OT: Yamaha outboard engine blew up

The most common reason for this is connecting rod big end bearing failure. From one of the pictures, you could maybe see signs of bearing halves getting overlapped. It can only happen if the bearings are REALLY worn, or if a rod bolt let go.

If there was a blockage in the oil passage or the engine lost oil pressure for some reason, the bearing would run dry and quickly melt/weld itself onto the crank. That's my best guess.

This engine is beyond repair of course, but if you are interested to learn more, see how much oil is left in it and if the oil pump drive got broken or something, that would cause oil starvation.

The reason, I am asking, is to cover up my ass ;) My friends father in law's boat, me driving it with my friend's and my kids. "Did nothing wrong", 10 minutes from the start, normal cruising, BOOM. The engine had been serviced recently and not driven much before this. The cylinders are placed vertically and the No. 1 (the one that blew up) is the topmost. If the reason is oil starvation, that might clear up my conscience. Maybe the "service" done recently went bad.

The reason, I am asking, is to cover up my ass ;) My friends father in law's boat, me driving it with my friend's and my kids. "Did nothing wrong", 10 minutes from the start, normal cruising, BOOM. The engine had been serviced recently and not driven much before this. The cylinders are placed vertically and the No. 1 (the one that blew up) is the topmost. If the reason is oil starvation, that might clear up my conscience. Maybe the "service" done recently went bad.

What Jan said, check the oil level, the engine should have a dipstick just like a car engine. Surprised the rod snapped, would think the engine just would have stopped from the seized bearing..

J.

I am a bit surprised that these engines do not have any warning system for low oil pressure for instance. No warning lights, no buzzers. Should at least IMO cut the power off if oil pressure disappears. Or do they have some sort of system and it just now did not work or the pressure was there but this one bearing was blocked?

Perhaps the oil was displaced with water or gasoline.

The stuff that came out (not much did) looked, felt and smelled like normal motor oil.

Did you actually drain the engine to check the amount? Not sure about Yamaha, but these thing are constructed more or less alike,there should be a drain plug on the outside of the engine cover about 1/3 of the way down towards the propeller.

If it was a modern 4-stroke you would have both visual and a audible alarms for low oil level/pressure.

The last one I dealt with was a Suzuki 50Hp 4-stroke belonging to my father. Brand new, came with the original multi function instrument, it even warned you about the first oil change after some 15 hours(?) of running(complete waste of money, the oil looked and smelled like it just came out of a can).

Not sure about the prices in Finland, the 50Hp Suzuki is now priced at

J.

No. We did not have time or place to drain the oil. But I assumed that it would have leaked a bit more out of that hole in the crank case.

I think it was a 90's Yamaha 50 hp 4-stroke 4-cylinder. Not exactly new, but not old either?

Later model of that