Smiths speedo gearbox repair

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DogT

DogT

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Just to follow up on some previous threads about this item. I took a small chisel, inserted it in the small hole in the gearbox after removing the tophat spacer and with a small hammer punched the ring out of the other side of the gearbox. It was easy, it could be done with a flat bladed screwdriver. Next pull out the felt washer, the metal ring and then the ring gear with the dogs. I think this is about all you can get apart.

If you look closely at the closeup of the housing, you can see that my gearbox is worn where it has been in contact with the bearing spacer, and may have been the reason my hub cover was chewed up a bit as well as the cover ring on the gearbox, you can see the numbers are about worn off. I think like someone else said, that the housing is also pushed out where the tophat spacer is, and both these issues are probably a result of assembling the rear wheel without getting the dogs fully engaged before tightening the spindle. I think I am going to try to solder or otherwise install a washer where it has been rubbed and thined after cleaning and re-bend the outer part enough so the gearbox does not contact the hub cover.

Any better ideas?

Smiths speedo gearbox repair


Smiths speedo gearbox repair


Dave
69S
 
Just an added item re disassembly - you can punch out/cut the 4 rivets and remove the retainer plate and the ring gear if you wish to. For reassmbly, it is not necessary for the retainer to be there - it just keeps the gear from falling out of the unit when it is not installed on the bike. The gear is held in position by the dogs in the rear hub and the retainer has no beneficial effect on operation. If you remove the rivets, you need to seal up the holes to keep the grease in and dirt out. I just used small self-tapping screws. Is there any real point in removing the retainer? Not really as far as I can see! :)
 
MexicoMike said:
you can punch out/cut the 4 rivets and remove the retainer plate and the ring gear if you wish to. For reassmbly, it is not necessary for the retainer to be there - it just keeps the gear from falling out of the unit when it is not installed on the bike.
Click to expand...

Actually, it doesn't.

As I'm sure it can be seen from the photo below, the ring gear can't fall out-unless the outer ring (and felt washer) has been removed.

Smiths speedo gearbox repair


Personally, I wouldn't want to use a drive gearbox without the retainer, as I believe it's there to keep the ring gear centralised within the unit?.
 
LAB,

I see that ring that is on your retainer. Mine doesn't have it, and it looks like it was never there, not ground away, because there are tool marks on my retainer that go almost all the way across the retainer. Perhaps it was a later invention? My ring gear just sort of floats around in the case. In my case all my retainer seems to do is take up space or reinforce the housing? I guess if the dogs engage the lock ring on the wheel it is not going anywhere as long as it is centralized so it won't chew up the housing.

Dave
69S
 
DogT said:
I see that ring that is on your retainer. Mine doesn't have it, and it looks like it was never there, not ground away, because there are tool marks on my retainer that go almost all the way across the retainer. Perhaps it was a later invention?
Click to expand...

The retainers always had the lip-as far as I know?
Smiths speedo gearbox repair


Smiths speedo gearbox repair


Smiths speedo gearbox repair
 
You are right that the felt will keep the gear from falling out if the felt is there. Mine didn't have any felt. I removed the retainer because you couldn't turn the ring gear by hand when it was removed from the bike due to the interference fit of the retainer. I didn't like that and I can't see how it has any effect on centering because the force involved with the hub/dogs/ring gear is many orders of magnitude beyond anything that retainer can resist. So the gear is going to end up "centered" to wherever the hub/dogs/gear want it to be, retainer or not. Frankly, I think the whole assemble is a better "fit" and works more smoothly without the retainer. But you guys have a lot more experience with all this than I do.

And Yeah LAB, where DO you find this stuff?
 
Mine must be the exception. The Patent number on the outside is 529397. Otherwise appears pretty much as your photo. Here you can see the 4 circular machine marks that would not be there if there was a raised rim on the retainer that was rubbed off. Who knows???

Smiths speedo gearbox repair


Dave
69S
 
MexicoMike said:
You are right that the felt will keep the gear from falling out if the felt is there.
Click to expand...

It's the large steel retaining ring that stops the gear from falling out, presumably yours was there, even if the felt was not? :roll: As the gear is too big to pass through hole in the ring.





MexicoMike said:
And Yeah LAB, where DO you find this stuff?
Click to expand...

It's just a matter of looking in the right places I suppose?
 
I can't ever remember seeing that type of flat retainer before?


DogT said:
The Patent number on the outside is 529397.
Click to expand...

They all (Smiths, not pattern) seem to have the "529397" number regardless of the box model type. Is the drive box model number stamped into the steel ring still legible?
 
The BG5330/171 is visible, but mostly by looking at your number, I would have a hard time coming up with the numbers on my own, but am pretty sure. The Word RATIO is clear and deep, but the number is gone. There is also a number inside you can see in my photo, 31-134-267-00.

Dave
69S
 
DogT said:
The BG5330/171 is visible

The Word RATIO is clear and deep, but the number is gone.
Click to expand...

BG5330/171is the correct number for a pre-MkIII Commando (unless of course the ring originally belonged to a different unit?) and the ratio should also be 15/12 (1.25:1).
 
I'm fairly sure it is the original unit off the 69 "S". I bought it in 72 and did not change anything other than the exhaust.

Dave
69S
 
I did wonder if that flat retainer could be a repair job? Still, let's see if any of our other members have seen retainers like that?
 
LAB,

Does that diagram you have show the clearance between the ring gear and the housing and the large round washer that is under the felt. It appears that the felt is just to keep the grease in and dirt out since it sits between the large round washer and the cover?

Dave
69s
 
DogT said:
Does that diagram you have show the clearance between the ring gear and the housing and the large round washer that is under the felt.
Click to expand...

It doesn't, but the unit in my photo (which is a pattern item, incidentally) has a gap of approximately 0.040" between the ring gear and the inner steel washer.
I can probably find another low mileage genuine Smiths unit (tomorrow) to check the clearance between the ring gear and the housing, and confirm the ring gear to washer measurement, unless anyone else cares to give you that information in the meantime?
 
Getting it apart and knowing whats inside is good, but when these things fail are any of the internal parts available from the usual list of British part suppliers??
GB
 
GB,

Apparently not. I think many have searched and not found, like me.

Dave
69S
 
L.A.B. said:
DogT said:
Does that diagram you have show the clearance between the ring gear and the housing and the large round washer that is under the felt.
Click to expand...

It doesn't, but the unit in my photo (which is a pattern item, incidentally) has a gap of approximately 0.040" between the ring gear and the inner steel washer.
I can probably find another low mileage genuine Smiths unit (tomorrow) to check the clearance between the ring gear and the housing, and confirm the ring gear to washer measurement, unless anyone else cares to give you that information in the meantime?
Click to expand...

I've measured another unit, (original Smiths this time)

"Ring gear to washer" - about the same = around 0.040"
"Clearance between the ring gear and the housing" = 0.034"
 
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