Bsa 650 star , for a few months now my bike has always had a slight clunk when going into 1st, just been out on it and it is getting louder and up to 3rd gear, coming down the box is smooth, but accelerating and changing up the box sound like hitting the chain guard with screwdriver sound. any ideas as to what could be happening.
This is a bit of an odd one because down shifting tends to show up more problems than up shifting which is normally a little gentler on the operation of the gearbox. Clutch drag can cause gearbox noise but if you can find neutral reasonably easy then this can be ruled out.
The only thing I can think of external to the gearbox that can potentially cause noise from gearbox changes is a loose gearbox sprocket which is worth checking if you can. If ok, I would be tempted to cycle through the gearbox with the bike on the centre stand with and without the engine running to see if you hear unusual sounds and, if so, might help to confirm it is actually coming from the gearbox rather than the rear chain, for example, slapping against the chain guard.
Unfortunately, if the noise is coming from the gearbox, you may be forced to take it apart to check for internal problems.
Come to think of it yesterday i was struggling a bit to get it in neutral, Maybe its time to replace the clutch. ill do a few checks to see what i come up with. i have noticed it slipping a tad when i give it full throttle then settles down again.
Update on the problem.
The 4 rear nuts where loose on the sprocket, they undid by hand, cleaned them with contact cleaner in the threads, an the threads on the studs, and put some thread lock and tightened them back up, all sweet now. ive only just had chance to look at the bike, lucky there was nodamage to the sprocket or the studs.
I just thought i would come back on this as its a first for me.
Thanks for letting us know and glad it wasn't a gearbox problem :)
Me too spaceman. i had alsorts of thoughts clutch basket worn with slots etc. Thats why i always come back i may just help some one else out.