Gearbox

Layshaft bearing drive side gone. Replace with 06-7710 roller bearing. Check state of 04-0146 bush in kickstart shaft. Do not continue riding the bike unless you want to buy a new gearbox shell.

Hi Barry

I agree with Joe, its just as well you put the bike in a van, the layshaft bearing fitted into the gearbox case is worn and needs replacement. The play in the layshaft grips the kickstart shaft under load and pulls it backwards (one end of the layshaft runs inside the kickstart shaft). The bearing can break up causing much damage, itmust bereplaced withthe stronger roller bearing.

Alan

Whilst in there get a re-build kit and do all the bearings, seals and bushes. You'll be surprised that though the bushes feel fine, when tried against new ones it is some difference, it will also transform your gearbox. I was used to my old box and had same problem - bit the bullet and done it, but it felt 10x better when done. If it is a MKIII the gearbox will come out through the right mounting plate - just a bit fiddly though.

Barry, Feeling better? I got the flu New years eve and still getting over it! The box will come out as per Mk3 but if you have a 72 (Combat) the n/s case breatherstops the box from rotating backwards until the mounting lugs align with the cradle cutouts. You need to remove the three rear engine studs and pull the cradle, box and swingarm assy to the rear. You will then have enough space to work. If you remove the breather assy as well that makes it easier also.

Ken, Had similar issues myself several years ago. Also tried the 'Iso' shim trick but it made little difference. My problem was the k/s moving in 1st on brisk takeoffs. It wasn't the lay bearing as it already had a roller fitted. After several rebuilds and finally with the same HD ball bearing you have I noticed witness marks on the layshaft 2nd gear dogs and k/s shaft face which had been contacting the end of the k/s shaft. Where these 2nd gear dogs project thru the lay 1st gear the end face of the k/s is recessed. I had to shim1st gear away from the k/s by appx 020" and that solved the problem. If you study the gearbox pics on Old Britts site under Tech articles - How gearbox works it might help. Why I had to do this I don't know, just unlucky with tolerances I guess. Certainly never heard of anyone else having to do it. While you have end play with your k/s there may be enough movement with gears to bind under load. Just an idea.

http://www.oldbritts.com/ob_start.html

I swopped my layshaft ball bearing for a roller and the box lost its sweet change, no idea why, next time i'm in there i'll go back to a ball bearing which is ok on a Dommy.

When I rebuilt mine, I noticed the lateral play in the kickstart shaft seemed excessive but still enabled the pawl to engage correctly, so I did not fit any shims to correct and it works fine. I replaced the layshaft original roller bearing with a new roller bearing that was in the kit. Kick start works fine. I had no markings that suggested that anything was wrong or needed shimming so just rebuilt.Personally, I would remove the shim and rebuild it providing their are no serious marks in places that you would not expect to find it.