Good News, Bad News, and Really Bad News!

The Good News:

I was only going 5 miles an hour in the Home Depot parking lot on my Mark III when it happened about an hour ago - my rear wheel completely locked up, skidding me to a stop. Sure would not have been pretty just 2 minutes later, when I would have been going 50 MPH.



The Bad News:

It's not a stuck brake. The problem is in the gearbox, as the kick start lever is either locked completely or really hard to move (in neutral). It has been alternating between both states as I have dragged/lifted the bike onto a truck and into my yard. There were a few occasional clicks from the gearbox too, and at one point the kick lever was moving with the rear wheel. I guess the other good news is that there isn't a rod sticking out of the engine case. (and there was no accompanying sound effects when this happened, just the skidding of the rear tire).


The Really Bad News:

I'm sure that's what I'll see on the inside of the gearbox. But not today. Damn - the bike has been riding so sweetly the last couple of thousand miles!!

Side Note (I assume) - when I started the bike to go out for my ride today, I noticed the tach was not spinning - dead and motionless. I'm sure there's no connection, but thought I would mention it, just in case .......

The not so bad news (potential) - you've got a done-in layshaft bearing and it hasn't trashed anything but itself so far.

The really great news (potential) - as you said, it happened in a parking lot, and not on the freeway. You're at minimum up one pair of undershorts, at maximum, you're alive and so's the bike. In an alternative universe, that bearing (if that's the problem) gave out at 70 MPH, leaving a long skid mark, a trashed bike, and a grieving family and friends.

Here's to your good luck so far (I think) and hoping it continues when you open the gearbox.

Sounds like good news to me. You must be around 12000 miles on the bike. If your lucky you will just need a new heavy duty layshaft bearing.
When my MK3 did it many years ago I was just pulling into traffic on the Interstate. It wasn't pretty. Jim

Classic lay shaft bearing as mentioned. Glad you didn't loose teeth, in your own head. Do give attention to check shaft run out and dogs and bush slack while in there. Gave ya a nice upright straight steering skewed ride to a stop I'll bet.

Hopefully the 4 th gear pair havent been damaged as theres bound to have been bits of bearing go between the teeth. You'll have to have a close look at them. Ive just bought the 4 th gear pair from Mick Hemming, 36 & 77 pound plus freight. Looking at information on bearing manufacturers web sites, rollers have double the load rating, 29 Kn compared to 14 kn of the ball.The roller I purchased is Japanese FBJ NJ203EM C3 and has a brass cage.
By the way, thats a nice looking Commando.
Foxy

My "spun-a-Layshaft-bearing" story:

1973 850, I was leaving work and as I got into third gear the Universe went NUTS, the rear wheel locked up, the front wheel made a fast and ugly trip back to the pavement (hey, I was 18 and the Commando was FUN to pound on!). I ended up having the 'box rebuilt 7 times in 9 years and it was not until years after I sold the bike that I determined I had pulled the Case out of square and the rebuilds were just hiding the symptoms (for a while, anyway). That day (pretty much) ended my Wheelie-career, surprises on one wheel SUCK!

As slow as you were going I would not worry too much.

Unclviny

Well this makes me paranoid. Is there a way to test this before it goes bad? My tranny hasn't been messy with in 20+K miles. Would hate to be going down the road with the wife on back and have this happen especially if it is something that is prone to go after 12K.

No way to test without opening up the gearbox and looking at the bearing, an early sign is the kickstart dropping downwards on its own as you drive along but not always. I got that sign when mine went, inside there was no damage to the gears but a few split balls in the bottom showed they had been crunched up in between the gears :shock: . Mileage was about 12 to 15K.

The bearing does not fail but the cage does, the balls are free then to bunch up on one side and the bearing inner moves to one side leaving the balls to make an exit for freedom.

Fix is a roller bearing or a ball bearing with an uprated cage.

I'm glad I had the oporetuniuty to replace the layshaft bearings before I started riding my bike, as I was restoring the bike. I used the NJ roller and you need to shim the layshaft tail, where it goes into the kick starter extension. You can use the shims from your isolastics. For what it is worth it really is not such a massive job to just replace the bearing, sure beats the possible alternative?

Glad you had a lucky escape!
Rich

Is there a part number and brand that is better and is there a replacement that doesn't require extra shims?

The replacement bearing from Andover Norton is a #06 7710 . It is a roller bearing number NJ205e.tvp2.c3. It is a direct replacement and requires no shimming. The roller bearing replacement will last a long time. A good ball bearing will last pretty good. The only bearing that always failed around 12 thousand miles was the original bearing in the MK3. The original ball bearing in other Commandos usually lasted longer if the oil was kept clean.

These mileage references are very interesting to me. My MK III came to me just short of being a basket case. It was put together with parts from several bikes, including earlier models. Since the clocks were of the green globe vintage, I have no idea how many miles are on the bike although the engine runs strong. Earlier this year, I found my kick starter moving rearward on accelleration so I had the lay shaft bearings updated. COULD this mean that this bike has somewhere around 12K on it, or is that too big a leap in logic?

COULD this mean that this bike has somewhere around 12K on it, or is that too big a leap in logic?

The cause of this issue coming to surface was the introduction of the 850, the gearing was taller plus the engine gave extra torque which increased the loading on the gearbox. That plus a batch of duff bearings from Portugal made it a epidemic. Mine was on a 850 MK2a and had the Portugese bearing, so its not just on the MK3's.

The Portuguese bearings were used before the MK3 and failure of the bearing was a problem but not nearly as regular as on the MK3. Pretty much every MK3 I have seen was around 12k when they failed. When I called TC Christianson in 82 when mine failed his remark was "oh you must have around 12 thousand on it"
Anymore I won't ride a Norton without knowing what is in there for a layshaft bearing. Jim

Ok, paranoia now.

I have a 73 MKII 850 that is all original, 5k miles. So the bearing can't be too expensive and I haven't check the manual yet, Is it a big deal to replace? Is it on the outboard cover or on the primary side? If the outboard side sounds like it would be a fairly easy fix.

Either way, I had better get that corrected, bike is to original and to nice to lay down from something like that.

Crap, now I'll be worried my whole trip to barber and back.

I see a couple of references to the 12,000 mile mark as a potential failure point for lay shaft bearings.

My Mark III just ticked over 21,000 miles, and had 14,000 when I bought it 3 years ago. I don't think the previous owner did anything to the gearbox, so my bike and its lay shaft bearing made it a long way past the 12,000 mile point.

The best part, though, is that it failed when I was just pulling out of a parking spot in a parking lot, in first gear, and going 5 miles per hour.

Failure a mile earlier or a mile later would have been downright ugly.

My wife is more shook up about this than I am, since I have more than one bike and ride about 15,000 miles a year. She thinks this is a motorcycle issue, as opposed to a 35 year old Brit bike issue. I am more concerned about the down time, hassle and cost to get the Commando back in action.

Oh well.... ride on. What else can you do?

It's a full strip to replace the bearing as it is deep in the case. The NOC Service notes stated that it was most likely to occur with larger (greater than 21t) gearbox sprockets.

It has been stated on the forum a number of times but you'll find no experienced long-term owners giving you any advice other than 'replace it' Once it's sorted then you'll never need to do it again.

Failure is so potentially disastrous that the only sensible course id to do it as soon as possible. In the meantime, watch your kick start lever like a hawk for signs of flinging back.

I expect we'll be seeing some photographs soon of what goes on.

If Pkeithkelly's has only trashed the bearing then it's an easy job over a weekend.

1973 850, I was leaving work and as I got into third gear the Universe went NUTS, the rear wheel locked up, the front wheel made a fast and ugly trip back to the pavement (hey, I was 18 and the Commando was FUN to pound on!). I ended up having the 'box rebuilt 7 times in 9 years and it was not until years after I sold the bike that I determined I had pulled the Case out of square and the rebuilds were just hiding the symptoms (for a while, anyway). That day (pretty much) ended my Wheelie-career, surprises on one wheel SUCK!

Click to expand...

Unclviny and me have similar events with identical conclusions. Can not go by mileage at all as a single event like to tight a primary drive or an item breaks in gearbox - can mean whole power train distorted - cases to shafts to bearings and cogs and control linkages. Trixie Combat I'm about to re-do engine on, locked up instantly at 50 mph cruise so I'm pensive as hell the drive train may catch me out during mere break in interval. I think re-used rod bolt let go, as one had corroded fracture face the other did not.

It can cost nearly $1000 to get a really broke bike back home form out of the way locations. A weekend to motel while locating a truck that maybe 10's of miles away and way over size but only thing available. Its about a wash if trying to repair major stuff far from home. Moteling-camping awaiting parts and shops to fix. Too often climate dictates and inside job.

Travel long and safe in scared confidence.
hobot

PKK,
I'm awaiting my 932's back from Lunds.
Then I am doing the layshaft bearing as well.
I have a 72 combat w/ now 9900 miles on the clock.
I have no reason knowing the history of this bike doubting the miles are true/correct.
This being said and all the failures reported no sense ruining a great bike over a $5.00 bearing.
I contacted a local bearing distributor and got an exact replacement 6203 c-3 for a little over $5.00.
I have not experienced bearing failure YET!!!
You can go roller or ball type bearing.
It's not a big job to shim the roller bearings end play per this forum.
Just avoid binding of the shaft and kickerbush is all you are trying to accomplish there.
I'm a Sunday solo rider so by the time the bike has an additional 12,000 miles it may very well be my sons.
I went OEM ball bearing w/ stainless steel cage as thats what was called for.
I don't race so I don't need a heavy duty mk 19 bullet proof roller type w/ kevlar reinforced jacket.
It's you call check forum for how to do it its covered.
Oldbritts.com has an excellent how to in the tech section of their site
I'm over do as well so no sense taking a chance. :shock:
Marshal