I have a 2002 f350 diesel that I had a lot of starter trouble with recently. My truck has 240,000 miles on it and has been very good to me. I am posting this because I completed a successful repair, and FTE has given me so much help, I want to give a little back.
The short story is my starter failed in March 2013, drive gear was failing to engage the flywheel when cold. I replaced it with a rebuilt unit and the same thing happened. I inspected and cleaned all the cables focusing the grounds. No help. Got another starter and worked for a bit but failed again when cold. Went for a third and got crap again. I upgraded to a better starter and it's all good. But..... In this process of swapping out starters, the threads on the upper bolt hole came out on the bolt last time around.
I know there is a lot of issues with bolts loosening and attempted fixes. I discovered the soource of the issue with all this. I measured the depth of the hole for the bolts. It is 33mm deep. The threads are M10 X 1.5mm. We get starter bolts that are 35mm long. Only 30mm are threaded. The flange on the starter is 14mm thick. So, at maximum 16mm of the threads are used. Take into consideration there is a 2 to 3mm relief on the bell housing before threads even start. So I say only about 13mm of threads are used.
I have read people adding a lock washer to keep bolts from loosening up. That will take away another 3mm.
What I did to solve my issue was to utilize all the available threads. I first cleaned up the holes with a M10 X 1.5mm tap, lube with light oil and going slowly and cleaning them up by backing the tap off each half turn. When done with tapping, I sprayed the holes with brake cleaner and compressed air. (Wear eye protection).
I picked up a grade 8 stud. 30mm threaded on one end to go into the bell housing. A 10mm unthreaded space and another 18mm threaded on the other end. Total length was 58mm I put Locktite Red #271 on the long end and ran it into the bell housing. After 24 hours I installed the starter and put a washer and lock washer behind a nut for the top.
For the bottom, I used a 10.9 grade M10 x 1.5mm x 50mm bolt with a thick washer and thick lock washer. No locktite on the lower bolt or upper nut. The lock washer will hold it from loosening. The locktite is used only to keep that stud from moving.
It is a little tricky getting the washers and nut on the top stud, but nothing we can't handle.
I can do chinups on the starter now. I suspect the nut and bolt will not loosen.
I hope this approach helps somone else out there. This utilizes all available threads and keeps away from the trouble of installing a helicoil, which I dreaded.
The one big thing to remember is to make sure all the washers are used each time a starter is changed. Otherwise those bolts will go right through and destroy the aluminum bell housing.
Each washer I used was 3.5mm thick.
By using all the threads, there is less likelyhood the bore will strip.