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Is this forged piston slap too excessive? Yamaha Phazer 1989

535 Views 1 Reply 1 Participant Last post by  yamadogger01
Hello, as I'm constantly swaying between thinking "this is fine" and "this is not fine" regarding the noise my newly rebuilt engine is making. I thought I would come here to ask more knowledgeable people who might have experienced and run an engine like this before.

I've ran the sled for about 170km so far, runs great, makes good power, easy to start, about 7.7 bar or 110psi on both cylinders, no noise noticeable when I'm actually riding and it gets better at idle once the engine gets properly warmed up.

Before I put the engine together I measured with a feeler gauge the ring gap to be about 0,31mm/0.0122" when pushed down about 3cm into a cylinder from above. Continuing with the feeler gauge to measure the piston-cylinder clearance, 0.12mm/0.0047" started pinching above the wrist pin hole and 0.10mm/0.00394" started pinching at the skirt when I pushed the feeler gauge down from above.

The old pistons got no noticeable wear or marks and they were stock standard sized pistons. So I bought Wisecos of the same size to replace them. In the end of my attached video you can see how much play the pistons got in the cylinders.

So do I need to worry or nah? Thanks for any and all replies.

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I got too curious to see inside the engine so I removed the exhaust manifold to have a little peek. Cylinder walls seem to be getting some extra wear due to the piston slapping but it doesn't appear to be anything too excessive. Any opinions on this?

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