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Picked up a 95 RM 250 with low compression

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Hey all, I am brand new to dirt bikes. I picked up a 95 RM 250 that occasionally will start and run but only after I am out of breath and sore from kicking. First thing I did was download the manual. Today I bought a compression gauge and bike measured at 93 psi cold, throttle open, multiple kicks. Put a little 2 stroke oil down the plug hatch and compression jumped to 130 psi. I assume I need a new top-end. I have a cylinder bore gauge on order and my plan, after scouring forums for the past week, is to measure the inside of the cylinder to see if it is in spec or if its been bored out, and measure to the piston with some calipers to double check it was running a std piston. Then I was going to order a kit to fit whatever my results are and see if this does the trick. I can easily hand crank the kick starter as well and after I poured a little oil down the plug hole I was able to much better find TDC and could feel the improved compression. However, still didn't start. Am I going down the right road? 

 

I was also planning on cleaning the carburetor out. I have no idea what size jets are in it, and haven't researched how to determine which are which. I also have not adjusted the choke as I figured with that compression its time for a rebuild and then get into the fuel delivery? Thoughts?

 

Sorry so long, been making mental plans but I do not know anyone who knows anything about these bad boys. Also, no idea if t  his has any mods or not. Thanks!

IMG_1797.JPG

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No replies. Sad. 

 

Well I used the manual and completed a top end rebuild and this is the most mechanical thing I have ever attempted. The cylinder was shiny but the old piston was cracked vertically. I checked bore and was in spec, check ring gap, in spec. Install went well.

 

I spent about 45 min breaking the engine in, started first kick, compression was at 170. 

 

Then today I was riding around my yard in first gear, barely throttling it and all the sudden the engine starts to rev out of control for about 3-5 seconds like I was at full throttle, way way faster than I have revved it thus far and then it dies like it ran out of gas. I am holding the clutch in during this so keep the bike from killing me. After it quits, I notice the kick starter is locked up. I inspect the bike and I notice that the coolant drain screw on the water pump is like 1/4 inch out and dripping coolant, I am like 99% sure I tightened this piece up with my hand but never went back to torque it after the rebuild so it worked its way loose.

 

I drain the coolant and its good amount in there. I drain the oil and there is a lot of small metal particles in it but no big pieces and it is grey colored. I never opened the water pump housing so not sure whats going on in there. I took the top end off and looks great. No visible wear. Crank is locked up though I can see no damage from up top.

 

A few questions...

 

1) If I overfill coolant would that cause it to get into the engine and cause this problem?

 

2) Would air getting in through the water pump let out screw cause this problem?

 

3) Should I just get the tools and a rebuild kit and plan to rebuild the bottom end?

 

4) What else should I check before I dive in?

Edited by jeffls1234

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No replies. Sad.

Well I used the manual and completed a top end rebuild and this is the most mechanical thing I have ever attempted. The cylinder was shiny but the old piston was cracked vertically. I checked bore and was in spec, check ring gap, in spec. Install went well.

I spent about 45 min breaking the engine in, started first kick, compression was at 170.

Then today I was riding around my yard in first gear, barely throttling it and all the sudden the engine starts to rev out of control for about 3-5 seconds like I was at full throttle, way way faster than I have revved it thus far and then it dies like it ran out of gas. I am holding the clutch in during this so keep the bike from killing me. After it quits, I notice the kick starter is locked up. I inspect the bike and I notice that the coolant drain screw on the water pump is like 1/4 inch out and dripping coolant, I am like 99% sure I tightened this piece up with my hand but never went back to torque it after the rebuild so it worked its way loose.

I drain the coolant and its good amount in there. I drain the oil and there is a lot of small metal particles in it but no big pieces and it is grey colored. I never opened the water pump housing so not sure whats going on in there. I took the top end off and looks great. No visible wear. Crank is locked up though I can see no damage from up top.

A few questions...

1) If I overfill coolant would that cause it to get into the engine and cause this problem?

2) Would air getting in through the water pump let out screw cause this problem?

3) Should I just get the tools and a rebuild kit and plan to rebuild the bottom end?

4) What else should I check before I dive in?

If you overflow the coolant it will just go out the over flow.

I've never heard of air getting through the water pump but it's possible. If there is metal in the oil then it doesn't seem like the crank would be the issue. I would take off the clutch cover and see how everything looks in there.

Don't buy any parts till you get it all apart and find out what you need. Then you can order it all at once.

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Thanks for the advice. When I drained the oil for the topped rebuild there were small slivers of metal in the oil as well. I thought the shifting seemed a little stiff. I will check out the clutch first and check back in here for next steps. 

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sounds like it ran out of gas or some  sort of vacuum leak or your throttle cable is messed up 

 

i know that bikes rev out of control before they run out of gas from an idle to high rev to death the motor leans out 

Edited by 78SuzyQ

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Interesting. The gas tank was almost empty just aclittlenbit left in it. So reving out of control and engine seizure can happen from running out of gas? Crazy.

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A 2-stroke's lubrication is dependent of the fuel/oil mix,

running out of fuel = no lubrication

plus leaning out the air/fuel mixture = lean surge / high idle

 

170psi is still low for a freshly rebuilt 250, should be closer to 200psi

 

As that is an older engine with an unknown past maintenance record, as a preventative measure

you really need to do a leakdown test on as the crank seals are likely worn out.

Edited by mlatour

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