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Gearbox Sprocket removal/replacement
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chickensoup
Bolton, Greater Manchester
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August 26, 2019 - 11:49 am
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20190825_105201.jpgWell today I thought I would have a look at changing over the gear box final drive sprocket (16 tooth), without removing fly wheel, and fly wheel inner case. I have thought about this before, and just wanted to see if it was possible to remove this sprocket, without all the hassle of flywheel and stator plate case removal.

I had the engine out of the frame because I was working on, and repairing the clutch. The manual says. “Removal of the engine from the frame should take no longer than 15 minutes”. Took me about an hour longer than the manual, but what the hell.

First item to remove was the clutch push rod, an easy removal. The first major problem I came up against was the lock washer, and how to bend back the tabs, In the end I used a pair of modified broken pliers, to squish back the tabs.

Remembering that the retaining nut is a left-hand thread, this was quite easily undone. Once the tab washer was removed, the sprocket was also quite easily removed from the shaft, after a bit of jiggling.

I would like to point out that I don’t feel you would be able to remove the sprocket from the shaft, if your sprocket size was anything larger than a 16 tooth type.

Re-instating the new sprocket was also quite easy, as was re-instating the washer and nut.

Not sure if this topic has been covered before. I just wanted to see if it could be achieved, whilst the engine was out of the frame, as the manual doesn’t tell you about replacing sprockets (engine in or out of the frame). I was quite pleased with the outcome, but feel it would probably be impossible with the engine in the frame.20190825_104916.jpg20190825_104426.jpg20190825_104435.jpg20190825_104930.jpg

1950 BSA D1 Plunger   242 UYW

1966 BSA D7  LBF 62 D

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BantamBaz
Reading Berkshire
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October 25, 2019 - 10:37 am
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Hello, just found this item, very interesting as I've noticed the sprocket on my D14 is loose. I guess this would apply to mine as well.

Didn't realise it was L/H thread. So good info.

Barrie.

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chickensoup
Bolton, Greater Manchester
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October 25, 2019 - 9:55 pm
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Hi Barrie,

I'm sure the D14 is a similar set up. I have found on my bantam and other bikes too, the sprocket always works loose a little, but cannot come off the shaft, nor can the nut unscrew because of the tab washer. It all seems to equate to a happy medium. It just requires a check now and then that the looseness isn't getting worse.

Nick

1950 BSA D1 Plunger   242 UYW

1966 BSA D7  LBF 62 D

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BantamBaz
Reading Berkshire
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October 25, 2019 - 10:53 pm
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Thanks Nick.

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AdrianS
Harlaston Staffs
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December 20, 2019 - 3:40 pm
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resurrecting an older thread ; re sprocket not being very tight. 

It is important that the nut is TIGHT before bending over the tab washer. I had one that was not very tight on my D7 in the 70s and the sprocket could "chatter" on the gearbox out put shaft. This resulted in wear to the sprocket centre and eventually the sprocket was spinning on the gear box shaft ( or final drive cog shaft) causing me to break down and a 7 mile push home! Thankfully the output shaft was virtually unmarked.

So....…………….. if your sprocket can move on the output shaft, you risk the same happening as I experienced.

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NeilB
Kidderminster
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December 20, 2019 - 4:14 pm
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I've tightened mine tight 3 times now, but each time I bend up the locking washer, the nut loosens slightly!

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chickensoup
Bolton, Greater Manchester
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December 20, 2019 - 10:27 pm
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Hi all,

Sorry I should of been more specific. Going back to my post in October, when I say loose, I mean a few thousands of an Inch ( Microns ) play. if the drive sprocket teeth are held between thumb and forefingers.

Hope this is now clearer.

1950 BSA D1 Plunger   242 UYW

1966 BSA D7  LBF 62 D

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mikef
Chatham Kent
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December 20, 2019 - 10:48 pm
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Neil, you have to make sure the nut is tight to start with then tap the lock washer on the edge of the nut so that it tightens it more. If tapping from the top, as you would be, then tap on the left hand side of the flat, hope that makes sense. Remembering that it's a left hand thread.
Mike.

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NeilB
Kidderminster
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December 21, 2019 - 1:13 pm
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That's what I did Mike, but as chicken soup says it's only a tiny amount of movement, I've had far worse on Japanese bikes purely because of the sprocket mounting design.

I was going to change the whole chain set at some point next year, so I'll get a new washer at the same time and see if it goes any better with the engine in the bike. 

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