For Sure !!!.............Then...Pull plugs & try to crank

Cut the filter open also and look for debris.

Everytime that happens to me it is a dropped valve. The dropped valve also results in a smashed spark plug though and it sounds like all your plugs check out ok. Make sure to compare the plugs closely and look for any that are steam cleaned. Tuliped exhaust valve can suck enough water to break things internally (rods) yet due the loud exhaust make it seem like a silent failure. Of course, removing the drive and cranking is the first order of business. Tomorrow I start the assembly process on my sb engine that lost a valve two weekends ago... you are not alone

BT

mtr is out of boat,plugs out of mtr,it is locked tight. I will tear down soon while building my roller mtr. Every time it breaks it's gonna get faster!That'll show it!

See, there is a silver lining in every cloud!

It sounds as though you have broken a crankshaft my friend. Sorry to hear it.

I had the same problem, running 4500 RPM's motor locked up. Reason for locking up was obvious, ( rod sticking out the side of the pan ) fiding the true cause is another story. It was a fresh rebuilt motor, this sucks !

Ihad the same problem once... starboard motor locked up at about 4500 rpm... no warning ... no alarm.... this is what I found inside.....

The reason for the failure was the remotely mounted oil filter was plumbed backwards.... Here is a picture of the mechanic that did the work......

i still say crank shaft!