Engine seized or gearbox/Lower unit seized ??

Was running at 5000rpm and as started to throttle back engine suddenly sounded very loud( as if exaust had droped off)immediately shut to idle and engine died would not restart and seemed very tight.There were no warning signs ie loss of power etc or horn or lights. After 2 hr struggle through 30mph wind and seas on trolling motor got back to mooring.Engine still tight so pulled plugs alll in perfect condition color good no bits etc .At no time did engine smell hot or even feel over hot .Was wondering if could be lower unit input shaft bearing seized? ps noticed prop spinning extremely freely in tide when in neutral.When get down again sat will check compresion etc just wondering if any thoughts . http://www.bassboatcentral.com/smileys/crying.gif

What do you mean by engine seems 'tight'? I'm not familiar with your motor, but on mine you can grab the bolt on top of the flywheel with a wrench and turn it. Should tell you if it's locked up (pull your kill switch first). I'd definitely pull some fluid out of the gearcase and see if that gives any hints. If you've got milk and metal, then that's probably the deal. Although, when I blew my lower unit last year, it would start just fine in neutral....just wouldn't go anywhere.

I can turn engine if i use both hands on side of flywheel but is very hard to turn even with plugs removed.When ever ive had engines seize before they have all ways stopped dead and and been locked up also all ways had deposits on plugs.Have not had chance to do proper checks yet was just living in hope that may not need engine rebuild ps it only done 80hrs from new.

I wouldn't get too worried just yet. You need to check your lower unit fluid first. Also get a compression gauge on there and see what's happening.

Take a deep breath, click your heals three times, and hopefully champman, seahorse, or one of those guys will stop by and give you some more things to check.

The motor will have some resistance to it when spinning by hand. As you are also spinning the water pump. A quick check would be to shift into gear and see if the prop spins freely and then binds. Then pull the drain plug and see what comes out.

Sounds like the L.U. may be the problem. Just remove the drain plugs and evaluate what comes out. Metal chunks and bad smelling oil usually denote a gearcase problem. Look closely around the area of the pinion bearing. This will be just in front of the water intake hole/holes. (depending on which style you have) Check for case swelling at this point.

its what mine did when the lu went out the 2nd time. wont turn over or anything. however mine was obvious the lu was going at the time.

Thanks everyone for your replies have been down too boat and checked compression on all cylinders all at 100psi except number 5 which was only 55psi .Connected computer and had no fault codes stored or hard no over temp etc etc but forgot to check max rpm will do so when i get it home.Pulled head from port side found piece of what looks like piston ring stuck to head it is magnetic which makes me think ring lucky no scoreing or damage to bore or head slight marks in head and exaust port can just be felt with fingernail not measureable though .will no more when i strip engine hoping ring groves not damaged so can just replace rings . I assume this damage happened due to over revin g when i first got it running with defective revcounter when fixed counter found it turning at 6300 rpm.Any thoughts on any of this appreciated please .anything to watch out for when doing rings have rebuilt a coup[le merc black max and a merc straight 6 but never a DI motor ! http://www.bassboatcentral.com/smileys/bows.gif