Engine case bolt - bad threads

Bump. Same thing for me but on an oil filter cover bolt. Mic the bolt and put in a slightly oversized?

If there are still enough good threads in the case you may be able to repair them using a tap. But to me it sounds like the threads are gone so you will have to install a heli coil. If you are unsure/unfamiliar with using a tap the your best bet would be to take the bike to a competent mechanic for the installation of the heli coil. It involves drilling the hole to the correct oversize, cutting new threads, then installing the insert.

The head of the bolt and the size of the threads are different. 9 times out of 10, a bolt with an 8mm head has a thread diameter of 6mm. Then you must consider the thread pitch. Metric threads are sized according to the distance between the peaks of two threads. In your case this will be 6mmX1.0, or 6mm bolt with 1mm distance between two threads, if i am not mistaken.

F'in Suzuki's are the worst, get a heli-coil kit. Comes with the right size drill bit, the existing hole should keep the bit true, keep the heli-coil shielded by the plastic handle so it goes in the case without expanding and binding. I'm sure there's a youtube video somewhere on this.

Sometimes you can clean out the case thread hole real good, run a chase bolt or same size tap through to clean up existing threads and try a new slightly longer bolt to catch some good threads. I have stripped my share of bolts & cases over the years, I hand tighten all 8 mm bolts first, if I feel resistance I stop, take bolt back out & clean up threads with chase bolt and/or lubricant until bolt goes in smoothly.