Floppy kickstart

If you haven't come across it, you've been lucky. The cause is almost certainly failure of the layshaft bearing. If it gives up completely, the box can lock. If it was mine, I'd dismantle it immediately. The consequences of a complete failure don't bear thinking about.

Sounds like an over reaction but Richard is correct. Don't ride it until that lay bearing is changed. Have a look at the Old Brits site tech for gearbox rebuild info. Usual option is a roller bearing (superblend style) but Mick Hemmings offers a beefed up Portuguese ball bearing with Tufnol cage that also solves the problem and retains the shaft axially.

Occasionally there is another reason for the kickstart flailing and that is the 2nd gear dogs grinding against the kickstart shaft end face. That happened on mine and shims were needed to keep the parts apart. Most likely your issue is a failing Portuguese bearing, cage beaks up.

And when the cage fails the balls fall out and are free to jam between a pair of gears, result is locked rear wheel and pulling the clutch has no effect !!!!!

Order up a rebuild kit and do it all whilst it apart. May need a kickstart shaft as well. Be careful, there a lots of kickstart shafts being sold for AMC boxes at the monent, quality has been demonstrated to be poor in some instances.

Previously richard_payne wrote:

If you haven't come across it, you've been lucky. The cause is almost certainly failure of the layshaft bearing. If it gives up completely, the box can lock. If it was mine, I'd dismantle it immediately. The consequences of a complete failure don't bear thinking about.

Hi richard, im a newby to noc having purchased a mk3 commando about 8 months ago and i seem to have the same problem with my kick starter dropping down on acceleration, do you have to stip the whole gearbox to replace the layshaft bearing or just the outer covers, have worked on other boxes but not sure about commando set up.

cheers alan

The Mk3s had perhaps the least durable layshaft bearings and give up at quite low mileages - often 8000 - 10,000. To be honest, I'd change it as a matter of course.

The layshaft bearing can be changed with the shell (and sleeve gear) in situ but it's a bit of a fiddle and quite difficult to get everything nice and clean. My preference is to remove the gearbox. This means dismantling the primary side which is more time-consuming on the Mk3 but not difficult.

The AMC box is easy to work on with a surprising lack of shims and nothing complicated to align. Get hold of a factory workshop manual and take it slowly. If the selection is out on assembly, it's only one step back to realign the quadrant.

If you're used to horizontally split boxes then it will be a new experience and you'll ideally need to make sure that you have access to an oven for heating the case which will make removal and insertion of the bearings much easier.

Previously richard_payne wrote:

The Mk3s had perhaps the least durable layshaft bearings and give up at quite low mileages - often 8000 - 10,000. To be honest, I'd change it as a matter of course.

The layshaft bearing can be changed with the shell (and sleeve gear) in situ but it's a bit of a fiddle and quite difficult to get everything nice and clean. My preference is to remove the gearbox. This means dismantling the primary side which is more time-consuming on the Mk3 but not difficult.

The AMC box is easy to work on with a surprising lack of shims and nothing complicated to align. Get hold of a factory workshop manual and take it slowly. If the selection is out on assembly, it's only one step back to realign the quadrant.

If you're used to horizontally split boxes then it will be a new experience and you'll ideally need to make sure that you have access to an oven for heating the case which will make removal and insertion of the bearings much easier.

thanks for the info richard, i have work shop manual so will order bearing and give it a go, alan

When it happened to me I left the gearbox in situ and simply and easily replaced the layshaft bearing. Didn't touch anything else. That was about 25 years ago and it's still holding together.

Previously Gordon Johnston wrote:

When it happened to me I left the gearbox in situ and simply and easily replaced the layshaft bearing. Didn't touch anything else. That was about 25 years ago and it's still holding together.

It's quite possible but if debris has got into the sleeve gear or if the sleeve gear bushes turn out to be worn, it's then necessary to strip the primary drive without the ability to lock everything from the back wheel.

The days are gone when my bike had to be fixed in in a few hours in order to get to work the next morning. Given the choice, I'd take my time and dismantle it completely for checking. It's only an easy weekend's work with plenty of tea breaks to do it the long way.

The original Portugese ball bearing was the weak link and was generally replaced with a roller bearing. This sometimes gives problems with excessive side play requiring some shimming. The latest ball bearings supplied by Mick Hemmings seem to be the way ahead and continue to give axial location.

I'm with Richard, do the whole job, then you know exactly what is what. If you search on the access norton website you will probably get the designation of the ball race and you could maybe get it from a bearing supplier. They are not cheap but cheaper than a locked up gearbox.