Fixing a mistake: bad threads for vanos mounting bolt on aluminum head :(

[ATB88]

Need some serious help and advice. Went in to do my routine valve adjustment, which went great, and while I was in there noticed that the seal between the vanos unit and the cylinder head was leaking. Cleaned it up, and replaced the seal. When I was re-fastening the VANOS unit to the head, I found that the leftmost bolt (which I've highlighted in this diagram https://www.realoem.com/bmw/enUS/sho...diagId=11_2994) was not torquing properly into the threads on the head like the others did.

Flash back to 6 years ago when I bought and did the original Beisan VANOS bulletproof work on this car, I was still very amateur and a little clumsy in doing this kind of work, and I now remember that I accidentally overtorqued that bolt last time, and my solution last time was to hope for the best that it wasn't going to leak. I'd totally forgotten about it. SMGDH.

Quite embarrassing, but here we are. What should I do to fix this? What's the best way to verify conclusively that I ruined the bolt threads in the head, and what's the best way for me to repair them if so? Is it possible to repair them in a way that will allow me to continue to use the original size bolt? I know that time serts and helicoils exist.. is there enough access to properly install that kind of fix without taking the head off? Miserable about this and hope it isn't too difficult to fix properly :/

[lemoose]

ooooof I ruined the exact same thread on my car years ago. George Hill ended up having to remove the entire front end to helicoil/timesert it (don't remember what we went with).

[George Hill]

lemoose repair was different than yours, his had a broken bolt IIRC.

For your scenario I've done this many times with a Timesert.

[heinzboehmer]

+1 to timesert

https://nam3forum.com/forums/forum/main-forum/member-build-journals/13854-heinzboehmer-s-2002-topaz-6mt-coupe?p=185407#post185407

[cobra]

What I've done sometimes in the past is if the hole is threaded deeper than the bolt, you can get a slightly longer bolt and it will grab those undamaged threads deepest in the hole. I doubt BMW drilled these deeper than they needed to, but it can happen.

Helicoil or timesert is the proper way to do it. Very easy. The hardest part is just getting a tool in there and making sure it's going in straight. It must go in in perpendicular.

[bmwfnatic]

Did this about a week or 2 ago on a customers engine.
Previous mechanic cut an aftermarket bolt to size with an angle grinder and ruined most of the threads, found it cross threaded...


Using an actual HELICOIL brand kit, not some China garbage as you can only do it right once.
I opted not to go for a TimeSert because the hole is recessed and it would prove difficult to use their large headed tool to create a bevel for it to seat, original dowel can be retained this way too.


Drilled out the remainder of the orignal threads, make sure you are drilling exactly straight, use a drill guide if you feel you might require one.


Slowly run the included tap all the way through, using cutting oil and the 2 turns forward 1 turn back method.
Blow out the hole and carefully clean it (brake cleaner, compressed air).


Insert installed with the included tool and some Loctite 270 (high strength), let it cure for an hour or so.


Tested out the repair by mocking up the VANOS unit and taking it to 10nm with a brand new BMW bolt, perfect.

[ac427]

Nice work 👍

[ATB88]

Thanks, especially to heinzboehmer and bmwfnatic for the writeups! Makes me feel a lot better, although drilling out the original threads on my head still makes me sad Not that can really be avoided at this point (or can it? is there a chance that a thread chaser can still save me here?)

I assume that both of you were able to do all of the work and get the tools where they need to be with the head and entire front end in place (other than, say, the fan shroud and fan clutch)?

On first pass the helicoil route seems easier due to the countersink on the timesert requiring a resized dowel. Is there any reason I should try and go the extra mile to do the timesert over the helicoil? I've gotten the impression that overall a timesert is a "more correct" solution to this type of problem but I feel like I want to do the thing that I'm least likely to mess up as long as the repair will hold indefinitely. Is one more or less reliable than another in this particular situation? Would be happy to hear pros and cons of either approach, although I understand it might come down to personal preference.

[Slideways]

Thanks, especially to heinzboehmer and bmwfnatic for the writeups! Makes me feel a lot better, although drilling out the original threads on my head still makes me sad Not that can really be avoided at this point (or can it? is there a chance that a thread chaser can still save me here?)

I assume that both of you were able to do all of the work and get the tools where they need to be with the head and entire front end in place (other than, say, the fan shroud and fan clutch)?

On first pass the helicoil route seems easier due to the countersink on the timesert requiring a resized dowel. Is there any reason I should try and go the extra mile to do the timesert over the helicoil? I've gotten the impression that overall a timesert is a "more correct" solution to this type of problem but I feel like I want to do the thing that I'm least likely to mess up as long as the repair will hold indefinitely. Is one more or less reliable than another in this particular situation? Would be happy to hear pros and cons of either approach, although I understand it might come down to personal preference.

Due to the bore for the dowel, probably easier to helicoil this one. With red loctite on the helicoil, it should be a permanent fix. To get a straight shot at that lower bolt, the rad, condenser and front core support probably have to be loosened and move around to gain access. The procedure to gain access is similar to extracting the rocker shaft on the exhaust side.

[heinzboehmer]

I assume that both of you were able to do all of the work and get the tools where they need to be with the head and entire front end in place (other than, say, the fan shroud and fan clutch)?

You should be able to get a right angle drill in with just the fan and shroud removed. I ended up just doing it all by hand (even the drilling). It's soft aluminum and half the threads were already chewed up, so it was pretty easy. I used a drill and tap guide to make sure everything was square.

[George Hill]

You can likely drill it by hand as Heinz said its pretty soft already. Get a set of tap drivers and you pan put it on a small T handle ratchet.

IMO Helicoils are not a permanent repair on a bolt that needs to be removed, I would consider it only in a pinch or on a bolt that I didn't plan on ever having to service. YMMV I'm not interested in getting into a debate about which is better but thats my opinion lol.

You should be able to use the vanos as a drill guide.