Just rebuilt top end and...

[1998RM250]

Hey guys My 07' RM 250 felt weak in the kicker so I pulled to top end off. The piston looked fine, so I ordered a new set of rings and put it all back togather today. It still feels like it doesnt even have the compression of my old 98' RM 250, and doesnt seem to be running much better. I also cleaned the powervalve and checked the reeds while it was apart, I just dont understand whats up? Is it possible I needed a new piston as well?

 

[whenfoxforks-ruled]

You can not look at parts and declare them good to go. A feeler gauge to check the skirt clearance. An outside micrometer could measure the od of the piston also. A bore gauge will accurately check for out of round and id. Place the rings in squarely and measure the end gap, check a few spots. The things to look at, ports chamfered, bearing cages with a magnifier, abnormal wear patterns in the bore, scoring, and the posters on the wall. Yes, a loose fitting piston and bye bye horsepower, and a lot shorter life. Vintage Bob

 

[1998RM250]

I had the cylinder checked out by the shop and they said it looked okay...
Right now I'm thinking I should have replaced the piston too, thanks for the
advice.

 

[whenfoxforks-ruled]

Get a second opinion? Vintage Bob

 

[1998RM250]

I might just take it all apart again and replace the piston as well, it only took me like an hour or less to tear it down. I thought replacing the rings would fix the compression issue, but I guess maybe the piston is worn.

 

[julien_d]

A compression test would be a good place to start.

 

[whenfoxforks-ruled]

It may be your bore is worn/not round? Vintage Bob

 

[rmc_olderthandirt]

Did you hone the cylinder so that the new rings would seal?

What was the end gap on the new rings?

Rod