Posts
94
Joined
11/6/2015
Location
Alabaster, AL
US
Edited Date/Time
2/27/2021 6:58pm
Hi All,
I have a 2002 CR250 that I purchased new in 01 and have done many things to the bike over the years. A while back, I sent the cylinder jug off and had it bored to a 265cc. I don't have much time to ride the bike but over the past couple of months, I noticed a knock/pop starting to develop gradually in the engine. It is not a constant knock but it sounds more like one knock/pop when I blip the throttle. I can hear it and slightly feel it when it happens and is something that has slowly gotten worse. I thought maybe I had a bottom end issue causing the piston to slap. I have the top end of the bike torn down so I checked the rod for any up/down slack. There is absolutely no up/down play in the rod. Like I mentioned, I don't have much time to ride the bike but have replaced the rings a few times since the engine was bored. I have included some pics. Please see below:
This is a pic of the head. There was alot of wet carbon build up and was able to be wiped off cleanly.
This is a pic of the top of the cylinder jug and piston. The piston has some burned on build up. Is this piston still ok to put back in the bike? I've rebuilt the bike a few times over the years but don't remember this much build up on top of the piston.
This is the font/rc valve side of the piston. There are some scratches on in but nothing deep.
One more pic of the top of the piston out of the bike.
Also, when I pulled the jug, I noticed that the flaps for the exhaust valve were very loose. So much so that they would make a clanking sound when I hit the jug. I don't recall this being the case on any bike I've rebuilt. I could be way off base but I feel like this could be the source of the pop when I blip the throttle. I uploaded a youtube video of what I'm talking about. Please see below.
https://www.youtube.com/watch?v=CrzA92DTogI&feature=youtu.be
I'm looking for any professional thoughts, opinions and advice that you guys may have on replacing the piston or what the knock/pop sound may be.
Thanks in advance,
David L.
I have a 2002 CR250 that I purchased new in 01 and have done many things to the bike over the years. A while back, I sent the cylinder jug off and had it bored to a 265cc. I don't have much time to ride the bike but over the past couple of months, I noticed a knock/pop starting to develop gradually in the engine. It is not a constant knock but it sounds more like one knock/pop when I blip the throttle. I can hear it and slightly feel it when it happens and is something that has slowly gotten worse. I thought maybe I had a bottom end issue causing the piston to slap. I have the top end of the bike torn down so I checked the rod for any up/down slack. There is absolutely no up/down play in the rod. Like I mentioned, I don't have much time to ride the bike but have replaced the rings a few times since the engine was bored. I have included some pics. Please see below:
This is a pic of the head. There was alot of wet carbon build up and was able to be wiped off cleanly.
This is a pic of the top of the cylinder jug and piston. The piston has some burned on build up. Is this piston still ok to put back in the bike? I've rebuilt the bike a few times over the years but don't remember this much build up on top of the piston.
This is the font/rc valve side of the piston. There are some scratches on in but nothing deep.
One more pic of the top of the piston out of the bike.
Also, when I pulled the jug, I noticed that the flaps for the exhaust valve were very loose. So much so that they would make a clanking sound when I hit the jug. I don't recall this being the case on any bike I've rebuilt. I could be way off base but I feel like this could be the source of the pop when I blip the throttle. I uploaded a youtube video of what I'm talking about. Please see below.
https://www.youtube.com/watch?v=CrzA92DTogI&feature=youtu.be
I'm looking for any professional thoughts, opinions and advice that you guys may have on replacing the piston or what the knock/pop sound may be.
Thanks in advance,
David L.
what premix and ratio are you running? That exhaust bridge is not getting enough lubrication judging by the scoring on the piston exhaust side
Eric gorr is the man to talk to if you need to have it repaired. I had to have mine repaired whenever I was tearing down my CR a few years ago.
I'm running a 32:1 ratio for my gas/oil ratio using Maxima Castor 927.
Is it normal for the exhaust valves to be as loose as they are in the video I posted? And rattle around like that?
The Shop
even without measuring just looking at it, that piston is done.
Is it common for the power valves to be loose and rattle around?
Upon teardown i noticed front of piston, power valve side, was eaten away and fried the rings.Typical too lean, dirt/sand intrusion, etc. I also noticed the exhaust bridge was scraped bad seemingly just superficial, as well as the pistons mating surface. Figured it was due to the rings failing. Also noticed a hairline crack in coating, running horizontally across the top of the bridge.
Found out from buddy, turns out the cylinder was previously cracked, re welded and coated by U.S. Chrome. i picked the coating off with a flathead, and exposed the crack. The coating failed and exposed a solid crack completely through the top of the exhaust bridge, where it "T's" to join the rest of the upper cylinder walls. My buddy says its the same crack as before, no more, no less.
Long story short, i spent my days obviously looking for a big bore it, only to end up at the Eric Gorr 265 kit, which i passed on. Bought a brand new stock factory Honda cylinder with power valves installed. The first thing i noticed was the difference in slop/play in power valve action. Mainly the shaft on the used cylinder would slide in and out, id guess about an 1/8", and the sloppiness of the valves opening and closing. The valves would close just by gravity alone. Where as the new power valves had virtually zero shaft wobble and the power valves had a light drag, and the valves would barely stick in the fully open or closed position. smooth action though, with a "tight" feeling when fully open or fully closed. For example, the old power valves were easily actuated by my thumb on the shaft. Sloppy and loose, and I could hear almost the light rattle when the valves would fully open to lockout, and bottom out to close. Had that really light "ting" sound . The new valves, tight as can be but smooth.Had the same "ting" sound when fully open/closed, but sounded more solid, like the "ting" doesn't ring out like old cylinder did. Almost like it seats better.
Just some things i noticed during rebuild i figured id mention.
Performance feels incredibly more responsive off bottom end. But i also bought the 05+ base gasket so i knew the off idle gains weren't in the power valves alone. Just my .02c...
P.S. is there any use for my old cylinder? Core trade in? Repair, etc. Any other than U.S. Chrome?
Super thread revival here, but did you ever figure out what the source of that knock was? My '02 CR250 just started making what sounds like that identical knock...right after a blip (warmed up), 1 or 2 "taps" that you definitely hear and feel in the grip, and even a slight interruption in the RPM while the engine returns to idle. Can't tell if it's a detonation ping or if maybe something is mechanically failing in there...but it does not sound good and I shut 'er down. Checked my flywheel weight to be sure, tried again, and same thing.
Do you remember what that issue ended up being?
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