I rebuild a lot of Polaris two strokes. The 250s and the 400s. For some reason the rebuilt quads never have the smoothness of sound, the factory ones have. I've tried Namura, WSM, Wiseco and even factory Robin pistons. They always have a louder tone to the engine. It doesn't matter if they are bored, factory bore, even just re-ringed. They sound different. I've tried buying the rubber fin dampeners, did nothing. They just seem noisier. They run fine, Compression is perfect. Some guy told me you have to polish all the parts. I know Polaris doesn't polish anything on the assembly line. They just bolt everything together. My only assumption. All new parts and they all break in together, and now your changing that or its in the exhaust and that makes more noise because you are breaking the seals and reassembling. I have never seen this problem in Kawasaki's or Yamaha's. Just Polaris and it drives me insane. Anybody else have this? Its not just me. I can tell a rebuilt one right away, its nosier, just like mine.
Polaris two stroke rebuilds sound different? Why?
- Thread starter Panzerman
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could it be the balance of the piston crank assembly?
The 400 have a counter balancer. Still I doubt Polaris is balancing anything from the line. A two stroke single cylinder, I would think would have a wide balance range. Even with factory pistons and rings, though , they are louder.
Maybe the act of restoring factory, or greater, compression and combustion force causes them to return to "normal" noise levels. No doubt that by the time these engines get to you for rebuild they are worn out. Maybe what you are comparing is just the sound of a worn out engine to one that's making new-like power.
I'd guess it's piston to wall clearance that sets the "noise level" in this case.
Put another way, quite possibly, the factory ran them tighter, you are not likely to find a shop that is willing to set piston to wall clearance tighter than specification, but it's quite possible the new parts were tighter than the published spec.
In the manufacturing industry, this form of "tribal knowledge" can result in all sorts of problems down the line.
On our G550 aircraft, the flight control actuators leaked like crazy when new. Needed to be overhauled prior to delivery! The reason... The old guy who made them retired. The new guy made them right to spec. Clearly, the old guy knew that tighter was better...
Put another way, quite possibly, the factory ran them tighter, you are not likely to find a shop that is willing to set piston to wall clearance tighter than specification, but it's quite possible the new parts were tighter than the published spec.
In the manufacturing industry, this form of "tribal knowledge" can result in all sorts of problems down the line.
On our G550 aircraft, the flight control actuators leaked like crazy when new. Needed to be overhauled prior to delivery! The reason... The old guy who made them retired. The new guy made them right to spec. Clearly, the old guy knew that tighter was better...
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