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PW50 Engine Help

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I have been looking at my sons PW50 and i think the engine is on its way out. My son dumped it under the water completely and it sucked a ton of water into it. I drained the case oil and pulled the plug and gradually got it all cleaned out. I rode the bike for the rest of the summer.

It now seems to be rattling pretty good. I thought maybe the exhaust shield but it is not the problem. I did a compression test and it is around 80 psi.

What do you think ?

Piston and rings ? Connecting rod bearing ? What else should a guy replace ? Is it hard to split the case on that little engine ?

Thanks

SB

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When my kid raced PW50, that thing rattled like hell. I took it up to a yamaha shop all freaked out( had a race that day) Guy said dont worry about it. You need a new top end but it wont blow your ok. I would of had them do it but as usual it was a dealer shop and it would take a week+.

That was like 4 yrs ago and the bike finished the series with no problems on a rattling piston. If at that time, I had time and money I would of had it changed, today I would do it myself.

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I took it apart and the bottom is in great shape, no slop what so ever. The top end was a little worn. I'll get a piston and rings and get it put back together. The cylinder looks good as well a little sanding action.

Can anyone give me the ring gap specs as well as head bolt torque specs. Any other specs i might be forgetting.

What is everyone using to hone that little cylinder, my large hone is to big. Brake cylinder hone ?

Thanks

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I took it apart and the bottom is in great shape, no slop what so ever. The top end was a little worn. I'll get a piston and rings and get it put back together. The cylinder looks good as well a little sanding action.

Can anyone give me the ring gap specs as well as head bolt torque specs. Any other specs i might be forgetting.

What is everyone using to hone that little cylinder, my large hone is to big. Brake cylinder hone ?

Thanks

Ring end gap / .006-.014 Head torque/ 7.2 ft ib, when I rebuild my little brothers bike I had the same problem with my hone being to big for the cylinder. I brought it to the local yamaha dealer and got it done for only $5.

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Thanks for the end gap specs. I used a brake cylinder hone with 240 grit stones and it worked perfect.

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One other quick thing. Is there a top and bottom ring or are they both the same on that engine. One ring looks narrower. I don't have a manual for it.

Cheers

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One other quick thing. Is there a top and bottom ring or are they both the same on that engine. One ring looks narrower. I don't have a manual for it.

Cheers

There should be a all black ring and one with a silver outer edge. The silver one is the top ring and the all black is the bottom. Also make sure the arrow on the piston is facing down toward the exaust.

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I found a manual online. There is no mention of two different rings. The rings i took out were more or less identical.

When I rebuild my brothers pw50 the rings did look similar but when I looked closer I noticed one had a silver outer edge. So I callled the company I ordered from and was informed the silver was the top ring and all black was the bottom. What brand piston and rings did you get?

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