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Hey, i bought a 2003 rm250 about 6 months ago and i am thinking about putting a top end in it, when i bought it i was told that it had 10 hours on the top end, but there was no proof so i don't know,but as far as i can tell there is nothing wrong with it, it runs good, so would you rebuild the top end just to be safe? Or am i just wasting my money?i am new to 2 strokes so any advice is appreciated.thanks

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Hey, i bought a 2003 rm250 about 6 months ago and i am thinking about putting a top end in it, when i bought it i was told that it had 10 hours on the top end, but there was no proof so i don't know,but as far as i can tell there is nothing wrong with it, it runs good, so would you rebuild the top end just to be safe? Or am i just wasting my money?i am new to 2 strokes so any advice is appreciated.thanks


Pull the pipe off and look at the cylinder. Easy way to tell for a quick look, doesn't tell the everything but it sure beats pulling the jug off. If it was 10 hours, the gaskets should look new and have some flex in the corners where they are exposed.
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Hard to say that's scarring because each picture looks different with the streaks. Might just be the way the fuel is being moved around. However if he did rebuild the top end he didn't clean. Check compression, and if all is well run it. What makes you want to pull it apart?

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Hard to say that's scarring because each picture looks different with the streaks. Might just be the way the fuel is being moved around. However if he did rebuild the top end he didn't clean. Check compression, and if all is well run it. What makes you want to pull it apart?

not knowing when it was rebuilt, because if it blows up that's a whole lot more money than a piston

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Then spend 100 dollars for a piston and gasket and change it out. Then you can answer your question. If your not feeling vibrations and no scoring on the cylinder and compression is good, really no reason to continue unless you know there is a lot of hours on the cylinder.

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21 minutes ago, Wcm250 said:

Hard to say that's scarring because each picture looks different with the streaks. Might just be the way the fuel is being moved around. However if he did rebuild the top end he didn't clean. Check compression, and if all is well run it. What makes you want to pull it apart?

He answered your question right there. 

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9 minutes ago, mixgashaulbass said:


i thought compression only had to do with ring wear and not piston wear, is that not true?

It does. Generally you do one( sometimes) two sets of rings per piston.So chances if you have low compression, 120psi or lower then do a new top end. Simple as that. Do a compression test and stop wasting everyones time. 

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i thought compression only had to do with ring wear and not piston wear, is that not true?

Ring wear and piston wear both play a part in compression loss. But the rings are the biggest factor when it comes to compression. As they wear down they lose their edge and allow blow by gases witch in turn lower your compression.
As for the piston wear you'll get a piston slapping noise before it really affects the compression. The piston will wear mostly on the front and rear and allow the piston to shift ever so slightly and allow it to knock or slap against the cylinder walls. But with this slapping or knocking you can still have good compression if your rings are in good shape.

So in short if your pistons wear is In spec just buy new rings to bring your compression back up. If you have any spefic questions I'll be more than happy to help.

I rode a it 200 with a worn piston and new rings for 2 years before I rebuilt it.
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It does. Generally you do one( sometimes) two sets of rings per piston.So chances if you have low compression, 120psi or lower then do a new top end. Simple as that. Do a compression test and stop wasting everyones time. 

That doesn't really answer my question, i read numerous posts about people having good compression and rebuilding it anyway and finding cracks in the old piston, so, since i have no clue how many hours are on it should i just rebuild it?

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If it was me I would test the compression with a tester and if it's over like 115ish 125ish psi I would run it and rebuild it later.

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Ring wear and piston wear both play a part in compression loss. But the rings are the biggest factor when it comes to compression. As they wear down they lose their edge and allow blow by gases witch in turn lower your compression.
As for the piston wear you'll get a piston slapping noise before it really affects the compression. The piston will wear mostly on the front and rear and allow the piston to shift ever so slightly and allow it to knock or slap against the cylinder walls. But with this slapping or knocking you can still have good compression if your rings are in good shape.

So in short if your pistons wear is In spec just buy new rings to bring your compression back up. If you have any spefic questions I'll be more than happy to help.

I rode a it 200 with a worn piston and new rings for 2 years before I rebuilt it.

does piston slap usually happen when engine breaking? (even though your not supposed to)

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Piston slapping or knocking should only happen if your pistons is worn out of spec. When engine breaking you should have a smooth feeling other than the engine breaking like normal. If your hearing a hard knocking noise when under load or engine breaking I would suspect the piston is worn or the cylinder is worn out of spec

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If the bike runs fine and isn't making loud knocking noises you are worrying about nothing.

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If it runs nice and strong, has good compression why put up the money to rebuild it? I would buy the kit and have it on hand for when it decides to take a shit. It is very simple. However if you have OCD like i do and it eats at you then why not go ahead and do it.

Archangel53

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There is only one way to know if it's time:

Pull piston and rings, and measure the factory run-out spec for wear.

Everything else is guessing.

You cannot determine wear by looking, only damage.

You can have ZERO damage and still have a worn out piston and rings....

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