I have a 2001 commander party cat with a 502 DPX in it. I had it out on the water today and it started to miss slightly and stutter at approx. 60 mph. I slowed it down to 40 mph and then down to 20 mph when it stalled suddenly. I went to start it again and it will not turn over( sounded like a bad bendex in the starter) Got off the lake and got home, pulled the starter and bench tested it and it seemed fine. Now I am stumped as to what it could be. Any thoughts or ideas would be a great help.

Pull your plugs and turn the engine over to check for water in the cylinders. I would suspect bad exhaust / risers at that age.

I pulled the plugs and they were a bit wet but I still cannot spin the motor over( by grabbing the belts) I was thinking of pulling the cooling water pump off of the crank pully to try and rotate it. Thanks for another option btw as everyone else seems to think its a spun bearing. It had good oil pressure and was running cool when it happened.Motr has just over 400 hrs on it which I thought was low but am now starting to wonder.

With the plugs out spin the engine over a bump at a time and see if water comes out of the plug holes . It sounds hydrauliced to me. Are you sure something did'nt freeze and crack ????? If you boat in fresh water i would'nt think risers would be a concern . Pull your dipstick and oil fill cap to check for water in the oil . If you see a light brown foamy substance that is a pretty good indicator of water where it does not belong . Good luck , i hope it's just something minor like a bad headgasket !!!

Well, if you can't spin it with a ratchet or breaker bar on the crank bolt you may have a bad bearing but I would try that first since the starter is off.

How does the water pump come off of the crank pulley?

Volvo uses a bracket that mounts the waterpump in front of the crank, makes changing the impeller a 3-4 bolt snap.Randy

remove the oil filter and open it up and look for shavings..if all checkes out good then your bearings in the intermediate housing took a chit..bad design and will go bad in a hurry if you dont at leaste put grease in it every season..

need an extended wobble headed 5/16th's allen.
my bet is rust in the cylinders(not all but a few) have locked it up alittle.

i agree with THE DEED,put the startes back on,pull the plugs,ang bump the starter,while looking to see if water comes out of the plug holes,if you don,t have a starter button,get someone to bump the starter so you can look closely while the engine is bumped.