Partially seized 100 HP 4 stroke Yamaha??

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Paull911

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Dec 26, 2006
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My 2001 4 stroke Yamaha 100 HP seems to be partially seized up. I was not operating it when it failed, but the operator says "it just stopped". In checking it out now, with a fully charged battery, the starter will turn the engine, but at about 10% of what it usually does and not enough to start it. I also hear some faint 'metal on metal' sounds as the motor turns over. The operator says he heard no alarms for the overheat or low oil sensors prior to the engine failing. Is it possible for such an engine to "partially" seize up and have its turning over significantly restricted? Any other ideas or advice?
 
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robert graham

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Apr 16, 2009
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Re: Partially seized 100 HP 4 stroke Yamaha??

Remove cowling and flywheel cover to inspect flywheel/starter area, remove spark plugs and crank over the motor. You could have an electrical component or a nut came loose and stuck under the flywheel on the magnets. Good luck and let us know what you find.
 
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patbalmos

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Aug 2, 2011
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Re: Partially seized 100 HP 4 stroke Yamaha??

Remove your spark plugs and check for water intrusion in one of the cylinders or into the oil if thats not the case run a compression test if you can. You probobly won't be able to with the engine spinning that slowly though. You can also try to turn the flywheel with a wrench and see how it feels. It should feel smooth and not grinding.
 
Ernest T

Ernest T

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Re: Partially seized 100 HP 4 stroke Yamaha??

Ignore.......tried to delete
 
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mommicked

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Re: Partially seized 100 HP 4 stroke Yamaha??

Could it be a broken cam?
 
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99yam40

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Re: Partially seized 100 HP 4 stroke Yamaha??

I have seen lower units locked up causing motor to not turn as it should because the drive shaft is directly tied to power head
 
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Paull911

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Re: Partially seized 100 HP 4 stroke Yamaha?? Problem source discovered.

Re: Partially seized 100 HP 4 stroke Yamaha?? Problem source discovered.

Well, the verdict is in. The problem was a cross threaded lower unit drain screw which had been fully tightened, but since it was cross threaded, it was not a good seal, and over the weeks of this season the lower unit gear grease drained out, causing a couple of the bearings to seize up. When they did they impinged on the movement of the main drive shaft, which impinged on the engine turning over fast enough for it to start. It will run about $1,600 for a rebuilt lower unit (complete) and labor. Thanks to all for your suggestions.
 
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99yam40

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Re: Partially seized 100 HP 4 stroke Yamaha?? Problem source discovered.

Re: Partially seized 100 HP 4 stroke Yamaha?? Problem source discovered.

There are new after market lower units made for some of the Yamaha motors, you would have to look and see what they cost if they make one for your motor.
 
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robert graham

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Re: Partially seized 100 HP 4 stroke Yamaha?? Problem source discovered.

Re: Partially seized 100 HP 4 stroke Yamaha?? Problem source discovered.

Paull911 said:
Well, the verdict is in. The problem was a cross threaded lower unit drain screw which had been fully tightened, but since it was cross threaded, it was not a good seal, and over the weeks of this season the lower unit gear grease drained out, causing a couple of the bearings to seize up. When they did they impinged on the movement of the main drive shaft, which impinged on the engine turning over fast enough for it to start. It will run about $1,600 for a rebuilt lower unit (complete) and labor. Thanks to all for your suggestions.
Click to expand...

Well, I'm glad you found it, but sorry about your $1600 repair bill. A cross-threaded drain screw?
That's a new one for me! Good luck! Hopefully nothing else goes wrong!:(
 
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G-Money

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Messages
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Re: Partially seized 100 HP 4 stroke Yamaha?? Problem source discovered.

Re: Partially seized 100 HP 4 stroke Yamaha?? Problem source discovered.

No kidding! I guess you'd have to work mighty hard to do that...or have someone working on it who doesn't know what they are doing.
 
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