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CB250 gearbox/chain (shifting problems)

Discussion in 'Technical and Troubleshooting Torque' started by pt, Apr 18, 2005.

  1. I've got a 98 cb250 and the gear changes are pretty shocking. when i bought it it wasnt easy to put the bike in neutral. took it to the mechanic suspecting the problem to be somewhere in the clutch and he replaced the clutch. it only made a slight difference but a difference all the same. now recently, after the bike gets warm, its near impossible to shift the bugger into second. most of the other shifts are ok, albeit a bit clunky. the oils been changed and there doesnt seem to be a leak. i beleive the chain may need changing or adjusting but i have no idea how to do either of these. another thing thats crossed my mind is that the gearbox itself is buggered? its got about 30000 Ks on the clock and had two learners on it before me. maybe the gearbox is just screwed? does anyone have any ideas as to what the problem is and if it is the gearbox, how much is it going to cost me?

  2. Check the chain first. Don't start bike. Sit on the bike. Both feet flat on floor just level with footpegs. Reach down by inside left leg and locate chain. Push chain up with index and middle fingers. Chain should move up a maximum of 20mm. If more or less than that will require a chain adjustment. Also look at rear sproket and determine if there is uneven wear on it. That is, are any of the teeth excessively worn, worn at odd angles or shapes etc. Can also indicate loose chain or wheel misalignment. If got to do adjustment, put bike on centre stand. Check marks on back wheel. On swing arm left and right hand sides near rear wheel hub, there are two cutout windows. Located inside these windows are a series of marks. These marks indicate whether the chain is at its maximum extension or whether further adjustment can be made. If further adjustment can be made, loosen rear wheel hub bolt and adjust small bolts on rear of left and right sides of swingarm. Make sure the same marks are lined up on either side. Tighten rear wheel hub bolt. Lubricate chain. Get one of those spray on wax type lubes, use it every week if you're using the bike 9-5. If no adjustment can be made, then new chain will be required.
  3. thanks. thats aweome. ill do that tomorrow. the two nuts on the ends of the swingarm need to be adjusted exactly the same amount or can one be adjusted and the other not? im assuming both have to go out together... thanks again. if that doesnt help the gear changes i guess ill have to start looking inside and most probably at a new gearbox then...
  4. Both marks should be the same in each window on either side of the swingarm. If 1st mark is in window on left side of swingarm, looking towards front of bike then 1st mark should be aligned in right window on right side of swingarm. Yes both those little screw/bolts on end of each side of swingarm should move in and out together. It's the marks that are important. When I got my bike back from the shop I found that 1st mark was aligned on one side of bike and 2nd mark on the other side of the bike. Needless to say it made cornering a little bit snakey.
  5. Be wary following that method tho, to align the rear wheel. If I use the same marks on either side to adjust my chain tension I ended up with a badly misaligned wheel.

    Once you've got the wheel alignment ok, I believe a safer method is to go with the same movement on each side (one rotation here, one rotation there... etc, etc). Or, you can line up the wheel each time with the straight-edge method.
  6. ok so i finally adjusted the chain and it made no difference. does anyone know a ballpark figure for a new gearbox? i've already replaced the clutch and tightened the chain and the rear sprocket is clean and in ok condition. is there a possibility that the front sprocket is gone? oh yeah. how much is a new chain about as well?
  7. New chains vary greatly in price, anywhere between $100-$300 depending on type and quality. For this bike (I own one as well) you can get a really good one for the $180-$200 mark. Don't know about new gearbox or overhauling the old one though.
  8. PT, I think you'll find its more a feature of the CB250 than a fault. I had one for 14 months, gear changes were often interesting, and trying to get the thing in neutral was a pain in the @ss. Try experimenting with different oils, I noticed a bit of a difference with different brands, but it was never fantastic.

  9. Make sure your clutch lever is adjusted properly. Too much free play at the lever could cause clunky/difficult shifts. (I am assuming it is a cable clutch)
    Your gearbox may be on the way out, but check the simple/cheap things first before you go handing over money to someone.
  10. is there a possibility that the clutch plates could be like, re-engaging cause theyre moving TOO far? i dunno. when i got the clutch plates out i think some moved and some didnt... dunno. anything for a cheap fix. and i don't think it's a feature. it is impossible to put the bike in neutral while running and stationary and when the bikes warm, shifting up and down through 1st to 3rd is extremely difficult.
  11. It sounds like the clutch might need adjusting... if the cluch is not disingaging propely the gear changes may be difficult... in most cases you can not adjust the cluch coz the clutch cable is strached so you might want to replace it... if that fails... than the selector could be buggered but usualy that results in the gears sliping out of the gear...
  12. i dunno dude. i would have to ride it to tell you. some models
    by design are very clucky and hard to change. it could
    be a damaged selector, poor tolerance gear/assembly... or
    it could be you. it could be a dragging clutch. dunno.

    most bikes have owned have to be loaded for smooth and
    damage free gear change (ie, accelerate, then gear change).

    i would go up and down the gears when the motor is off/bike
    stationary and see how easierly they fall in (while rocking
    the bike back and forth as you are doing it)-- see if any weird
    sounds or clunking takes place.

    do this 20 times. if you do this 20 times and you can freely
    go up and down the gears, then i would say that gears
    can be elliminated.

    if it is the gear box... then, i wouldn't worry about it. splitting
    cases is expensive and risky. i would just make 2nd gear
    your 1st.

  13. I've had similar problems with Bond but by finding a good mechanic as in Mike at OCD Racing who changed my front & rear sprockets & chain it improved him dramatically on the up change. Going down I found I had to go thru each gear not just clutch & jump down to 1st then I had no probs finding 1st or neutral. If you're having trouble with neutral try letting the clutch out until it just catches then pull it in again & try again!