kind of issue as timing chain tensioners just don't arbitrarily just loosen up, especially after owning the car for 12 years.
I had it towed to a local independent BMW shop and they told me that some of the threads (about 2 rows in) were stripped and that they were not equipped to make the repair.
I've reached out to a few other shops in the area that my shop recommended and have gotten mixed opinions. Because there is absolutely no room down there, it's nearly impossible to get a tap to rethread the head. Other than pulling the head and putting a used head on, is there any alternative that anyone can suggest? (please don't suggest the part the car out, it's not an option)
I'm at a loss here.

[Cubieman]

Anything can be fixed, but unfortunately if there was some clever solution to save the threads your likely going to need to pull the head just to avoid metal shavings in your motor.

If the original threads are gone, I suppose a machine shop could theoretically make some kind of insert to maintain the same size threads.

But realistically, if the threads are gone you are probably looking a getting a different head installed.


Edit: If your tensioner stops 3/4" the way in, maybe just a few threads are messed up, compared to fully stripped threads.

If thats the case, and you find the right mechanic, maybe they could get away with removing the timing chain, sprockets etc., then remove the burr or whatever is causing the issue while catching the metal debris.

[sapote]

I don't see the damaged threads in the hole, but there is an object pointed by the red line. Also it seems the AL washer is still hanging at the hole. The threads on the tensioners is a distance from the washer so the hole doesn't have threads until 5mm or deeper into the hole is normal. show us the pic of the damaged threads.

[jayjaya29]

That "object" is the oil feed hole for the tensioner.

[sapote]

That "object" is the oil feed hole for the tensioner.

I know the oil feed hole but the photo seems to show a protruding object haha!

I can't tell any damaged threads, but it's hard to believe the tensioner can hold the torque at 52 ft-lbs on 2 or 3 bad threads, as all threads deeper than the feed hole seem to be in perfect shape. So there are plenty of good threads in the hole and no need to get the engine or head off the car to repair.

If it were me, and after verify the couple damaged start threads, I would stuff the hole with paper towel, then use a file or angle pick to clean or delete the bad threads, clean up the debris with cotton swap wet with oil or grease, then try to thread the dumb tensioner (remove the plunger and spring) into the hole for a trail run first.