Re: oil pump drive
Depending what cylinder it is, it could be a leaking crank seal or a crankcase leak. Either could lean it out enough to trash a piston. If the ignition is too far advanced it can trash a piston or more, but it usually picks on one for some odd reason. The other options are breakage from a flawed casting, overrevving, or other fatigue. It could also be carbon build-up in the ring grooves forcing the ring against the cylinder wall too hard.<br /><br />It is also possible that it suffered damage from a prior overheat or some other cause and lost compression on just that cylinder. The other 5 would keep it going, but lack of compression would mean lack of fuel draw to the bad one. Since the lubrication comes with the fuel, it starves for lubrication and that really messes things up in a hurry.<br /><br />Several years ago I had a boy's camp bring me their motor to fix for lacking power. It had no compression in 1 cylinder. I removed the head and found that one cylinder was pretty much toast. "It still ran when we brought it in, just put the head back on." I refused because I knew that if they kept on running it, that cylinder would go completely and leave them stranded. They were really pissed at me, but they would've been a lot madder WHEN it locked-up entirely. It would've been less than an hour for sure. I also refused because it was a 200 on a 150max boat. When I find that a boat is overpowered there are three things I CAN do. Refuse to work on it at all, decomission it, or diagnose a problem but not fix. Making it usable on that boat is not an option. But that's another story.
