is a clutch problem really a gearbox problem?

[Chris T]

Hi guys - it is a number of years since I have posted.

I have a 1970 roadster. I was recently out riding on one of the few rides per year that I do, and experienced a very badly slipping clutch (I thought) and eventually could also not change into third or fourth gear from second - I can get first, second and neutral. Ulitmately stopped and had to be trailered home as when I stopped the motor was just spinning with the bike in gear and no power going through the transmission at all; I could not restart the bike as the kickstart just slipped. I thought that my clutch needed replacing, and have just installed new barnett plates. However, I still can't get the kickstart to engage when the bike is in neutral; seemingly no matter how I adjust the clutch. I also cannot move the gearbox past second gear.

I am now thinking that the issue might be gearbox related rather than clutch. Looking at my Haynes manual and posts in this forum - "gearbox rachet pawl spring" and " I thought it was clutch slip but I think it might actually be a gearbox issue" I am thinking that iat least part of the issuemay be a worn ratched assembly or adjustment of the pawl spring. I have not yet drained oil from the gearbox to see if there is any metal contamination that would indicate failed parts.

The Haynes manual says that a reason for the kickstart slipping might be a worn ratchet assembly and/or pawl. Would that also affect the ability to select third and fourth gear? If not, what would? Haynes says gear selectors not indexed correctly or selector forks bent or badly worn.

I have had the layshaft replaced during my ownership - over a decade ago - but only a few thousand k's ago, when the motor and gearbox was rebuilt by the late Bob Nesbitt; ex RGM and then owner of an NZ Norton racing team.

I would be grateful for your thoughts.

I am no mechanic; and have never been inside this or any other gearbox. That said, I did years ago completely strip and rebuild the bike - other than motor and gearbox - and have a comprehensive tool kit and bike lift. I am completely ignorant of gearboxes. The bike is not located near to any britbike mechanic (so far as I can tell) so my choices are to remove the gearbox and take it to someone to investigate, or have a go at disassembing it myself; which I am a bit apprehensive about; but if it includes fine work and specialist knowledge.

So I would be very grateful for:

* any thoughts on the possible causes of these issues;
* whether I should leave the diagnosis and repair to an expert - which will probably require me to remove the gearbox and take it somewhere - which I am kind of reluctant to do until I have at least tried do diagnose the issue;
*what I can do myself to attempt to diagnose the issue; and whether I should attempt to fix it or leave it to an expert.

Thank you.

 

[MichaelB]

Start with the primary.
Pull the cover.
1. Very primary chain is in place.
2. See if you get clutch action with operating the clutch.
3. Put bike on center stand and/or elevate the rear wheel, rock rear wheel and see if you can change gears.
4. Disassemble clutch, observe clutch spin when pushing kicker, should be smooth.

I would verify all these before gear box tear down.

 

[ashman]

Its not that hard to do in 1979 when my lay shaft bearing blew i never rebuilt a gear box or any motors for what matter, a good workshop manual, comon sence and taking your time, if you can pull you GB out you can rebuild your box so simple and you get to know your bike better.
When you pull it down just lay your parts out in order, and put it back together in reverse, as you go look for any signs of wear, lose bits, broken or worn bushes etc etc.
My first time was a bit scary but turned out it wasn't and so far i have rebuilt a few since the late 70s, the GB is pretty simple in design and ease to work on so don't be put off doing it and use the right WW spanners/socketfor the inner case nuts.

Ash

 

[Torontonian]

Loose mainshaft nut ?

 

[gpzkat]

The last area worked on (clutch) is the first to start checking, IMO.

 

[Tornado]

Lots of on-line video's on how to strip and rebuild the gearbox, in the frame, if it comes to that. I studied them and did my whole GB, first timer, all springs/bushing/bearings/seals, in the frame.

But check oput what's happening in the primary case first. It may just be a clutch assembly issue (adjuster on the pressure spring) or perhaps a problem with the clutch cable, where is attached inside the inspection opening of the GB...

 

[kommando]

A loose alternator rotor can also cause clutch slip. Based on the idiocy of my mechanic where he worked last is always my first check item .

 

[phippsy]

The circlip behind the clutch if it has been done up to tight causes no end of problems

 

[Tornado]

A loose alternator rotor can also cause clutch slip. Based on the idiocy of my mechanic where he worked last is always my first check item .

I think i had that same guy do my engine work...no shake-proof washer under the rotor nut...backed out and did a nice job on the timing scale and alternator insulation.

 

[Torontonian]

The circlip behind the clutch if it has been done up to tight causes no end of problems

Thin down the MK111 electric starter hardened circlip and tap it into the mainshaft slot , home .
Eliminate the soft bend-over tab washer . Substitute a hard washer and use blue Locktite on clean threads .

 

[acotrel]

Norton Commandos were made by cricket players. How difficult can it be to pull one apart and check it ? It is not an MV Agusta which anyone can stuff. My mate had an agency - no bill for repairs was ever under $5000. I cannot remember what is inside any of my gearboxes - when I pull them apart, all of the bits know where they belong. The only thing with a Norton box - when reassembling it, there is a way of timing the gear change. I forget it, but it has never been a problem. Just check that you are able to select all of the gears, before starting the motor.