CR125 Odd problem

plumma · Apr 9, 2006

hey, my 02 CR125 has barely any compression when I kick the kicker, and when it does start it has absolutely no powerband. Also when I'm riding there is a distinct flapping/rattling noise coming from the engine area. Any clues? I sure hope its not a top end, cause i just replaced the top end not too far back.. any feedback would be great!

oh yeah, i pulled the plug and it was bone dry. is it reeds? im totally stumped..

archerthr · Apr 10, 2006

Hi, the same thing happened on my xr250r , except it didn't make a rattling noise. When ever I kicked it over, it had none or very little compression. Turns out it was my decompression valve, it wasn't adjusted correctly. If this thing is just a little off, it makes a BIG difference, believe me, I must of kicked that thing over 300 times before I figured out what it was. Thanks,
-Kyle :bang:

zx6rman96 · Apr 10, 2006

i had that problem once...there's a woodruff key located by the flywheel...mine shattered once...replaced it..and waala....good as new....also might want to check your stator for corosion..etc...

Gibby · Apr 10, 2006

archerthr said:
Hi, the same thing happened on my xr250r , except it didn't make a rattling noise. When ever I kicked it over, it had none or very little compression. Turns out it was my decompression valve, it wasn't adjusted correctly. If this thing is just a little off, it makes a BIG difference, believe me, I must of kicked that thing over 300 times before I figured out what it was. Thanks,
-Kyle :bang:

Um as far as I last knew 2 strokes dont have decompression!!

quetip · Apr 11, 2006

head gasket maybe?

plumma · Apr 11, 2006

Thanks for the tips guys, i'll definitely look into these ideas.

plumma · Apr 11, 2006

ok I just pulled the top end, the cylinder is going into a shop to be specd, and the piston looks scored, with some light burn marks up and down the sides.. theres also some tiny grooves in the piston on one side. I will probably be replacing the piston, and see what a shop says about the cylinder. I might have to get it sleeved or something. You guys think i'm on the right track? thanks for helping

zx6rman96 · Apr 11, 2006

yeah right track man...hopefully it's not that bad where it has to be resleeved. Hopefully a good honing will do it.. I would def put a new piston in. go with a vertex..same price as a wiseco..much better piston tho..I made the switch and won't use a wiseco anymore. Around 95.00 for piston,rings,circlips,and pin. There's like a special coating on the skirt of the piston for extra life. Just my opinion tho...have fun

littlenasty · Apr 11, 2006

yes, my yz wasnt getting good compression, i put new piston and rings in, and WALAA!!

dante · Apr 11, 2006

did you install the ring unside down?

MOTOX888 · Apr 11, 2006

uhhhhhh... That rattleing sound means that there is excessive cylinder to piston wall clearance, and you are very lucky you took it apart when you did, or else you would have probobly broke the piston skirt off, causing you big $$$$
I am guessing that the cylinder plating is very worn............
And if it is dont get it sleeved, get it replated as it will last 100x longer, and the plating attracts the oil (Nickasil)
A cyl. sleeve is roughly 80 bucks plus labor to have it installed, and to get it replated, that is around 200.....but if you keep your airfilter clean and well oiled, the next time you go to do a topend all you will have to do is just replace the piston and rings, and not the sleeve again. So all-in-all to get it resleeved two times is going to cost more than having it replated 1 final time (if you keep your airfilter in good condition)
-Chris

plumma · Apr 12, 2006

Thanks for the replies, I'll see what my friend at the shop says, hopefully It's just a rehone job. And piston replace.

steve101 · May 10, 2006

did you fix the rattle because i think mine does the same

plumma · May 10, 2006

yeah i fixed the rattle. It needed a new top end. I replaced the cylinder and piston, and now it runs like new, no rattle or anything. Kinda a big bill, but it fixed it.

steve101 · May 11, 2006

did you have to replate the cylinder also what cylinder is yours a or b thanks

plumma · May 11, 2006

No I didn't replate, I ordered a new B cylinder from motorsport outlet (awesome btw) and now it runs like crazy, I'm so happy. I learned that if the engine area starts rattling like it was, it's probably due for a top-end.

Kevin003 · May 11, 2006

How much did that new cylinder put ya back? Im just wondering becuase its always nice to have a backup.

plumma · May 12, 2006

the new B cylinder was $250.

steve101 · May 12, 2006

how come you had to get a new cylinder can you replate the old one

plumma · May 13, 2006

I was going to have the old cylinder bored out, but the machine shop messed up the cylinder and come to find out you cant bore an aluminum cylinder without first sleeving it.. so to avoid all the hassle I just ordered a new cylinder with a top-end kit.

offroadeast · May 15, 2006

When you buy a piston you have to make sure that it is the right size. If it is too small then the rings won't seal and all off the pressure will get by them. The shop that you took it to can help with the measurement and ordering the proper sized piston.

Before you put your bike back together, check and see if you can move the rod up and down. It sounds like your bottom rod bearing is gone. This will cause the noise that you mentioned. When the engine goes around TDC and BDC, the loose bearing will let the skirt of the piston contact the cylinder wall. If the bearing is bad, you will just keep ruining pistons and waisting your money.

I hope this might help!

OFE

plumma · May 15, 2006

Well I rebuilt the engine, replaced the cylinder and piston, clutch, repacked the silencer, new chain, and now the bike is a bat outta hell. Also it sounds great, and yeah, when I had it apart I checked the crank and it has no play in it, I replaced that early last year cause I cold-seized it..

CR125 Odd problem

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