74 9.9 johnson locked up

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SMP142

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***(Correction, my motor is a 76, not a 74)

I picked up an old polarkraft last winter that came with a 9.9 johnson that was super clean. i hadn't had the boat out any since i rebuilt the whole thing. I checked over the motor and ran it in the back yard with muffs with a new tank of gas. everything checked out so i took it to the local lake and ran it around for about 30-40 mins. everything ran good but i had to adjust the shifter linkage because it would not stay in nuetral.

anyway.... I ran it in the back yard again with muffs while adjusting the linkage and everythign was fine. I took it out to the lake on saturday and it started fine. started heading out into the lake about 1/3 to 1/2 throttle just kind of puttin' along. it bogged down slightly and died. i figured i forgot to prime the gas tank so i gave it a few pumps and started it up again. took off and about 2 mins later it happed again so i knew somethign was up. the starter would not turn it over, so i took the cover off and there was a little smoke. just smelled hot but nothing burning.

i tried to rotate the flywheel by hand it it wouldnt move, so i turned it backwards to break it loose. it did not take much effort so i know it was not seized up bad. i let it cool down for about an hour and tried to turn it over once. there was obviously no compression.

since i got it home i pulled the plugs and they look fine. the top of the pistons don't seem to have any shavings or pieces in them.

I am assuming my thermostat stuck or my water pump went out. (common on this motor i hear). so is it more likely my head gasket or my rings?

I am going to have to pull it apart regardless but what seems to be more common? I figure if i am going to have it torn apart i should rebuild the whole thing. but if it turns out to just be a head gasket, should i just put in a new set of rings and call it good?

new to outboard rebuilds but done my fair share on other 2 stokes and 4 strokes. i figure its fairly similar.
 
Water pump failures on this engine are no more frequent than on any other engine. However, that being said, these engines sometimes are used in places where most boats and engines will not go!
Also engines of this vintage have typically been passed around from owner to owner and some folks simply will not replace needed service parts until a massive failure occurs.
You have to find out what kind of damage the engine sustained before anyone on here can tell you which way to proceed with a repair.
Since the engine stuck hard enough to lock up it sounds like you will have easily visible damage once you pull the cylinder head. The piston top is not where you will find the damage.
Damage is normally found on the cylinder walls where the skirts of the pistons have gouged them and left metal on them. You should see this after cylinder head removal.
 
yeah, i am afraid to open it up. but i guess it will never get done unless i do so. i think a part of me is hoping it will "magically" fix itself by sitting in the shed lol. i guess i will tear it down this weekend. prob take some pictures of what i find...
 
Here is a link with a lot of good information about your motor. The author has put a lot of detail and pictures to help with repairs.

https://www.leeroysramblings.com/OMC_info/OMCinfo.htm
 
thanks for the link. I have seen 2 of his pages, but i didnt know there was a page area with mulitple topics.
 
***update***

I torn the engine down and both pistons were toast. The cylinder walls were scored deep as well. I waited around for awhile and found a block with pistons online for $60! it was from an evinrude but it fit after i did some match grinding on the upper black collar around the crank. honed the walls and put everything back together.

the cause was the water pump impeller was shredded. however, i think it was because of the housing. i didn't notice a problem until i started putting everything back together. i got a new impeller and installed it. Put the motor in the water tank and got it running after i found a loose ground.

so the motor runs but i wasn't getting any water from the bypass tube (i installed one while it was apart). i shut it off and took the lower unit off again. i took the hose and put it on the intake tube that goes to the powerhead and i get water out of my bypass.

when i looked at the water pump again, the metal interior part of the housing that the impeller glides on got spun around. it normally has an opening where the water can be pushed out and up through the tube. this was imbedded about 180 degrees off from there. so there was no way for water to be pushed out.

so.... i am ordering a new housing and will go from there. this process seems to be one thing after another lol. i want this done so i can fish!!!
 
***another update***

new water pump fixed the problem. took it out and it ran alright. had to run the idle a little rich, but now it runs good. however, since i finished the interior on the boat it won't get up on plane.

so, bought a 1980 25hp evinrude. needs a little work so we'll see how that works out.
 

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