I bought a 2000 kx125, the person selling it started it with a few kicks when i bought it... Then when I got it home I could only start it buy push starting it... (I live 3000 feet higher in elevation than the place i bought it from) I rode it pretty hard for about an hour, rested and took it out again for another hour and it seemed to work great... I mixed the pre mix @ 32:1 using pump gas... I was having a blast and then I crashed... The bike was running on it's side for a few seconds so I hit the kill switch... I couldn't get it to start again kicking, and even when pushing it... I figured i fouled a plug so I put a brand new plug in and it will not start... I checked the compression and i only got 35 psi... It was real hot out when i was riding... Did I blow the head gasket? (no bubbles in the radiatior when kicking it over with the cap off) Maybe the compression gauge is wrong... I made sure I torked down on compression checker adaptor pretty well until the grommet was squished but not squashed... I did this twice and got a 35psi reading... How could it be running and all i did was crash and then have only 35psi... It's not seized or anything... I don't get it... Was it the pump gas? The heat, and elevation?
lost compression & I'm clueless
- Thread starter dante
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MikeT
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- Jan 17, 2001
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35psi? Man that is low. Something is wrong. I'd pull off the top end and take a look. You might have a seized piston ring. The bike should actually be running rich since you went up in elevation and the day was hot.
Better be safe than sorry. Pull the top end and have a good look at what's inside.
Better be safe than sorry. Pull the top end and have a good look at what's inside.
I would spend $100 for a new piston and rings and go from there. You never know what you are getting with a used bike, especially a 125. Replacing it now would at least give you some peace of mind. Once, I bought a used CR 250 that felt a little tired. When I replaced the top end I found a two inch crack in the piston skirt.
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- #7
MikeT said:
Is their a way to unstick the ring? Or does it just need to be replaced... Someone here at work said to try putting a little oil on top of the piston to possiably un stick the ring... My brother told me never to re-ring an old/used piston but people here seem to do that regularly between new pistons/top ends... Any thoughts on re-ringing used piston? Or is that generally a bad idea...
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- #8
It's just a bummer cause I spent all my cash getting it...and I don't have the cash to spend on parts till i get paid again... I wanted to do a top end on it as soon as I could but I did'nt plan on having to do it so soon! Oh well... Thanks for the help...
MikeT
~SPONSOR~
- Jan 17, 2001
- 4,095
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The ring (if it is seized in there) isn't really "stuck" where oil or a cleaning fluid would help. The ring is actually held in by melted piston material. When you take it out you should see a rub mark on the piston right over the ring holding it in.dante said:
That said, without seeing your bike this is my best guess from nearly 20+ years of experience with 2-strokes. I might be wrong but a through investigation of the your end is definately in order. I can't think of anything else that would make it do that. If it is seized in there, you will need to get a new piston, ring, and gaskets. That usually will cost you anywhere from $65-$100.
Changing the top end (piston and ring) is really not hard. If you lived near Charlotte, NC I'd do the work for you for free. :)
- Thread starter
- #10
MikeT said:
I wish I did live out their I'd take you up on that... I live in the high desert, So Cal Joshua Tree/Yucca Valley area... That's the help I wish I had just someone to be there or to watch do the work or something... I have a street bike, I can do fork seals and even re-shim the valves for adjustments, and I even fixed an electrical problem I once had which was a real bitch... I bet i could do it with the confidence of having someone to coach me the first time... But the way I seem to learn is I screw it up first and then I get it... I just know that's how it goes with me (I learn the hard way everytime)... If I'da tried to do myself I'd be here telling you all how I seized it up and what did I do wrong and all that... I don't even have a manual or anything, and I can't look at the thing not run for a whole weekend after saving for 5 months... So I got an advance from work and took it to the pros, who will have me sorted out for $250.00... Not to bad I guess... And the shop were i go the guys their are cool and expain stuff and go the extra mile for sure...
Thanks again for the offer to help that's really very cool of you...
peace
va_yzrider
Member
- Apr 28, 2003
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dante said:
People here do this on pistons that they know the condition of. You don't know what condition that piston is in b/c it came from someone else. You should replace both and start fresh.
Also, what are the odds that the piston siezed at the exact moment that you crashed? Did you pin the throttle when you crashed?
Further, get a manual for your bike ASAP! Also, if you can work on your street bike as you mention, a top end shouldn't be difficult for you. You will be a bit nervous the first time, but should be able to complete the job successfully.
- Thread starter
- #12
va_yzrider said:
the first time I re-shimmed the valves on my fzr... I miss read the chart and and had to do it twice... Luckley I put shims in that were too small or I would have smashed my valves ends... Same thing with the fork seals I got them put back together and forgot the spacer... The previous owner had a two inch piece of what looked like PVC pipe for plumbing stuck in there... I don't know why but that spacer needs to be in there for the forks to work right... I forgot to put it on, had to dis, and re assemble... I just don't want to even try doing a top end yet... I just wanna ride first thing saturday morning, instead of sweating over, learning the hard way, which is the only way for me... I'm gonna get a manual... I'll have my brother coach me or something next time but he lives 150 miles away...
- Thread starter
- #14
kcsteck said:
I did that still 35 psi... I checked it with the throttle open closed, choke on, off, everyway I could think of... and did it twice... The kick starter offered almost zero resistance... You could push the bike in gear and wouldn't notice if it was even in neutral or not... as if the spark plug was out... when i crashed the throttle wasn't pinned either... I don't know what the odds are of thit happening but that's exactly how it happened as I explained earlier... I think the ring started to stick while hot and when the bike started to cool the ring was then stuck to the piston loosing compression as it cooled... It's probably a good thing I crashed when I did or else I think i would have seized it... however I haven't heard back from my mechanic... I'll post what actually happened when I find out...
also just before crashing, I was on the gas wide opes for I don't even know how long, then I saw some people walking around and slowed down to a crawl, as I passed them... then I got on it again... soon after I crashed... could'nt get it to start again...
