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Old 19-12-2015, 17:38   #1
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2hp Yamaha Outboard Dumb Question

I'm rebuilding my tender 2hp Yamaha outboard, and I have a new piston. It has the word "UP" printed on the crown, as well as an arrow.

Sounds good so far, but if I have "UP" reading the right way up, the arrow points down, but if I have the arrow pointing up, then "UP" is upside down.

Yeah, I know I'm dumb, but can someone please tell me which is the right way UP for the piston?

Cheers, Graeme
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Old 19-12-2015, 18:21   #2
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Re: 2hp Yamaha Outboard Dumb Question

How is the original piston placed ? Does this relate to a locator pin in the ring groove to stop the ring gaps catching in an intake port. Have not had my 2hp Yamaha apart yet.
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Old 19-12-2015, 18:44   #3
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Re: 2hp Yamaha Outboard Dumb Question

It's the arrow."Up" is the label for the arrow, not the side of the piston it's on.
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Old 19-12-2015, 19:13   #4
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Re: 2hp Yamaha Outboard Dumb Question

Based on a bit of googling, youtubing and responses on another forum, it seems the arrow points (down) to the exhaust port, and "UP" goes right-way-up at the top. This keeps the ring ends away from the exhaust port.

The interesting thing is that the piston was the other way round when I stripped it down, which might explain the broken ring and piston that got me to this point. I bought this motor in close to new condition, and I believe it had not been stripped down at that point. So maybe this is one of Mr Yamaha's rare goofs.

Cheers, Graeme
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