Final Drive Sprocket -end play on shaft -allsorted out!

I have the outer and inner primary chaincases off of my Mark 3 to deal with a leak with new gaskets, and to tighten things up in general.

I just noticed that my final drive sprocket (aka 06-0931, Gearbox Sprocket, 20 tooth) has what appears to be excessive back and forth play along the mainshaft.

The mainshaft itself has no end play, but the sprocket moves along the mainshaft by about 1/10" of an inch (2.5 mm for the non- US members).

maybe this is how it is supposed to be but it seems like a lot of movement to me?

Note: it moves toward the gearbox until it hits something (presumably the circlip on the gearbox side of the sprocket, 06-4989) but does not come in the other direction all the way to the other circlip (on the primary side of the sprocket).

1. Is this amount of play normal?

2. If not, what is the likely culprit?

3. Any problem leaving it this way even if it is too much play?

Sage advice, as always, greatly appreciated.

NOTE: the sprocket is tight, at 80 fp I assume (I didn't remove it). The sprocket and whatever it is attached to (4th gear main?) are moving together on the shaft.

Photo below:




Here it is pushed all the way "in" (toward the gearbox)




And here it is pulled out toward the primary side, with somewhere between 1/10" to 1/8th" ( 2 to 3 mm) of play:

Re: Final Drive Sprocket - end play ?

I've never been into a Mk3 primary, so don't know about 'sage' advice, but aren't they like all earlier Norton boxes there,
that have a large nut to hold the sprocket tight on the output sleeve gear - and a multistarred locking washer to hold that nut solidly there.

Being loose could allow it to float around, and the chain to wear into something, probably the primary case.

Re: Final Drive Sprocket - end play ?

Rohan said:

I've never been into a Mk3 primary, so don't know about 'sage' advice, but aren't they like all earlier Norton boxes there,
that have a large nut to hold the sprocket tight on the output sleeve gear - and a multistarred locking washer to hold that nut solidly there.

Being loose could allow it to float around, and the chain to wear into something, probably the primary case.

Click to expand...

The locking washer is in place, and I don't think I ever removed it in the 7 years (and 14,000 miles) that I have owned the bike. Guess I will remove the washer and see if I can tighten down the nut to remove the free play.

Re: Final Drive Sprocket - end play ?

Is the sprocket spacer (04-0131) in place behind the oil seal? It is about that size



(37) https://www.oldbritts.com/1975_g6.html

Re: Final Drive Sprocket - end play ?

040131 can not be the problem, it has nothing to do with the mainshaft, it is sandwiched between the big bearing and sprocket, its main purpose is for the seal to run on .
The mainshaft should have no end play as it is fixed at the other end by its nut against the right side bearing. I would guess the nut is not tight or the bearing (right side) is floating backwards in the inner cover.

Re: Final Drive Sprocket - end play ?

You might have a sleeve gear bearing outer ring sitting loose in the gearbox shell.

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

It would be wise to disassemble the transmission for inspection.

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

Sleeve gear bushings? And maybe worn mainshaft under the sleeve bushings? And, as mentioned, sleeve gear bearing.

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

pete.v said:

Sleeve gear bushings? And maybe worn mainshaft under the sleeve bushings? And, as mentioned, sleeve gear bearing.

Click to expand...

+1 the main shaft is held in position by the bearing and nut at the inner cover end. So it would seem the sleeve gear bearing is no being held by the gearbox shell.

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

I don't know how long this free play has been there.

So, bottom line ..... should I just put the primary back together and ride, or do I have to solve this problem? ( I have never messed with a transmission before and prefer not to if I don't have to)

The current situation means:

1) the sprocket can slide in and out on the shaft, thus possibly causing very minor additional chain to sprocket wear from slight misalignment as I am riding (not sure if there is enough play to actually cause this?)

2) 4th gear main and 4th gear lay can get slightly mis-aligned, but if would only be for a very small fraction of their engagement area, so I can't imagine this is an issue.

Do I need to fix this or can I put it back together and ride?

Thanks

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

My experience has been that when put together properly Commandos are quite reliable. However something like this will likely fail and should be corrected.

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

pkeithkelly said:

....I don't know how long this free play has been there. .......Do I need to fix this or can I put it back together and ride? Thanks

Click to expand...

Well you could JUST put it back together and JUST hope for the best, but wondering when it might fail would spoil it for me. maybe it would be when you found yourself in traffic and needing to pass a truck or car etc... maybe coming out of a lefthand downhill sweeper leading into a switchback, I mean who knows...it would always be in the back of my mind. I'm just sayin' :roll:

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

Keith, I suspect like others have said it almost has to be either the bearing outer not being held by the gearbox casing or the bearing inner coming adrift. Loose or disintegrated mainshaft bushes will not give this symptom. You must resolve this problem before riding the bike again, a seized gearbox can kill you.

I note that the sprocket nut seems like it is fitted the wrong way round, the chamfers are to allow the nut to fit correctly into the slight concavity of the sprocket outer face. Having said that I have just looked at an assembled gearbox that I happen to have on my bench and the number of threads exposed in your photos would seem to preclude a loose sprocket nut.

Don't be intimidated by having a look inside the box, you can do most, if not all, that you need to do without removing the gearbox casing from the bike. There is also lots of information and assistance available in manuals and on this site.

Good luck

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

As the primary and clutch are already off then as other have said just ignoring this will cost you more in the future. More damage to the gearbox and maybe the rest of bike if you have an accident. More importantly damage to yourself if the worst happens.

The gearbox internals can be removed with the casing still in the bike (in rear cradle) even the suspect bearing removed by heating case while its in the bike. The only reason to remove gearbox case is if it is cracked between main an layshaft bearing thus allowing bearing to break free (a common problem )

This site is full of knowledge tips and people only to happy to help you if you have a problem (as we are doing now) and it is not as hard as it looks. Just take your time and lots of pictures as it comes apart that will help show you how to reassemble it.

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

Folks - I appreciate the advice and suggestions but still do not know what the issue is, and thus what to tackle.

Part of the problem is that some folks are using parts descriptions that don't match the descriptions I am looking at in the parts schematics (Group 6, OldBritts). I'm not questioning the common descriptions, but I don't necessarily follow the conversation if I don't know what is being referenced.

First, to clarify the problem I am investigating: The Mainshaft has NO end play. It is not moving.

The Gearbox Sprocket (06-0931) is securely attached to the 4th Main, Sleeve Gear (06-5954). It is this assembly that is moving in and out on the Mainshaft.

pete.v said:

Sleeve gear bushings? And maybe worn mainshaft under the sleeve bushings? And, as mentioned, sleeve gear bearing.

Click to expand...

Pete - what is the "sleeve gear bearing?" I see Part No. 04-0098 which is described as the Left Hand Mainshaft Ball Bearing. Is this what you mean?

dave M said:

Keith, I suspect like others have said it almost has to be either the bearing outer not being held by the gearbox casing or the bearing inner coming adrift. Loose or disintegrated mainshaft bushes will not give this symptom.

Click to expand...

Dave - when you refer to the "bearing outer" and the "bearing inner" are you talking about the Mainshaft Bearing (04-0098)?

slimslowslider said:

You might have a sleeve gear bearing outer ring sitting loose in the gearbox shell.

Click to expand...

I ordered a trailer hitch wrench on Amazon for $11 to take off the Gearbox Sprocket nut as a starting point.

slimslowslider said:

You might have a sleeve gear bearing outer ring sitting loose in the gearbox shell.

Click to expand...

Again, looking for clarification - the "sleeve gear bearing outer ring?"

Again, thanks so much for the pointers.... looking forward to resolving this so i can ride.

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

Keith, I obviously misread your first post, I thought it was your mainshaft float, now I realize its the sleeve gear/sprocket assembly problem
If the sprocket nut is tight and it appears to be then the problem can only be the sleeve gear bearing is floating in the housing. it should be an interference fit , but its very common for the bearing to lose its interference fit over time for different reasons.
it wont get any better. a complete strip down will reveal all, you will probably find the bearing loose in the housing.

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

Madass -

Thanks for the quick response.

Yes, I guess I will have to open the patient up to see why the sleeve/gear/sprocket assembly is floating along the length of the Mainshaft.

But again, what is the "sleeve gear bearing?" Others have made reference to it as well, but I see no such part on the parts diagram.

I assume you mean the "Left Hand Mainshaft Ball Bearing" (04-0098).

Is that what you are referring to?

If so, it looks like its outer face fits into a recess on the right hand side of the Gearbox Shell, while the inner face is around the "4th Main Sleeve Gear"

Thanks again, much appreciated.

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

pkeithkelly said:

I assume you mean the "Left Hand Mainshaft Ball Bearing" (04-0098).

Is that what you are referring to?

If so, it looks like its outer face fits into a recess on the right hand side of the Gearbox Shell, while the inner face is around the "4th Main Sleeve Gear"

Thanks again, much appreciated.

Click to expand...

Yes, that is the correct bearing. The diagram misleads and is simply showing the direction of insertion, from the right. It will reside on the left side of the case being inserted from the right, pretty much before anything else, i believe.

The sleeve bushings and the integrity of the mainshaft underneath may contribute to this play and most certainly effects clutch wobble. When I did my sleeve and new mainshaft, that was the time to add the Maney outrigger. I do not know if you have that option or inclination, have a MKIII.

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

as Pete said that is the bearing, it sits behind the sprocket just inside the gearbox shell, all will be revealed when you dismantle.
after disassembly you will see there is not much metal between the sleevegear bearing pocket and the layshaft bearing pocket, its only about 1mm.
there is often a crack at this point which allows the 2 bearing pockets to open up in diameter thus diminishing the bearing interference fit, therefore allowing the outer race of sleevegear bearing to spin in the housing therefore wearing the housing and allowing the bearing to move backwards and forwards. dismantle and you will see.

Re: Final Drive Sprocket -end play on shaft -what's wrong? H

Working from the outside of the gearbox (these parts need to come off to strip the box anyway) remove the drive chain sprocket from the sleeve gear.
You should then be able to see the oil seal and spacer that the seal runs on. Using small screwdrivers or other sharp pointed tools even drilling tiny holes an screwing in small self tapping screw then pull on screw you should be able to prize out the seal without to much force. This will wreck it but they are cheap to replace an should be changed anyway as should the spacer if it shows even the slightest sign of a groove made by the seal.
Now you should be able to see the inner race of the bearing ( yes the one you Pete V and Madass are talking about ) and by pulling and pushing the sleeve gear see if...
1. The sleeve gear moves but the bearing stays still.
2. The bearing an sleeve gear move together. (The most common i believe)

To fix either will still mean stripping the box and as i said before you can strip box in the bike ( if i remember it does explain how to in the manual). At least this way you should have a better idea of what is wrong before going any further.
Gearbox rebuilds are not beyond most people but the costs of parts can very quickly add up. They are somewhat over stressed items though an you should not realy skimp or buy cheap parts or you may be back inside there alot quicker than you think.
On the plus side your skills an confidence will take a big boost when its all sorted (which is always nice).