15HP 2 Stroke Water in Cylinder 1

[Wosat1234]

Hi Guys,

We have a 2004 15 HP 2 stroke motor (15FMH) that was seized after sitting for a couple of weeks.

When the head was removed, we found light corrosion in cylinder 1 (top) and emulsified oil in the spark plug and in the cylinder ports.
The bottom cylinder appears to be fine and looks normal.
The first thought was that there was a blown head gasket, but there appears to be no evidence of blow by or marks where the head gasket seals the cylinders to the head.

It's all a little weird.

Is there is another way where water may be able to enter only the top cylinder on these motors or am I just overthinking a faulty head gasket?

Cheers,
Brett

[TownsendsFJR1300]

I'd check the head closely for corrosion and /or a hairline crack..

[99yam40]

check the exhaust cover plates also for corrosion/holes

[Wosat1234]

Thanks for taking the time to reply guys.
I will just have to work out how to remove the power head to check out the exhaust covers. :-)

Thanks again.

Cheers,
Brett

[TownsendsFJR1300]

Thanks for taking the time to reply guys.
I will just have to work out how to remove the power head to check out the exhaust covers. :-)

Thanks again.

Cheers,
Brett

This engine is probably very similar and you should be able to access the exhaust cover W/O pulling the powerhead:

https://www.boats.net/catalog/yamaha...nder-crankcase


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