Lay Shaft

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My brother has a 74 Commando. He said he is going to replace the lay shaft. He heard that if the lay shaft breaks, very bad things happen. I am still trying to figure out a number of things on my MK III, so this concerns me. First, what is a lay shaft? How often do they go bad? How can I tell if mine is marginal?

I will say thanks in advance for the input I know will be coming.
 

ILLF8ED

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Re: Lay Shaft bearing

The layshaft bearing is a known weak point. The indication that it's going or gone is the kick start level drops back when you accelerate. There is a roller replacement for the ball bearing Norton put in originally that solves the problem. If you're concerned you will need to tear into the gearbox to see if you have a roller or ball bearing. It's on the drive side embedded in the gearbox case (smaller bearing - the large one is the main shaft bearing).

David
 
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I replaced this ball with an SKF roller.
You need to strip the box to do this.
I would use illf8ed's info....if and when you see the kickstart rotating anticlockwise (down) on its own during hard acceleration from a standing start then sort it.
If you log into Colarado Norton Works site Matt has given a close up view of this bearing which gives the code.....thanks Matt.
Otherwise The NOC will supply this information.
Stuart.
 

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bigstu said:
....if and when you see the kickstart rotating anticlockwise (down) on its own during hard acceleration from a standing start then sort it.

The time to sort the layshaft bearing is: NOW!

I don't recommend anyone wait until the box starts to exhibit symptoms of the bearing breaking up, as that may well end up being too late for both gearbox and rider if the gearbox locks solid at speed!

If the layshaft bearing type is unknown,-then it needs checking at the earliest opportunity. Many layshaft ball bearings will already have been changed for the roller bearing, however if the layshaft bearing type is unknown, then I strongly suggest all Commando owners to check it as soon as it is reasonably convenient for them to do so.

The replacement layshaft drive side roller bearing is the NJ203(C3) with single lipped inner spool, the lip of which, must fit against the layshaft high gear. There have been some instances where owners have found the N203 roller in their gearbox which has no inner spool lips, but do not use that type of bearing.


There is however, a second option of a high grade FAG6203TB phenolic cage ball bearing, and Mick Hemmings recommends this type of bearing over the roller, although the roller bearings give no trouble in service.
 
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Hi Cal,
Yes, if your layshaft broke that would indeed be a very bad thing. Personally, I have never heard of one breaking, but, I'm sure that somewhere somehow someone has managed it.
The layshaft ball bearing to roller bearing replacement that others have mentioned can be done with the transmission case still in the bike. Its been a few years since I converted mine, but, if I remember correctly I did not even have to disassemble the primary drive (IE the mainshaft was left in place. I heated the case with an electric heat gun, then used a slide hammer to pull the old ball bearing out, heated the case again and tapped in the new roller bearing, which was a FAG bearing part number NJ203E.TVP2 Not exactly a project for the mechanically challenged, but, doable at home with basic tools.

GB
 
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Hi LAB
Of course you are correct, a failure would be a bad thing, but it is a bit of a job to sort.
I just ran to Switzerland and back with a guy who had a slightly rotating kickshaft. A distance of 1600 miles.
It didn't fail...
There must be many Commando owners running without this bearing mod....should they all strip their box now?
Callingbird's brother is not suggesting he has problems, but if he is thinking of replacing the layshaft he should do the bearing mod., you are right. I agree.
Stu
 
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geo46er said:
Hi Cal,
Yes, if your layshaft broke that would indeed be a very bad thing. Personally, I have never heard of one breaking, but, I'm sure that somewhere somehow someone has managed it.
The layshaft ball bearing to roller bearing replacement that others have mentioned can be done with the transmission case still in the bike. Its been a few years since I converted mine, but, if I remember correctly I did not even have to disassemble the primary drive (IE the mainshaft was left in place. I heated the case with an electric heat gun, then used a slide hammer to pull the old ball bearing out, heated the case again and tapped in the new roller bearing, which was a FAG bearing part number NJ203E.TVP2 Not exactly a project for the mechanically challenged, but, doable at home with basic tools.

GB

I broke one on my "S" in the seventies when I went drag racing and I rode it home :!: I was young and carefree (read dumb) no problems at all on the way home. When I took the box apart, the layshaft was cleanly cut at the first gear end.

Jean
 

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bigstu said:
a failure would be a bad thing, but it is a bit of a job to sort.

I wouldn't consider it to be that big a job-but that's just me, others might do? Sorting it after a failure might be a much bigger job!



bigstu said:
I just ran to Switzerland and back with a guy who had a slightly rotating kickshaft. A distance of 1600 miles.
It didn't fail...

Then either he was extremely lucky, or, the problem may not actually have been due to the D/S bearing cage breaking up? Possibly the lay shaft was picking up inside the T/S bearing, or perhaps it was due to a lack of end play between the layshaft and kickstart shaft,-I don't know?

But I do know others have said that the bearing broke up with little or no warning, Debbie said this in a previous thread:
debbie said:
The layshaft bearing on the '73 850 that I owned back in the day failed with no warning whatsoever. The gearbox just locked up while I was riding down the highway at 60 mph. Fortunately there was no traffic behind me and I was able to skid to a stop without getting run over.

bigstu said:
There must be many Commando owners running without this bearing mod....should they all strip their box now?

It should at least be on their "to do" list, and "do earlier rather than later" in my opinion?
 
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Thanks for all the input. I will have to sort this out. I bought the bike last year and have found it to have been bits from several bikes. With that in mind, I have no idea if this has been done or not. I haven't seen any movement in the kick start lever, but apparently that may not mean much. I am also not sure if I am ready to tear into the gear box.

I'll have to ponder a solution to this one.

Thanks again
 
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Hi Gang:
Get rid of that bearing.It happened to me years ago.Lucky for me it was 30 mph.You automatically grab the clutch,but with no luck.It is locked solid.I wish I had a rear brake that would work that well on my commando.
Anyway every single norton I own ,or have sold I have replaced that bearing if nothing else.A slidehammer behind the old one will remove it without taking the gearbox out or primary apart.I used a 1/4-20 standard threaded rod as a slidehammer and fitted a turned round piece on the other end which is slightly smaller than the inside diameter of the bearing .I left 1/16" thickness at the back to drop in behind the bearing.Make the round piece 1/2 to 3/4" long and thread it for 1/4 - 20. Then relieve most of the length ,leaving 1/16 at the one end.
Bruce
 
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I would not ride a Norton with the old layshaft bearing. When it locks so does the rear wheel. Not good. Even if you survive the skid, you and the bike will still need a lift home.
 

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geo46er said:
Hi Cal,
Yes, if your layshaft broke that would indeed be a very bad thing. Personally, I have never heard of one breaking, but, I'm sure that somewhere somehow someone has managed it.
GB

I visited my dealer one day back when my Norton was still in warrantee. Two of the mechanics were scaling clutch plates like Frisbees into the woods. "This is all that Barnett clutches are good for, unless you want to snap your layshaft".

Maybe there were some weak shafts made?
 
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I had a layshaft snap like a carrot one time! I think the needle bearing failed first.

Brewer.
 

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Hi BigBird,

I see you have another Commando ('75) and a Honda, so you don't need to rush the '74 into service. My opinion is any new Norton to your possession needs to be sorted for the usual weak points unless you know for certain from the previous owner it's already been done. When I bought my '72 combat in '97 the layshaft bearing was on my list and had not been replaced yet.

David
 
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my worst gear box disaster took out 6 gears, both shaft's, both shift fork's, 2 ball bearings and the main case. that was in 72 with a Barnett clutch and dropping the hammer at 7.000 RPM drag racing it.
 
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illf8ed said:
Hi BigBird,

I see you have another Commando ('75) and a Honda, so you don't need to rush the '74 into service.
David

The 74 belongs to my brother. The 75 is my first Norton and first Britt bike. I will be looking into someone to change out the lay shaft bearing.

Again, thanks for all the input
 
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I would suggest doing it yourself, with aid of one or both of Mick Hemmings's video on gearbox rebuilds and/or Fred Eaton's tutorials (free at oldbritts.com). I used both to rebuild a "spare" gearbox I bought off eBay. It was pretty easy - for a full rebuild including bushings, you will need to get pretty creative with heat, threaded-rod pullers, bushing removal via taps, and other unique skills, but not difficult at all (hey, if Mr. "Tighten til she strips, then back off 1/4" can do it, anyone can!). Good luck.
 
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