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1997 CR250 Compression???

Joined
Nov 17, 2005
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#1
I was riding along and then my bike died. Like I just hit the kill button. Never able to restart. I cleaned the carb, replaced my cracked reed valves, new iridium plug, replaced gas and it still won't start. I have spark, checked last night. I know I am getting gas to the bowl because if I tip on it's side it comes out the overflow tube. Here's my question: I checked my compression and it is 72 psi w/o holding open throttle and 85 psi with the throttle wide open. What should it be and what things would cause this compression to go away suddenly? I am asking pre-emptively because I am taking off the cylinder and piston to inspect tonight. Thanks in advance for your help!
 
Joined
Sep 12, 2006
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#3
I don't know what Honda's spec is on that particular engine, but yes, it sounds very low and you should have way more compression than that. You have some form of top end damage, I am sure you will know what it is as soon as you pull it apart.
 
Joined
May 31, 2007
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#4
70 psi is definitely LOW for a cr 250. Your compression should should be around 150-190 psi depending on make and model. Another thing that can cause low compression is a washed down cylinder. When checking for spark , what spark color do you have. Is the spark all over the threads is it red spark ect. All these symptoms are very important. Let us know what you find.
Marty
 
Joined
Nov 17, 2005
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#5
Ok, took out piston and cylinder last night. front top piston lip above the top ring cracked off and the top ring is busted. The bad part is the ring or piston has took a chunk out of the top edge of the exhaust port hole, about the size of a pea. So it looks like I may need a new cylinder. Can this be re-sleeved? Or can I smooth out the rough edge of the chunk and put a new piston/ring kit in and go? At least now I know why I didn't have compression.
 
Joined
Apr 26, 2007
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#7
Sounds like the ring broke and got caught in the port which broke the top of the piston out. The cylinder is plated, not sleeved. Send it to US Chrome and they'll weld the damage, bore it, plate it, and hone it for approx. $225. It's best if you send the new piston along and they'll hone it for the correct clearance, but not required. Because the plating is comprimised, it needs to be repaired or it will continue to degrade, exposing the soft aluminum base material which will not hold up.

Marc -
 
Joined
Nov 17, 2005
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#8
Well I went and bought a new cylinder, piston, wrist pin, and gasket set. Should be here this week sometime. Thanks for all the replies and advise. I'm sure now that I have a new top end, the bottom will explode. Murphys law #2. Thanks again!
:cool: