gear box

[Guest]

hello names chris resantly got a cbr 125 2009 with 7,000 miles on clock been on road for over 2 years naw and with this new bike i found that it lunges some times in gear when going down the road for no reson normaly in 4th doing about 6000 revs. but saterday going to work it lunged then masive gronching sound like gears where grinding and it redlined iv seen blokes at work how race bikes and they have no idear as it only does it every naw and then and its not under lode as we have tested it by doing burnouts in car park so its not under lode that is the problem. any hellp would be good many thanks chris also is it normal got the gear box to be stiff eg not going down throw the gears from 6 to 1st with cluch in and not leting it out as u go throw e.g cluch in and go straght fron 6 to 1st it gets to 4 and goes no further have to let cluch out to keep going down

[eastanglianbiker]

welcome to the forum if you plan on sticking around pop into newbies and introduce yourself this is a good forum with lots of folk willing to help if they can.right are you sure chain tension is corect as you could be suffering whiplash of the chain back through the gearbox if thats ok then chances are the gearbox selectors will need looking at and checking and to do that its an engine strip job

[Adam]

I don't have a clue when it comes to gearbox's but I find on my bike if the chain isn't tensioned properly the gears aren't smooth so might be worth a check before you try anything else?

[Guest]

Chain whipping can play a very big part in it, it can also make the bike "strutter" through its rev's..

Almost reminds you of misfiring a little..

So the chain would be my first bet..

Also make sure the chain hasnt jumped off the front sprocket.. That would make your bike redline instantly. from having drive and weight on the engine, then suddenly nothing...

After 7k miles, i cant see it being a gearbox issue as such, But the gear selector could also be worn..

It could be something simple, like the gear selector return spring lost its tension over the years and wont hold the gear properly.

Or it could be something more serious..

Id defo check the chain tension first..

I normally go for around an inch of chain free play, up and down, something around the ball park, and you should be fine....

Dont go too tight though, or it will damage your sprockets and put excessive strain on your chain..

[Guest]

hi the chane is tight but i will have to have a look at the sprockest on the front but its only just had its mager survice at 6.800 miles so would of thought they would of looked at that fir me

but will have to have a look for pice of mind

[Grumpy Old Git]

It could be something simple, like the gear selector return spring lost its tension over the years and wont hold the gear properly.

..

 

Or, the spring mis-seated / snapped.

I'd look at that once Im certain the sprocket is OK.