Sudden Loss Of Drive. CB350F

[gtmdriver]

I was accelerating the bike hard up a slight hill and when I let the clutch out in fifth fear the revs shot sky high and there was no drive.

At first I thought that I had missed the gear but I checked and it was engaged correctly.

I slowed down and tried all the gears and the symptoms are the same in every gear.

There is drive at low throttle openings but as soon as any sort of power is applied drive is lost completely.

It doesn't feel like clutch slip. A slipping clutch is usually less noticeable in the lower gears but gets worse in the higher gears. This problem is much the same in every gear. I'm wondering if I might have stripped something in the primary drive.

Are there any known issues which I should check first?

[K2-K6]

Can't immediately think of anything but the clutch.

Primary must be delivering drive to gearbox to have any semblance of drive at all.

They are only small diameter of clutch, if it's gone up in smoke it won't have much in the way of torque transmission at all and whatever the ratio. There's not much travel to lift the plates to open either, so it won't take much to be open in pure wear.

You could try backing the adjustment mechanism out to see if it's holding the plates open.

[robvangulik]

No sprockets without teeth? The chain hasn't come off the rear sprocket? Does the clutch lever feel different?

[gtmdriver]

Both sprockets are fine and the chain is correctly on the sprockets.

The feel of the clutch lever is the same BUT there is more free play in the cable at the lever than there was previous to the problem.

[K2-K6]

You'd need to check the clutch adjustment at engine end as that's relative to how much material is on the plates.

Not the cable 

[gtmdriver]

It's not so much the adjustment as the fact that it's suddenly changed.

[K2-K6]

That's why there's a need to check it.

The engine mechanism leveraging the clutch plates to open is set relative to the total accumulation of the plate's thickness within the clutch pack, the cable is then adjusted to fully operate this (essentially separate) device. Once the plates show significant deviation from original set point the error is "seen" within the cable, but with the problem existing entirely within the clutch operating mechanism after the end of the cable.

[Nurse Julie]

Has the ball bearing fallen off the end 🤔

[McCabe-Thiele (Ted)]

Certainly clutch slip would imho  be my first thought - if you have all the gears & it pulls at low revs it's got to be connected with it slipping either due to wear, the clutch operating system or synthetic oil being too slippy by half. Or even a bit of all three.

I guess you need to start with the obvious first check - cable - end operating mechanism - then check the plates themselves.

[gtmdriver]

So I pulled off the sprocket cover and checked out the front and rear sprockets and splines then moved across to the RHS.
I drained the oil ready to remove the clutch cover then took off the kick-start and footrest.
As I came to release the clutch cable from its abutment on the cover I found the problem. An M6 Philips screw about 30mm long (origin unknown so far) had fallen and jammed between the clutch operating lever and the casing and was stopping the lever from fully returning so the clutch was stuck partially disengaged.
Since the clutch had been slipping for a while as I crawled home I decided to continue with the stripdown so that I could check the steel plates and renew the friction plates and springs.

It turns out that there isn't a ball bearing in the operating system. There's a short ball ended pushrod between the internal operating lever and the spring plate.

[McCabe-Thiele (Ted)]

So I pulled off the sprocket cover and checked out the front and rear sprockets and splines then moved across to the RHS.
I drained the oil ready to remove the clutch cover then took off the kick-start and footrest.
As I came to release the clutch cable from its abutment on the cover I found the problem. An M6 Philips screw about 30mm long (origin unknown so far) had fallen and jammed between the clutch operating lever and the casing and was stopping the lever from fully returning so the clutch was stuck partially disengaged.
Since the clutch had been slipping for a while as I crawled home I decided to continue with the stripdown so that I could check the steel plates and renew the friction plates and springs.

It turns out that there isn't a ball bearing in the operating system. There's a short ball ended pushrod between the internal operating lever and the spring plate.

Glad you sorted it - why replace the springs they should still be okay - even the clutch plates might not have been badly affected. I would be inclined to leave the plates & springs as they are and try it now you have found the culprit !

[gtmdriver]

The clutch was slipping for quite a while so the friction material may well have overheated. The plates, springs and a new gasket come as a kit from DSS for only £39 so I'm doing the lot while I'm in there. I'm also fitting a new kick-start oil seal as that was weeping slightly.

[TrickyMicky]

I think I would take a while checking to see where that M6 screw originated from!

[philward]

And also be grateful the errant M6 screw didn't jam in a gear, etc!

[McCabe-Thiele (Ted)]

The clutch was slipping for quite a while so the friction material may well have overheated. The plates, springs and a new gasket come as a kit from DSS for only £39 so I'm doing the lot while I'm in there. I'm also fitting a new kick-start oil seal as that was weeping slightly.

Being a wet clutch it is unlikely to have burnt like a dry car one does but then peace of mind is worth £39 I guess.
Any joy in identifying the likely origins of the screw you found ?