Have others experienced this problem and what solution can you offer?
The starter on my 2004 R1150RT has given me problems for years. Three times it as fallen off or became partially dis-mounted from the engine case causing the starter gear not to properly engage with the fly wheel. The problem is the threads tapped into the engine for 1 of the 2 mounting bolts has become damaged to the extent that it no longer holds the M8-40mm torx head bolt.
I discovered that a longer mounting bolt seems to hold because there are still some good threads deeper in the engine mounting hole. A 45mm bolt will catch a few threads but a 50mm bolt seems to catch more threads. The 50mm bolt bottoms out so this solution requires a couple washers as shims to prevent the bolt from bottoming and not sufficiently clamping the starter on. My concern is finding an M8 x 50mm torx or allen head bolt (even a hex head will work) that is compatible with the aluminum engine from a corrosion and strength standpoint. Can anyone provide a BMW part # for a M8 x 50mm torx, allen, or hex head bolt?
If anyone has used a helicoil for this repair, I would appreciate any feedback you can provide?
My first course of action would be to replace the thread insert. My second option would be to consider M8 stud that is fully inserted and loctited in place. The drawback here is that the starter motor WILL be harder to mount and dismount. My third consideration would be getting an M8 x 50 socket cap bolt and machining the tiniest amount off the end to ensure maximum engagement. There is nothing magical about these bolts they don't have to be amazingly strong. For sure the bolt (any bolt) will be far stronger than the mounting point into which it is going to be threaded!
There are also other 'cowboy' options which I will not get into.
I'm not 100% positive but think stainless steel is not very compatible (from a corrosion standpoint) with aluminum. I think it is better to use a regular steel bolt with some anti-seize compound. I know the original bolt is attracted to a magnet.
From a corrosion standpoint aluminium and ss are incompatible and you must use anti seize! Been in the marine industry for 30 years and can't begin to tell you all the tales of horror with outboard engines that became almost irreparable because of that mix. IIRC, there was either a wave washer or spring washer behind the bolts on the starter motor to keep them from vibrating out. Loctite could work but it needs to be the green kind that is more heat resistant.. My 0.02 cts.... YMMV