Gearbox Layshaft Issue?

nomadwarmachine · Oct 5, 2020

1974 Commando Mk2 w/recently rebuilt gearbox. It has recently developed a strange -- and worrying issue -- whereby the kickstarter will effectively lock up on the compression stroke when starting. I can put my full 170 lbs on top of the starter and it will push through but eventually stick in place, gradually easing after a few seconds and pushing through. However, if I kick it under normal force, it will lock with a loud sound that sounds like there is real interference internal to the gearbox (sound is like hitting an automotive starter when the car is running). If I take the plugs out, the transmission turns easily and smoothly in neutral.

I thought that I might have a bad Boyer, so I swapped for a Pazon and made sure I had a fully charged battery. It is static timed at exactly 31 degrees BTDC. Makes no difference. In neutral, the kickstart still offers plenty of resistance on the compression stroke and if I jump on the kickstarter it will frequently make the "krrang" noise upon locking. If I then pull back up, I can push through again but this makes it VERY difficult to get started.

Could this be a symptom of maladjusted layshaft end float? In the course of stripping the gearbox, I noted that I had an original "Made in Portugal" ball bearing that has since been replaced with a proper roller. The current end float on the layshaft is about 1/8" -- realize that this is a lot but I have not had any trouble with it disengaging from 1st on hard acceleration. Just this strange problem that has become progressively worse. Could the issue I have with the kickstarer locking/noise in neutral (w/ignition on) be tied to excessive end float? If not, any other ideas? Motor runs like a top once started.

concours · Oct 6, 2020

nomadwarmachine said:
1974 Commando Mk2 w/recently rebuilt gearbox. It has recently developed a strange -- and worrying issue -- whereby the kickstarter will effectively lock up on the compression stroke when starting. I can put my full 170 lbs on top of the starter and it will push through but eventually stick in place, gradually easing after a few seconds and pushing through. However, if I kick it under normal force, it will lock with a loud sound that sounds like there is real interference internal to the gearbox (sound is like hitting an automotive starter when the car is running). If I take the plugs out, the transmission turns easily and smoothly in neutral.

I thought that I might have a bad Boyer, so I swapped for a Pazon and made sure I had a fully charged battery. It is static timed at exactly 31 degrees BTDC. Makes no difference. In neutral, the kickstart still offers plenty of resistance on the compression stroke and if I jump on the kickstarter it will frequently make the "krrang" noise upon locking. If I then pull back up, I can push through again but this makes it VERY difficult to get started.

Could this be a symptom of maladjusted layshaft end float? In the course of stripping the gearbox, I noted that I had an original "Made in Portugal" ball bearing that has since been replaced with a proper roller. The current end float on the layshaft is about 1/8" -- realize that this is a lot but I have not had any trouble with it disengaging from 1st on hard acceleration. Just this strange problem that has become progressively worse. Could the issue I have with the kickstarer locking/noise in neutral (w/ignition on) be tied to excessive end float? If not, any other ideas? Motor runs like a top once started.

1/8”......
You answered the question.

kommando · Oct 6, 2020

Plus check the kickstart pawl for wear or the slot it fits into and the matching teeth inside 1st gear.

NickZ · Oct 6, 2020

It could be that the kick start shaft is able to slide over the top of the pawl plate that is on the inside of the inner cover. I don't think reducing end play by shimming the kickstart shaft will eliminate this, because the shimming just makes it so the shaft can't travel down as far, but it still can go as far as it did before toward the top of the pawl plate. IMO a better fix for this would be to raise the pawl plate by putting a shim under it. But that involves removing and replacing the rivet that attaches the pawl plate to the inner cover.

Torontonian · Oct 6, 2020

Always the shimming with Brit Bikes.

nomadwarmachine · Oct 7, 2020

Always the shimming with these...

ashman · Oct 8, 2020

Norton's were built with endplay lol I be more looking at the kickstart area inside end of the KS shaft, pawl, and KS gear something is not right but its not a hard job to pull the covers off and do a full inspection and replace anything that looks not right.

Ashley

concours · Oct 10, 2020

ashman said:
Norton's were built with endplay lol I be more looking at the kickstart area inside end of the KS shaft, pawl, and KS gear something is not right but its not a hard job to pull the covers off and do a full inspection and replace anything that looks not right.

Ashley

yes, but while originally the kicker end play didn’t matter, the OP changed to a roller type, the end play is what locates the layshaft.

nomadwarmachine · Oct 10, 2020

Opening the gearbox this afternoon. Will report back on my findings.

nomadwarmachine · Oct 10, 2020

Measured end float on the KS shaft with the inner cover on. .045"

NickZ · Oct 10, 2020

I don't believe that is your problem.
You need to remove the inner cover to inspect the pawl, 1st layshaft gear and the plates riveted to the inside of the inner cover.

nomadwarmachine · Oct 10, 2020

I have everything out, including the layshaft. The gears look to be in excellent shape and there is no obvious sign of any damage, nor any residue in the bottom of the shell.

What exactly should I be looking for in terms of wear in the pawl, layshaft gear and rivet on the inner cover? I will try to post a photo of all of these.

Changaroo · Oct 11, 2020

Could it be the a loose clutch nut allowing the clutch to jam on the primary cover and then with all your weight on the kickstart eventually forcing it through? With the plugs removed, there is little resistance, with everything turning over easily and not forcing the clutch to jam?

NickZ · Oct 11, 2020

nomadwarmachine said:
What exactly should I be looking for in terms of wear in the pawl, layshaft gear and rivet on the inner cover? I will try to post a photo of all of these.

You would be looking for wear or damage on the end of the pawl where it engages the ratchet teeth on the inside of 1st layshaft gear, wear or damage to those teeth, and wear or damage to the plates, including signs that the pawl or kickstart flange has been coming over the top of those plates. I have a photo of this last condition:

nomadwarmachine · Oct 11, 2020

Enclosing pictures of the 0.45" float on the KS (w/inner cover installed) as well as details of the KS shaft, gear, and the inner cover. There was a 0.20" iso shim (not shown) already behind the KS shaft, increasing the total float to 0.65". A couple of 0.30" shims should take up the slack.

The good news is that I did not see any obvious signs of wear or damage inside the shell. No flakes of metal or shavings. All of the bushings were replaced 200 miles ago when the gearbox was rebuilt.

Cannot see any clear damage to the inner cover, pawl, or KS shaft that would lead to the strange locking I get when kicking the starter hard. Also pulled the clutch inspection cover on the primary side. With the plugs out, the gearbox turns fully and freely -- no issue there whatsoever.

kerinorton · Oct 11, 2020

When I rebuilt my g/box [ using the parallel roller instead of the ball bearing ] there would have been 80 thou [ 2mm ] end float and I had [ and still have ] no problems.

BTW. The original ball bearing everyone keeps going on about, is a slip fit over the layshaft, so it can't control endfloat.

ashman · Oct 11, 2020

Everything looks fine there, could it just be a bit of compression lock that cause it if you kick the bike over sometimes it does that when you go to kick it depends where the pistons are sitting when you go to kick it and of course it does make a sound when it does it, just the gears taking up the slack, mine has done it a few times in its life and can be a pain in the kick leg when it does it.

Ashley

kerinorton · Oct 11, 2020

I agree with Ashman. Just forgot to mention it.

nomadwarmachine · Oct 11, 2020

What causes compression lock and how would you go about resolving? It does that every time I start the bike from cold. Less so when warm.

ashman · Oct 12, 2020

Do you get your pistons up to near top dead before kicking it, not knowing how or what you do before you give it a big kick, not much you can do about it if not kicking your bike right, I been kicking mine for over 45 years so have my kicking down pat but sometimes it bites me unexpectedly, but my Norton is a one kick start, one big kick for the first start of the day and after that it fires up on half a swing on the kicker all day.

Ashley

Gearbox Layshaft Issue?

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