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Top end rebuild. Worth it?

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Okay, so I've got this 2003 Rm 125 that runs pretty good, but I've done minor things to it such as buying aftermarket pipe and silencer, change the jetting, and soon I need to replace the fork fluid and seals. But anyway, one thing I have been debating to do is to replace the piston and rings. I bought the bike 6 months ago from a former pro (It's winter in Wisconsin, so I've only had a chance to race it 2 times). He used it as his practice bike. It was in pretty good condition. He only wanted $600 for it, so I had to take the deal. He said that he had a Wiseco Pro-lite piston in it, but he didn't remember how many hours it had been since he replaced it. So here's the question. Do I buy gaskets, take the cylinder apart, take a look, check the compression, and then if its really bad looking just put it back together and ride it until it blows up? Or, do I buy the gaskets and piston all at once and replace it no matter what?

Thanks.

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Be smart and rebuild it or you will spend alot more money in the long run!

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Be smart and rebuild it or you will spend alot more money in the long run!

Ditto.

The rule of thumb when buying a used two-stroke: immediately invest in a new top end. Your wallet will thank you.

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Just do it, as in new piston, wristpin bearings, gaskets, and clean that nasty exhaust valve. When I got my bike I left it alone, and two days later the exhaust skirt broke clean off the piston and ended up costing a lot more than just a top end.:p

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Well, my buddy is bringing his cylinder compression gauge to my house, and we're going to check it out. What is a good psi reading? I've heard it should be about 130-150. Is that right?

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Dude-forget about checking it! Just buy the $129 top-end kit from motosport and put it in. 2 strokes are so cheap and easy to rebuild, so don't take any chances on causing more extensive damage.

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I'd check the compression before i rebuilt the whole thing. You could at least take the engine apart and replace the rings and while its apart check the piston for scoring and damage and such.

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Dude-forget about checking it! Just buy the $129 top-end kit from motosport and put it in. 2 strokes are so cheap and easy to rebuild, so don't take any chances on causing more extensive damage.

I got my wiseco kit from oemcycle and it was only like $96 with everything that i needed for the rebuild!! (i still haven't gotten around to rebuilding it yet though :p )

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I checked the compression, and it read 125 psi, I've heard that that is an okay number. I'm still debating on wether I should replace the piston now, or later this spring/summer when I have a bit more cash laying around.

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I checked the compression, and it read 125 psi, I've heard that that is an okay number. I'm still debating on wether I should replace the piston now, or later this spring/summer when I have a bit more cash laying around.

With only 125psi (not a bad number, but still) i'd probably rebuild it. You could take the piston out and post some pics and see if people think you should rebuild it or put it back in and wait a while.

Just my 2 cents!

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you should really put the new top end on. i bought a used 2 joke and it ran fine so i didnt bother with a new top end. the next thing i new i had the piston skirt break off and had to pretty much buy a new engine. there should be no question about putting a new top end on it.:p

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