blown powerhead?

[petros]

1999 200 merc saltwater series carburated.Oil injection removed premixed 50:1 pennzoil synthetic with fresh gas.Took the boat out today after raising motor 1 hole ran perfect.Gained over 2 mph at cruise.Back at the dock sprayed i can of seafoam in the carbs let it sit 15 minutes started it up lots of smoke brought it up to 5600 rpm for maybe 30 seconds ran perfect.Throttled down to 4300 cruising for about a minute motor starts vibrating knocking loses rpm and shuts down.Turn the key and nothing felt like it was seized.Couple more turns of the key and fires up runs perfect for 30 secs vibrates loses rpm kmnocks and shuts down.same thing turn the key and nothing just a click.Wait a minute and she fires right up.Bring the boat home hook it up to the muffs runs fine.No knocking.Doing a compression test tomorrow.What do you think???

[roadkill636]

was it still getting good water psi after raising the height?
gas and oil was mixed correctly?

[Specialized P4-12]

not supposed to run full synthetic in a steel sleeve motor.. if thats what ur running.. dont think thats the problem but not supposed to ... sounds like a fuel issue... check ur fuel pump might be time for a rebuild...

[Specialized P4-12]

if it was blown u wouldnt be asking.. u would know.. as long as it isnt rapping u should be ok.. rapping is very very bad.. and you should not start or run the engine cuz its only going be worse if its rapping...

[roadkill636]

what does sea foam in the carbs do? I thought it went into the spark plug hole then sat there a while and worked the rings,,,,

[Specialized P4-12]

yeah i dont know about that one either.. i usually add it to my gas.. but i guess thats another way to clean things out..

[Specialized P4-12]

shouldnt have to do it on a 99 anyway.. even less if it was oil infected.

[flabum1017]

Everything running ok until you raised it one hole....... sounds like the one hole was too high, possible overheat and stuck a piston. Compression may not tell the whole story, pull the heads and look for aluminum transfer.

[gotboostedvr6]

sorry man it looks like you overheated it

[roadkill636]

you may have raised the engine 1 hole,1-1/4" with the added speed the water line on the lower unit may have dropped 2"??????

[150aintenuff]

if you had straight sea foam in the carbs it may have washed the oil film off the berrings and rings causing a "cold Seize" it doesnt sound like an over heat to me but a loss of oil issue... the seafoam will displace the oil film as it transfers through the engine... i suspect this is what caused your issues and you may have also had some detonation due to fouled and misfiring plugs if yu ran it hard before it truley cleaned out..

[John Richied]

Seafoam is also a lubricant so I doubt the engine is seized.
I think what has happened is your ole 1999 has not been decarbed for a while, and you just fouled your spark plugs.

Try removing all the spark plugs; spin the motor over with the plugs out.
If it sounds fine… not metal sound, install new spark plugs and LET IT EAT!
Also I believe what you did was used the Seafoam spary and shocked your engine… You are better off buying the Seafoam in a can and adding it to your fuel as a maintenance dose every now and then.
This will keep the carbon from building up over time.
<O</O
Best of luck to you.

[petros]

water temp didn't go over 150 degrees and pressure was between 15-20 psi.Hope it is the spark plugs but i doubt it.Really felt like it was seizing up.

[petros]

Did the compression test and piston #2 is shot.I had the oil injection removed to prevent this but no luck.The cylinder walls look good but the piston is gone.I have a parts motor of the same year and HP and i am going to try to get the motor running again.This is my first time doing this so i might have some questions along the way.I removed the cylinder head and connecting rod /piston off the parts motor and they look good.

[petros]

cylinder wall and head