I thought It was clutch slip, but I think it actually may be a gearbox, (1st gear) issue?

Britstuff

Britstuff

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Hi:

1974 MkII 850 Norton Commando. Been having an ongoing issue with "clutch slip" ever since I bought the bike and got her roadworthy. The clutch only "slips" in first gear, usually when I get to around 3000 rpm or so. No "slippage" noted in any other gear. To cut a long story short, I have learned way more about Norton Commando clutches than I ever thought I would need to know. Currently running a Norvil belt drive with 5 thin barnet fiber friction plates, 5 plain steel plates, a thin pressure plate and a pushrod (gearbox oil) seal. As stated above, in any gear other than first, no problem!

I recently noticed that when in first gear, if I hold the gear lever up with my right foot, the clutch does not "slip". It seems like the clutch is actually not the problem and the issue is that when in first gear and under load, the gearbox is trying to jump out of gear, although it is not making it to neutral. To put it another way, when in first gear, and I do NOT hold up the gear lever, and experience "slippage", when I release the throttle and the revs drop, first gear then re-engages, i.e it seems that the gearbox is not fully jumping out of first gear and into neutral - which of course, if it had, I would have pointed my finger at the gearbox as the source of the problem a long time ago!

Question: Anybody got any ideas about what could be wrong with the gearbox / what action I should take? The bike has approx 20,000 miles on it and the gearbox may not have been touched since new, although it is possible a previous owner may have made a mess of it. Regardless, I highly doubt it has ever been properly rebuilt. In regards to general operation, the gearbox works well, quite similar to my other two bikes, both of which are equipped with AMC type gearboxes.

Thanks!
 
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Britstuff said:
Hi:

1974 MkII 850 Norton Commando. Been having an ongoing issue with "clutch slip" ever since I bought the bike and got her roadworthy. The clutch only "slips" in first gear, usually when I get to around 3000 rpm or so. No "slippage" noted in any other gear. To cut a long story short, I have learned way more about Norton Commando clutches than I ever thought I would need to know. Currently running a Norvil belt drive with 5 thin barnet fiber friction plates, 5 plain steel plates, a thin pressure plate and a pushrod (gearbox oil) seal. As stated above, in any gear other than first, no problem!

I recently noticed that when in first gear, if I hold the gear lever up with my right foot, the clutch does not "slip". It seems like the clutch is actually not the problem and the issue is that when in first gear and under load, the gearbox is trying to jump out of gear, although it is not making it to neutral. To put it another way, when in first gear, and I do NOT hold up the gear lever, and experience "slippage", when I release the throttle and the revs drop, first gear then re-engages, i.e it seems that the gearbox is not fully jumping out of first gear and into neutral - which of course, if it had, I would have pointed my finger at the gearbox as the source of the problem a long time ago!

Question: Anybody got any ideas about what could be wrong with the gearbox / what action I should take? The bike has approx 20,000 miles on it and the gearbox may not have been touched since new, although it is possible a previous owner may have made a mess of it. Regardless, I highly doubt it has ever been properly rebuilt. In regards to general operation, the gearbox works well, quite similar to my other two bikes, both of which are equipped with AMC type gearboxes.

Thanks!
Click to expand...
Common symptom.

Ratchet pawl spring adjustment (Most likely)

Bent shift fork
Bent shift fork rod
Worn shift fork
Work engagement dogs
Gear selector assembled off by a tooth.
Worn/misassembled linkage limiting movement.


The false neutral "free wheel" you describe (and then comes back into gear) is the gear not going all the way in, and the shift quadrant bullet nose/spring not in position and not holding it in gear.
NOTHING like clutch slip, which usually is seen most predominantly in the higher gears.
 
Britstuff said:
Hi:

1974 MkII 850 Norton Commando. Been having an ongoing issue with "clutch slip" ever since I bought the bike and got her roadworthy. The clutch only "slips" in first gear, usually when I get to around 3000 rpm or so. No "slippage" noted in any other gear. To cut a long story short, I have learned way more about Norton Commando clutches than I ever thought I would need to know. Currently running a Norvil belt drive with 5 thin barnet fiber friction plates, 5 plain steel plates, a thin pressure plate and a pushrod (gearbox oil) seal. As stated above, in any gear other than first, no problem!

I recently noticed that when in first gear, if I hold the gear lever up with my right foot, the clutch does not "slip". It seems like the clutch is actually not the problem and the issue is that when in first gear and under load, the gearbox is trying to jump out of gear, although it is not making it to neutral. To put it another way, when in first gear, and I do NOT hold up the gear lever, and experience "slippage", when I release the throttle and the revs drop, first gear then re-engages, i.e it seems that the gearbox is not fully jumping out of first gear and into neutral - which of course, if it had, I would have pointed my finger at the gearbox as the source of the problem a long time ago!

Question: Anybody got any ideas about what could be wrong with the gearbox / what action I should take? The bike has approx 20,000 miles on it and the gearbox may not have been touched since new, although it is possible a previous owner may have made a mess of it. Regardless, I highly doubt it has ever been properly rebuilt. In regards to general operation, the gearbox works well, quite similar to my other two bikes, both of which are equipped with AMC type gearboxes.

Thanks!
Click to expand...
In addition to what @Fast Eddie said, if it is actually doing what you think, you likely have some badly worn parts and will probably soon have a very bad experience. IMHO, get on it soon rather than later while it's still savable.

Make sure the plunger (big "nut" near the bottom) is screwed all the way in. If it is, put the gearbox in any gear, be careful to not bump the gearshift, and remove the nut (oil will come out). Then inspect the plunger and spring it contains. It should move smoothly but be rather tough to push the plunger all the way down - that plunger is what keeps it in gear and holding the lever up is not letting it do its job 100%.
 
Thank you all for your very helpful comments. It sounds like a gearbox inspection / rebuild needs to be conducted in the near future......

Couple of questions:

1. Are there any warning signs of impending layshaft bearing failure? The main shaft on my gearbox does not appear to have any wear, in that there is no play and turns freely. Although of course this is when the gearbox is in neutral, so the layshaft is not coming in to play.

2. I will work on most things, but have never rebuilt a gearbox. I am thinking it may be wise to contract it out to a professional gearbox rebuilder. Any recommendations?
 
Britstuff said:
Are there any warning signs of impending layshaft bearing failure?
Click to expand...
As you pull away you can look down and the kickstart lever move, its the layshaft free at the drive side bearing allowing it to angle itself in the kickstart shaft bush and turn the whole kickstart.

That's if you catch it early, ignore or not see it and the next one is a locked rear wheel.
 
O.K. thanks, got it. Not something I want to experience.

Am I right in thinking that layshaft bearing failure is primarily a Commando problem, the gearbox reaching its limits with the increased power of the 750 and 825 CC engines? I hope it is less of a worry with my 650SS and 650 Model 31 AJS.
 
Britstuff said:
O.K. thanks, got it. Not something I want to experience.

Am I right in thinking that layshaft bearing failure is primarily a Commando problem, the gearbox reaching its limits with the increased power of the 750 and 825 CC engines? I hope it is less of a worry with my 650SS and 650 Model 31 AJS.
Click to expand...
It’s not due to power, it’s due to an inadequate bearing that was used at the time.

Remember, if the gearbox locks up you are pretty much in the hands of fate… you can’t even pull the clutch in to save yourself.

With the layshaft issue AND the rather ominous sounding issues that you have, I would suggest you don’t ride that bike until the gearbox is sorted.
 
If you don't want to tackle the MK 111 gearbox rebuild , then perhaps ship it to Greg Marsh , seeing as you are both somewhat in Central East U.S. He will make it better than new for you .
I have 2 MK 111's and recently tackled both of the boxes at the same time. Both were having issues with first gear and particularly neutral .
Inspection showed deep slots worn into a peened in little ball protrusion on the cam plate inner side , used in conjunction with activating the neutral light switch . Andover Norton now sells an improved button and improved switch . I'm convinced this was a contributing issue .
Both boxes also received roller layshaft bearing( s ) , 1 St. gear bush , springs , seals etc.
Both layshafts were also shimmed as per an Old Britts article , to help prevent popping out of first gear .
Shifting is like butter now with no first or neutral issues .
Good luck either way you choose .
 
There are lots of guides, hows and videos on doing full gb rebuilds. I got the Mick Hemming gb rebuild dvd from the inoc and it is everything you need to know. Im no mechanic and never done any gb prior. Worked out well for me.
The layshaft bearing was the failure prone portuguese type, at 10k miles but not yet failed, replaced it with hemmings recomended phenolic cage deep ball bearing type. I did the whole
Job with gb still in frame...but would be somewhat easier off bike. All bushes, bearing, springs and seals renewed.
 
Thank you everyone for your help and advice. I do not fancy the idea of a locked up rear wheel, so I am going to take the old girl off the road and send the gearbox to Greg Marsh for repair.

From what I can see, removing the gearbox from the cradle is achieved by firstly removing all surrounding bits and pieces and rotating the gearbox anticlockwise by approx 90 degrees to allow it be withdrawn from the timing side.

While I am in there I will probably install some rear suspension trailing arm clamps.

Funny how these projects tend to experience "mission creep". When I bought the bike, I thought she would be a quick and easy fix. Oh you poor, sweet, innocent child..... When she goes back on the road next year, the only thing on the bike that I will not have rebuilt or replaced is the motor bottom end!
 
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Britstuff said:
Thank you everyone for your help and advice. I do not fancy the idea of a locked up rear wheel, so I am going to take the old girl off the road and send the gearbox to Greg Marsh for repair.

From what I can see, removing the gearbox from the cradle is achieved by firstly removing all surrounding bits and pieces and rotating the gearbox anticlockwise by approx 90 degrees to allow it be withdrawn from the timing side.

While I am in there I will probably install some rear suspension trailing arm clamps!

Funny how these projects tend to experience "mission creep". When I bought the bike, I thought she would be a quick and easy fix. Oh you poor, sweet, innocent child..... When she goes back on the road next year the only thing on the bike that I have not rebuilt is the motor bottom end!
Click to expand...
Just sent a PM telling you how to get it out.
 
The reason many of us like old motorcycles is they are rebuildable. The first time we pull any motorcycle apart without experience can be a worry. However fixing it is usually straight forward and logical. And we learn by doing it. The only worry with a Norton gearbox is remembering how to time the cam plate. I ran into a silly problem with the 6 speed TTI box. I did not remember how to re-attach the clutch cable to the lever arm inside the box and fiddled around with my fingers, then walked away in disgust. Then thought about it and bought a pair of needle-nose pliers. Then I found the pair which should have been in my shed. That cable is probably the only reason I have ever had needle-nose pliers. I think my bike might be going again next week-end. When I was younger, I never had to think when preparing my motorcycle. It was automatic.
A gearbox explosion is an almost certain crash of the worst kind.
 
Thinking about fixing things can be worse than putting your brain into neutral and actually doing it. A motorcycle engine or gearbox usually only goes together in one way, and any wear is usually easy to detect. The only thing which can only cause real trouble is fitting the circlips in pistons, which hold the gudgeon pins in place. If they are not in right - big bang.
 
Britstuff said:
Thank you everyone for your help and advice. I do not fancy the idea of a locked up rear wheel, so I am going to take the old girl off the road and send the gearbox to Greg Marsh for repair.

From what I can see, removing the gearbox from the cradle is achieved by firstly removing all surrounding bits and pieces and rotating the gearbox anticlockwise by approx 90 degrees to allow it be withdrawn from the timing side.

While I am in there I will probably install some rear suspension trailing arm clamps.

Funny how these projects tend to experience "mission creep". When I bought the bike, I thought she would be a quick and easy fix. Oh you poor, sweet, innocent child..... When she goes back on the road next year, the only thing on the bike that I will not have rebuilt or replaced is the motor bottom end!
Click to expand...
The transmission can be first inspected, and repaired in the frame, so much faster & easier.
8DBB2F96-56AF-4B27-A6E8-DF12C2C1424B.jpeg
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4D3CA4F7-9468-4E1E-9D28-F0B1669F726D.jpeg
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I ended up removing the gearbox form the bike (thank you @marshg246 for the tips on how to do so) and decided to disassemble and inspect the gearbox myself. First off, it does have the original "Portugal" layshaft bearing. So clearly this was an exercise worth doing. Secondly, I wanted to confirm that first gear was slipping / was not properly engaging. I think the evidence of first gear slipping is pretty compelling, please see picture below of the layshaft first and second gears:

Of course the question now is why is first gear slipping? I think I know why, and I am hoping someone can confirm or debunk my theory. I noted when I stripped the gearbox that the kick start shaft seemed to have a lot of end float. I foolishly did not measure it, but it was obviously way above spec. One thing I am not sure about is were layshafts shimmed from the factory? Or is shimming the layshaft something that is only done to compensate for the width of the replacement for the "Portugal" layshaft bearing? I think it is highly likely that the inner cover on my gearbox has not been opened since it left the factory and there were no shims present.

I did notice that the Index plunger appears to be be working correctly. There was also some other general wear, but nothing that stood out to me as being particularly bad. That, said once I get a better idea of what is going on with the first gear slippage, I will do a closer inspection of the remaining parts.

Thank you!
 

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Britstuff said:
I ended up removing the gearbox form the bike (thank you @marshg246 for the tips on how to do so) and decided to disassemble and inspect the gearbox myself. First off, it does have the original "Portugal" layshaft bearing. So clearly this was an exercise worth doing. Secondly, I wanted to confirm that first gear was slipping / was not properly engaging. I think the evidence of first gear slipping is pretty compelling, please see picture below of the layshaft first and second gears:

Of course the question now is why is first gear slipping? I think I know why, and I am hoping someone can confirm or debunk my theory. I noted when I stripped the gearbox that the kick start shaft seemed to have a lot of end float. I foolishly did not measure it, but it was obviously way above spec. One thing I am not sure about is were layshafts shimmed from the factory? Or is shimming the layshaft something that is only done to compensate for the width of the replacement for the "Portugal" layshaft bearing? I think it is highly likely that the inner cover on my gearbox has not been opened since it left the factory and there were no shims present.

I did notice that the Index plunger appears to be be working correctly. There was also some other general wear, but nothing that stood out to me as being particularly bad. That, said once I get a better idea of what is going on with the first gear slippage, I will do a closer inspection of the remaining parts.

Thank you!
Click to expand...
Shimming, in theory, is not needed when you have the ball bearing for the layshaft as the layshaft does not float. So, how hard was it to get the layshaft out? If it just slipped out then either the bearing was not tight in the shell or the bearing was not tight on the layshaft.

The marks you see may mean first gear slipping or may just mean the layshaft was floating and there was some interference between the gears when running. Those dogs go well into those holes - to be in first gear and not actually engaged, to me, means look more. Put it all together laying on the bench and visualize it all. That may make it more clear.
 
Shimming for end float not done from factory AFAIK...and only done when using a roller bearing in place of a ball bearing for layshaft. One of the advantages of using the deep groove, phenolic cage ball bearing instead of a roller set....no shimming. Hemmings states in his gb rebuild video a roller bearing can lead to layshaft breakage b/c it is held to rigidly by roller type compared to ball type.
 
Britstuff said:
One thing I am not sure about is were layshafts shimmed from the factory?
Click to expand...
No, the layshaft should be a tight enough fit in the ball bearing so it cannot move in normal use. So if you have endfloat in a ball bearing fitted gearbox either the ball bearing is badly worn, the ball bearing is loose in its housing or the shaft has been worn undersize.
 
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