Eric:1st Top end rebuild do I have all the info?

[GeoffM24]

While I am fairly handy this all seems to be getting out of hand in compexity.

I have a 99 RM250 that posted a compression PSI of 185.

So after reading that 250s should be in the 235-250 range I decided to rebuild the top end.

Sometimes it seems simple sometimes it seems extremely complex.

OK, tearing down the cylinder and getting the piston and rings off sounds reasonable.

These parts worry me.

1) tearing down the power valves to clean them since there is no Clymer for my bike how do I know how to take it apart and put it back together?

2) Honing the cylinder??? I saw where I can get a tool for $31 but this seems like a tough machining process. Do ALL cylinders need this?

3) Piston size. I ASSUMED I'd need std. but you are saying there are varying sizes notated via A,B,C,D etc? and if the cylinder is worn I'd possibly need a different letter piston then my bike came with? I have a micrometer and dial calipers but what is being measured here?

4) Some people say to have all the parts first but how do you have any idea what you or don't need until you get in there?

Thanks

 

[jmics19067]

Go to a Suzuki dealer and get the factory service manual for your bike and most of your questions would be answered. All should be answered except for maybe honing question, the object you want to accomplish is to not remove any material but lightly scratch the surface of the cylinder in a particular fashion. The manual might state use a 240 grit ball hone and have a 60 degree crosshatch. the 240 grit ball hone is self explanatory but I just try and match the look of the original cross hatch where it isn't glazed. The cross hatch is to help the rings seal better and to hold oil onto the cylinder wall for lubrication

Some people use the ball hone some people just use a scotch brite pad by hand, do not use the spring loaded hard stone hones. Use lots of oil while honing and before you are ready to assemble wash the cylinder out with soap and the hottest water you can stand. Dry either by compressed air or lint free towel/cloth and lightly oil.

 

[EricGorr]

Tips for servicing a RM250 top end

Cleaning the valves: Remove the outer covers and head. Take the cylinder to a local auto parts store/machine shop. Ask for the service of "aqueous power-wash". Its about $10. That is a standard machine with hot, high pressure water mixed with something like caustic soda and de-ruster that is safe to clean the various materials of the valves and bore coating.
Don't take the valves completely apart unless they are carbon-seized after cleaning. If you have to disassemble and clean them don't remove the spring center cartridge from the right side of the cylinder where the link-rod attaches. Just remove the 4mm allen bolt from the valve-yoke and the 8mm hex-head bolt from the right side of the cylinder. Then just disassemble and arrange the parts on a clean sheet in the logical geometric order. The drum valves are marked Left and Right, arrange the parts according to them.
Clean with a soft wire brush or soak in a "Carb Degreaser" can & basket. Use white lith grease as an assembly lube.

Honing: A Flex-Hone with fine ribbons of silicon-carbide is now becoming the factory recommeded standard for deglazing all brands of nickel composite bore coatings. A Flex-Hone from Brush Research in Los Angeles costs about $30
If you can see the hone marks after the cylinder is cleaned, don't mess with honing. If you see deep scour marks on the intake bridges, and gray spots that look like aluminum, then the cylinder needs to be replated. There is an inherant design flaw in the Suzuki RM250 cylinders from 1999 to 2002, with the dimensions of the intake port and bridges. The way to repair the intake port is to heli-arc weld between the top of the intake bridges and the outer intake ports, to increase the top inside corner radius from 2mm to 20mm. Of course the cylinder would need to be bored, faced, plated and honed after welding.

Piston sizes: Suzuki probably offers two different sizes and Pro-X 4-8 sizes in .001 inch increments. Before choosing a piston size, you have to use a dial bore gauge to measure the bore, and chart the sizes from top to bottom, front to back, and side to side. A total of six measurements. Then you choose the piston size that is .002 to .003 inch smaller than the smallest measurement of the bore. Or you can just order the same piston as you had before. A stock cylinder will have an A or B stamped or imprinted on the back corner of the cylinder and piston crown.

Good luck, Eric

 

[GeoffM24]

OK,
Here is the plan, please advise on any fatal flaws etc.

I ordered Erics book last week so I will have that. I will also pick up a service manual.

Tonight I will remove the head and cylinder to inspect condition.

If the cylinder looks good I will clean and possibly scrub with scoth guard.

My head reads "37e2" does that tell me about the stock piston size? If not does anyone know where this is found.

Once located I will order a Wiseco piston of the same size and Moose gasket set for the top end.

I will also order a pin puller and ring installer from Dennis Kirk.

I will also try to clean the power valves with carb cleaner etc or take to auto parts store depending on condition and "spooge".

I will reinstall everything and run a compression test.

Next I will break in the piston slowly.

Will this work? Pros and cons?