Most of us are maybe a little too familiar with the fact that the lower oil filter cover bolt tends to strip the threads on either the bolt or the case, or both. As many of us also know, the reason for this is that Yamaha decided to put a drain passage for the oil filter well in the bike, and have the oil run through the threads of this bolt. The metallic debris that the filter keeps out of the engine internals settles in the drain hole on top of the bolt threads between services, and ends up being ground through the threads and running out through this hole, doing unpreventable damage on the way out. Unless you clean the threads thoroughly, you end up with metal chips chewing on them again on the way back together. The drain hole is just inside the filter cover, next to the oil feed hole from the pump (arrow below) The passage intersects the threads here (arrow) To put a stop to this silliness, I took a a #15 drill (.180") and ran into, but not through, the drain passage. If you don't have a number drill set, and most don't, use an 11/64" (0.172") instead. I drilled to a depth of about .170-.200". Use care. The drain passage is about .120", so the drill will want to bite and dig. Then, I inserted a 3/16" steel bearing ball (.187") into the hole, and drove it in until the ball was roughly flush with the top of the hole. I then staked over the hole with a center punch to add insurance against the ball backing out. I did this with the right engine cover off during a water pump rebuild. It could be done with the cover in place, but you would want to take steps to prevent chips from getting into the oil feed hole next to the drain or in the holes below the filter well, and of course, to avoid dropping the ball bearing into the feed hole in the well. BTW, loose balls like this are readily available at any decent bicycle shop. In drilling the hole, there should not be any real problem created if the passage were to be drilled though entirely, because the ball cannot move down into the bore farther than the bolt. But it makes a better job of it when the ball has a step to stop against. A piece of tubing over the drill can be used to stop it from going deeper than you want. If doing the mod in place, cover the feed hole and the oil passage next to the threaded hole on the cover flange with tape after cleaning the surface well enough for it to stick. Plug the threaded hole with a greased Q-tip to stop the chips from falling through the hole while you drill. Clean out what you can while the swab is still in place, then unscrew the swab. Once this is done, the lower filter cover bolt should behave as does any other 6mm bolt. Note: The diameter of the drain hole starts at 3mm (≊ .120"). I did not try tapping the ball into place without counter boring the hole, but it may work. This mod has also been done with a threaded plug, but that seems way more complicated than necessary.