Will riding my 1971 commando today I noticed my kick start lever bouncing up and down. I started to slow down and my rear wheel locked up and I skided to a stop. Could not get the trans out of gear and the kick start arm was very hard to move up or down. Pulling in the clutch lever would not free the wheel up. I'm assuming something in the trans went wrong. Any ideas?
transmission set up
- Thread starter gwallen
- Start date
- Status
- Joined
- Dec 28, 2009
- Messages
- 5,427
Well you survived layshaft bearing lockup , good , you're alive to live another day.. now tear into that gearbox and fit a new roller type bearing . You will need a heat gun for the box and a freezer for the bearing itself. Lots of info here on how to do it. You don't even need to pull the primary and gearbox. You can do it all just pulling the 2 gearbox covers. :wink:
- Joined
- Jan 1, 2005
- Messages
- 195
If your luck holds out everything will go as planned. When my lay shaft bearing went out one of the balls tried to escape through the side of the case. The entire box had to be removed and the wound welded over. Hasn't leaked a drop from that spot in many years since.
Ride On
Dave
Ride On
Dave
You Were lucky it wasn't at speed. I had my rear wheel lock the other day (not gearbox)at 30mph, not funny. Have a look at Old Britts gearbox pages, really useful in case the manual is not clear enough....http://www.oldbritts.com/gearbox_a.html
- Joined
- Apr 21, 2015
- Messages
- 322
Have often wondered how many have died due to Commando gearbox failure........ According to the ex NVT friends I asked it was not an uncommon problem on Commandos and the reasons they gave for it were...
1 the rediculously increased rotating unbalanced weight of the Commando so called clutches compared to earlier clutches....especially the bronze plated versions.....according to people such as Mr Irving a gearbox mounted multiplate clutch is suppossed to possess the LIGHTEST rotating weight possible rather than the heaviest as AMC / NVT fitted to Commando models
2 the reduced primary ratio employed on Commandos which reduced the gearbox rpm compared to Atlas and 650 models which simply increased the amount of torque being shoved through the box.
Mre Peter Williams very polite thoughts on use of the gearbox for Commando models are given in his book......Some of us can still remember how the things rarely completed a lap of The Island before failing... till Mr Williams added a PROPERLY mounted mainshaft support bearing behind the clutch to stop the mainshaft distorting resulting in the gears being incorrectly meshed along with a few other little modifications to protect his arse when racing the lumps............
Never thought about such things? Ever noticed how the Commando gear set bares an uncanny resemblence to the Sturmy Archer 4 speed box design on the early 1930s which was designed for use on motor cycles probably producing no more than 25 ft lb of grunt at the crank and not the 45-55 odd ft lb of a Commando motor........ There is a sectionised picture of the original Sturmy Archer 4 speed box on the web......... when Sturmy Archer ceased making them Norton had them manufactured by Burman and later played with them till they ended up being known as the AMC Norton box. The history of the box is given in one part of 'The Norton Story' published in Motor Cycle Sport many years ago. from memory the January 1972 edition.
1 the rediculously increased rotating unbalanced weight of the Commando so called clutches compared to earlier clutches....especially the bronze plated versions.....according to people such as Mr Irving a gearbox mounted multiplate clutch is suppossed to possess the LIGHTEST rotating weight possible rather than the heaviest as AMC / NVT fitted to Commando models
2 the reduced primary ratio employed on Commandos which reduced the gearbox rpm compared to Atlas and 650 models which simply increased the amount of torque being shoved through the box.
Mre Peter Williams very polite thoughts on use of the gearbox for Commando models are given in his book......Some of us can still remember how the things rarely completed a lap of The Island before failing... till Mr Williams added a PROPERLY mounted mainshaft support bearing behind the clutch to stop the mainshaft distorting resulting in the gears being incorrectly meshed along with a few other little modifications to protect his arse when racing the lumps............
Never thought about such things? Ever noticed how the Commando gear set bares an uncanny resemblence to the Sturmy Archer 4 speed box design on the early 1930s which was designed for use on motor cycles probably producing no more than 25 ft lb of grunt at the crank and not the 45-55 odd ft lb of a Commando motor........ There is a sectionised picture of the original Sturmy Archer 4 speed box on the web......... when Sturmy Archer ceased making them Norton had them manufactured by Burman and later played with them till they ended up being known as the AMC Norton box. The history of the box is given in one part of 'The Norton Story' published in Motor Cycle Sport many years ago. from memory the January 1972 edition.
J. M. Leadbeater said:
Just to be clear here, this is not a Norton Commando Gearbox. It is an AMC gearbox and has been around in one form or another long before Commando's were ever thought of. Associated Motor Cycles has parented many fine motorcycles, AJS and Matchless, and trhe gearbax has been employed on the Model 50 since LAB only knows.
I am not saying your wrong with your concepts, you just need to lay blame where it belongs.
- Joined
- Nov 20, 2004
- Messages
- 20,423
Hopefully, gwallen's experience will serve as another timely reminder to all those Commando owners who haven't as-yet got around to checking if their Commando's gearbox still has a standard 6203 drive-side ball bearing!
The next person to experience a layshaft bearing failure (which can happen with little or no warning) may not be so lucky and we may only get to hear about the lucky ones so make it your priority winter "to-do" job to inspect and, if necessary, replace any steel or brass cage 6203 drive side layshaft bearing with either the NJ203E roller bearing upgrade (Norton part 06-7710/NM18337) or FAG 6203 TB ball bearing.
There are a significant number of threads discussing this and how to change the bearing already but-as always, if further help or advice on how to carry out this job is required then-just ask, however here is a good starting point: http://www.doov.com/apps/nortoncompanio ... ng-upgrade
The next person to experience a layshaft bearing failure (which can happen with little or no warning) may not be so lucky and we may only get to hear about the lucky ones so make it your priority winter "to-do" job to inspect and, if necessary, replace any steel or brass cage 6203 drive side layshaft bearing with either the NJ203E roller bearing upgrade (Norton part 06-7710/NM18337) or FAG 6203 TB ball bearing.
There are a significant number of threads discussing this and how to change the bearing already but-as always, if further help or advice on how to carry out this job is required then-just ask, however here is a good starting point: http://www.doov.com/apps/nortoncompanio ... ng-upgrade
- Joined
- Feb 10, 2009
- Messages
- 2,978
J. M. Leadbeater said:
Did fitting a stronger bearing not occur to your deep-thinking friends?
L.A.B. said:
Thank you everyone for your expert advice. I know the good Lord was riding with me yesterday as just before the break down I was really puting the old commando to the test. At the last moment I decided to take a turn and go a way home I don't usually take and as a result I was going maybe 30 mph. Skidded to a halt and that was it.
ashman
VIP MEMBER
- Joined
- Jul 11, 2010
- Messages
- 6,006
J. M. Leadbeater said:
Well how come it doesn't blow up after the orginal bearing has been replaced, mine blew at 12Ks (3 years on the road) when I brought it new and had to replace the bearing, since then I am still running the same bearing that was replaced (37 years now) without any more problems with my gearbox, my Norton has over 140,000 miles on it now, the only other time my gearbox has been pulled apart is to replace the kickstart pawl (4 times now and one kickstart gear) I also still running my orginal bronze clutch plates, if every thing is ajusted right (primary and rear chain) then there should not be no stress on the gearbox, maybe I have just been lucky.
Ashley
- Joined
- Dec 28, 2009
- Messages
- 5,427
Huge mileage. Obviously it was replaced with a higher quality bearing way back when. Just for fun pull apart the tranny and tell us the bearing make and numbers before you install a roller equivalent seeing as you are now in there anyways. 
- Joined
- May 7, 2005
- Messages
- 7,163
Its the cage that holds the balls in place that goes first, this allows the balls to drop to one side of the bearing so the inner then cocks to one side and the balls then fall out, its the loose balls than then get stuck between the gears and cause the lock up. So a ball bearing with a good cage will last probably as long as the roller. After my failure which was not with a lockup I found several 1/2 balls in the bottom of the gearbox, they had been minced by the gears instead of jamming. The bearing I took out was an FAG Portuguese bearing and I replaced it with a Roller. My symptoms started with the kickstart turning on acceleration and then within 2 miles a bad gearchange, dropped off the passenger at a bus stop, stuck it into 4th and drove 10 miles through traffic.
- Joined
- Dec 28, 2009
- Messages
- 5,427
Mine locked up in traffic with cars honking up my derriere. Limped home in 2 nd gear. I knew something was up the day before as there was an occasional "tick" sound followed by the kicker moving about on it's own. But I was young and busy and it was summer and I had no tools to take it apart midsummer. :roll:
- Joined
- Nov 12, 2015
- Messages
- 1
I've seen my share of Norton gearboxes- the roller layshaft bearing generally keeps the unit together for a street bike. Any ball bearing replacement should be tougher than the original Portugese one. I would imagine that the latest crop of Chinese bearings would be worse than the Portugese ones, from my experience. So, put in a roller and be done with it. And yes, the weak link in the box is the mainshaft (once the layshaft bearing is sorted out)- they get beat to death by the clutch assembly, any slight internal misalignment from worn bushings and/or gears, and age does take its toll. I had one walk the sleeve bushings out of the top gear set and got to haul the bike via trailer, as the clutch centre got reamed out. The mainshaft was bowed, so it was a crash course in AMC gearbox. That bike had about 13K on it (73 Combat Roadster), and I had not looked inside the 'box up to that point. I've since built a bunch of them (AMC boxes) and had no real problems- even on the race bikes (80's WERA and AHRMA circuits). If you've got a machine with an unverifiable history, or you've been blasting around on it for a while (and can't remember when/if you looked at the gearbox) it is cheap insurance to pull the box down and make sure all the bushes and bearings and shafts are in spec. It beats walking!
- Joined
- Dec 28, 2009
- Messages
- 5,427
As for bushes always critically replace the sleeve mainshaft ones(2) and also the delicate 1 st gear bush. The others last a surprisingly long time. That Redline Shockproof oil is so great. 
Nater_Potater
VIP MEMBER
- Joined
- Apr 7, 2013
- Messages
- 1,342
Walking, or being smeared all over the highway. Most of my traveling around here is over 50 mph, with a big chunk of that at 65 in heavy traffic. At over 17,000 miles on the clock, this is the winter for gearbox scrutiny. Besides, the head has to come off for bad exhaust threads. Gwallen, I'm so glad to hear you survived yours unscathed!motorcritter said:
Nathan
- Status
