2011 MCS
I always hand start all bolts - you pretty much have to on the MINI anyway as tool access is always limited.

I took the right engine mount out to remove the friction wheel.
I removed the friction wheel to get the new water pump pulley on the new water pump.
I had dropped the engine to get the old water pump out, so being most of the way there it wasn't too much effort to pull the friction wheel.

Feeling pleased with myself, I was buttoning everything up and when I started the 16mm M12-1.5-50 bolt on the engine mount I hadn't realized it had cross threaded until about 1/3 way in when it got very very tight.

Options.
There seems to be a trick where you sacrifice an identical bolt by cutting slots in the end and driving it in. Somehow this "fixes" the thread.
Thread restorers
Can the thread be retapped?
Helicoil

My goal with this car has been to learn how to do things myself. However, the last time I had an issue with a crossed thread it wasn't in a critical place and I didn't bother fixing it. This one is a tad more important.

If I take it to a shop it's going to be an hours labor getting to the mount and an hour to put it all back, but given my amateur status perhaps that's a better option. I'd like your opinions on how to proceed.

The MINI has been demoted to 3rd car and isn't being driven apart from around the corner for its annual MA inspection, so no hurry.

On a different note, I might have avoided all this additional disassembly if I had pried the engine over a bit to get the old water pump out and that may have also helped the pulley issue, but I couldn't make out how this was done in some YT videos, ie what leverage points were used and so being cautious, didn't try it. Perhaps someone can do a write up on that trick with some pictures to help.

cheers
MacMini34

 

More often than not you can use a thread chaser / restorer and get the threads back into reasonable shape. I've had good luck with them in the past - buggered O2 sensor threads, cross threaded wheel lugs, etc. You'll probably have to order one online, most auto parts stores only carry ones for spark plug and O2 sensor threads - That's what I've had to do.
I would hesitate to use the sacrificial bolt method as a proper thread chaser is made from much harder steel.
Chasing it with a tap will be difficult (but not impossible) because the flutes are much narrower and it will want to "walk" into the crossed threads more easily.
Helicoil would be a last resort.

Edit: Use plenty of oil on the chaser to keep it from binding up. I usually just use motor or gear oil

 

Chasing the thread with a tap may be restricted also. Worse yet, if you break the tap it's a horrible repair. Cutting the notch in the bolt is not a bad idea. There is the the possibility that the bolt goes in and tightens up. If it does, I would leave it alone. If it goes to the bottom the bolt , it will still be strong enough to hold the engine mount.
Move along little doggie, your idea is sound.

 

I can't recall, is this a blind hole? I suspect it is not.

If not, then you can access the backside after removing the wheel / liner from the wheel well.

At that point I would attempt to run a well lubricated tap up the back side. If you truly ran the bolt as far down as you believe, then the hole is well and truly F'd up! And trying to repair from the front side takes more than a little skill to get the tap aligned.

Cleaning out a crossed threaded hole in steel, with a steel bolt, does not have a high chance of success.

Worst case you can install a helicoil if the clean out attempt fails. If you do manage to clean out the threads, be very conservative with bolt torque (much lower than spec'd) and use some blue Loctite on the threads.

Be very careful counter boring for the helicoil, drills tend to pull into holes very fast.