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Old 13-12-2016, 13:59   #1
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Yamaha 8 HP 2 stroke seizes

2012 Yamaha sat all summer and was seized when tried to start . Removed cowl and starter recoil and unseized with large socket on flywheel. Started right up and ran for 90 minutes in water tank">fresh water tank. After sitting two weeks, seized again, and repeated above and it's running/starting today. Anyone have any ideas about what's causing it to seize after sitting a few weeks. Never had a problem like this with multiple Yamaha outboards, and have to resolve prior to departing Tampa for places south this winter, and Yamaha just says "take to a dealer" Yeah, right!
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Old 13-12-2016, 14:04   #2
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Re: Yamaha 8 HP 2 stroke seizes

Water is getting in somehow, maybe head gasket?
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Old 13-12-2016, 14:41   #3
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Re: Yamaha 8 HP 2 stroke seizes

Seized or just rust bound?

Seizing, in my book, is when the piston starts to weld to the cylinder walls or piston material is coming off the piston crown. Usually due to lack of lubrication, incorrect tuning, wrong heat range on plugs, etc.

If slight rust is issue, not real heat damage, then track down the source of water. You have the plugs installed during storage, yes?

Slight possibility might be the fuel quality, especially if ethanol fuel.

A real seized engine would take some real muscle to break free, and wouldn't do this while sitting still.
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Old 13-12-2016, 15:27   #4
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Re: Yamaha 8 HP 2 stroke seizes

I think it is water from cooling jacket or head getting onto cylinder walls. It freezes when just sitting. If an engine quits suddenly, then I think lack of lubrication or excess heat is the cause.
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Old 14-12-2016, 10:38   #5
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Re: Yamaha 8 HP 2 stroke seizes

Ethanol fuel? It picks up water during storage and enhances rust sticking.
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Old 14-12-2016, 10:56   #6
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Re: Yamaha 8 HP 2 stroke seizes

It's very unlikely this is being caused by the fuel. The potential amount of water in the fuel remaining in the combustion chamber after the engine has been running will be minuscule.

When you break it loose is does it pull through easily or is it still harder than before? And if you stop the motor, then restart it, is it still easy to pull through?
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Old 14-12-2016, 13:07   #7
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Re: Yamaha 8 HP 2 stroke seizes

So my guess is it's the starter string and mechanism getting hung up
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Old 14-12-2016, 13:07   #8
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Re: Yamaha 8 HP 2 stroke seizes

Try taking the pull string starter apart and lube
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Old 14-12-2016, 13:37   #9
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Re: Yamaha 8 HP 2 stroke seizes

I wonder if anyone thought to ask what oil you are mixing in the fuel if ANY!
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Old 14-12-2016, 13:37   #10
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Re: Yamaha 8 HP 2 stroke seizes

Has it been stored outdoors all this time? Could rainwater be entering the engine?
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Old 14-12-2016, 14:58   #11
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Re: Yamaha 8 HP 2 stroke seizes

Worth a look in the bore, how about ordering a new head gasket, when you have it, take the head off and have a look at the bore. If it looks good then have a look in crank case, problems can occur due to main bearing problems or the big end, especially if your outboard ever went for a swim, its worth a look in there, yes this happened to me, all three bearings were shot, the bigend was tricky as its a needle bearing and the crank webs had to be separated and realigned for assembly.
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Old 14-12-2016, 15:47   #12
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Re: Yamaha 8 HP 2 stroke seizes

Are you storing it upright or laid down?

If laid down is the lower unit higher than the power head?
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Old 14-12-2016, 16:41   #13
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Re: Yamaha 8 HP 2 stroke seizes

Nope not any of the above.

Your gasket at the bottom of the power head is leaking salt water through to the "Dry Side" and spraying it onto the lower crankshaft seal housing, which also houses the drive shaft. The housing is corroding and grabbing the shaft.

Prove it by removing the lower unit, I bet you struggle to remove it. When it is out, look for whitish residue near but just below the splines, and a polished area where it rubs on the corrosion.

If you can now leave it for the same amount of time without further seizure, BINGO.

Problem is that if you put too much torque onto the nut at the flywheel, while the lower crankshaft was held, you might have changed the timing of the pistons, so they are not exactly 180 degrees apart from each other.

Let me know what you find please.
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Old 14-12-2016, 18:38   #14
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Re: Yamaha 8 HP 2 stroke seizes

If you'll do a little lookin', you'll find that smaller outboards are outsourced to other manufacturers, usually in mexico. The metals used are soft and the humidity causes rust in the cylinders, hence seizing the rings to the cylinder walls.

Had a Nissan that did the same thing. squatted a few drops of marval mystery oil in the plug hole and pulled the cord a couple times before puttin' the plug back in. two to ten weeks later I just put it back on the dink and gassed her up and it started.

Craftsmanship is a thing of the past.
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Old 14-12-2016, 18:55   #15
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Re: Yamaha 8 HP 2 stroke seizes

Its not seized in the cylinders I don't think. to the OP, if you find I was right, please get in touch to confirm, I think I know what causes this.
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