Dommie Kickstart Issues

With the kick-start fully returned and the GB in neutral, does the rear wheel turn freely?

The layshaft runs in a bush inside the kickstart shaft if I remember correctly. Did you change that bush? If that bush was tight on shaft and bushes supporting the kickstart shaft were a bit loose, maybe kickstart shaft is twisting and grabbing the layshaft and turning it. 

I fitted a new Layshaft roller bearing, carefully measured the end float with a Dial gauge and fitted Isso shims allowing 10 thou float.   That just locked it all up !!.  I then took  Hemmings advice and forgot the shims ,  let it all hang out ! .  Worked fine.

Sounds like a  bush  is too tight, there are pattern parts around that are not good. Also the  4th gear can be fitted the wrong way round.

With all assembled can you feel a trace of end float on the KS  in all its arc ?. Too much radial play in the KS bush gave me some similar issues. The old issue with  a bad clutch spider axially loading up the box and clamping the mainshaft to the sleeve gear gives some odd issues and is very hard to spot.

Several areas that I would be checking.......some mentioned above already.

1) For the kick start to be in neutral and yet still turn the rear wheel there has to be unwanted stiction somewhere in the gear circuit. The Layshaft 4th (Kickstart) should spin freely on the Layshaft. If it is binding this will turn the 4th Layshaft which in turn will spin the gearbox sprocket.

2) Still in neutral, operating the kick start turns Layshaft 4th and Mainshaft 4th. If the bushes inside the Layshaft 1st (output) gear are binding with the Mainshaft then both will turn and try and rotate the rear wheel.

3) The kickstart shaft bush/bearing is binding on the Layshaft. Check the shaft hole is concentric.

4) Most unlikely but possible.....one of the drive chains is far too tight and causing stiction between the gearbox Mainshaft and Output shafts.  A bit like (2) above.

Something obvious but often not checked. See if the ither shaft is bent. I have seen layshaft with only a small run out causing similar problems.

Paul

Slacken the gearbox mounting bolts and recheck, it most probably distorted a little in use. 

Sometimes a fresh pair of eyes  will spot something, where abouts are you? , there may be someone near.

The early AMC box uses a different shaft and spring and inner cover to the later box ,could you have a mixture somewhere?.

Is the kick-start pawl too wide? Or the wrong way round? Jamming somehow?

Primary chain tension possibly 

The other thing is to check the clutch is not done up with the inside abutting the sleeve gear. If the clutch or shims used to fit the clutch touch the end of the sleeve gear this will lock the sleeve gear and the mainshaft together. If you are using the original clutch centre is the brazed in washer still in the bottom of the spline, if this is missing then the clutch will be able to sit too far inboard. 

I’ve used Dave Coates for gearbox and clutch working the past, he might be worth a ring. I think he charges £50-60 to rebuild a box plus any parts. He has a lot of experience/knowledge. He rebuilds boxes and clutches for the pre unit Scrambles bikes but is in the SE I think. He certainly used to go to Shelton and Kempton.

dan 

The kick start operates on the Layshaft. This turns the 4th Layshaft Gear which then rotates the Output Sleeve Gear to which the sprocket is bolted. In Neutral...... for the Layshaft to turn the Mainshaft / Clutch either the clutch is binding on / against the Output Sleeve Gear or somewhere in the gear train a set of gears turned by the Layshaft is trying to turn the Mainshaft.  Possibly due to the Mainshaft 2nd or Layshaft 3rd gear pairing dogs engaging when they shouldn't or a bush in either of these gears being too tight.

One other possibility being that ........what you think is neutral is actually a selected gear???

There is usually some small amount of clutch drag on Norton Singles.  When they are started on the rear stand with the rear wheel off the ground, the rear wheel almost always turns..or even spins...and a touch on the brake pedal confirms it really is in neutral before pushing it off the stand.  The Dommie would no doubt be exactly the same if it had a rear stand.

Not sure if this applies to your problem:

I note you have a diaphragm clutch fitted [belt drive].  When I fitted a belt drive to my 650ss I had a similar problem.  When tightening up the Clutch centre nut the gearbox/back wheel locked up.  I had to have 1mm machined off the back of the diaphragm clutch body  to free everything up.  Is this a new Belt Drive kit?

Rather late to the party - but I had a similar issue on a laydown box and had it apart many times. The problem turned out to be a new layshaft bush in the kickstart shaft that had been bored crooked.  What lit the lightbulb was that if I substituted the K/S shaft with one where the bush was worn out, it was fine.  Ended up replacing the bush and having it very accurately bored and reamed in a lathe with a 4 jaw chuck.  Worked fine after that.

Hi Alistair

Did you sort the problem? Missed this discussion, just found it.

I had exact problem with my 650ss, 4yrs ago after fitting

Kick-start shaft and new spring. Then another new Kick-start shaft.

Same problem. Both from Norton Dealers.

My bike has original chain primary.

 Answer? Correctly checking end-float on Kick-start shaft 

Then shelling out £30 + on an expanding reamer to remove

the tiniest sliver of material from outer over Kick-start bush.

Tim