My starboard 454 mag with unknown hours locked up while running 4000 rpm.Pulled the Seawater pump,looks good. Of course I'll pull the pan and check the pump but it seems it overheated and had oil? Seems unlikely a plastic bag or something wrapped around the outdrive because SW pump is alive. I have spun bearings before but the motor will still run. Any ideas before I put the new Mtr in and possibly toast it. No alarms and it happened in about 15 secs so I didn't get to watch the gauges. But water press had been running 30 psi at wide open. If my oil pump didn't die I'll be stumped. Any ideas? Don't the rings get oil from the crank slinging oil?Plugs look great not fuel washed not lean.HELP!If a head gasket blew and put a little water in a cyl could that do it?I took the plugs out and it is locked tight!

could be a broken crank! just my 2cents

Outdrive locked up?

Drive or mains.

mtr is for SURE locked,all the plugs out won't budge. I hope it's oil related but will mains cause a running 4000rpm mtr to stop?

i broke a drive and locked the motor, pull the drive and make sure it is the motor.

I agree.....this should be step #1

This Same Thing Happen To Me Last Week On 1 Of My 454's Ho. Was Running Great Then Just Locked Up Without Any Warning At All. Bidge Full Of Oil But No Holes Or Signs Of Leaks In Motor When Pulled. Can't Figure Out Why. Pulled All Plugs Motor Locked Up Solid. I Just Heard A Rumor That Doesn't Make Much Sense To Me. That Champion Spark Plugs Has A Croos Reference In There Books For A Certain Plug Size But There Was A Recall That Merc Dealers Are Suppose To Know About That These Plugs Are Causing 454's To Blow. Just A Rumor At This Time I Quess No Hard Facts Yet.

step 1

pull valve covers and plugs,check for dropped valve or possibly a cylinder full of water.