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#408856 - 12/16/11 12:55 am B31 gearbox oil level  
Joined: Nov 2011
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B31 Ally Offline
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Hello, i have a 1950 B31 plunger and i cant seem to find a gearbox oil level bung like on the later swing arm B31's. Mine has a round plug that you remove to adjust the clutch and i was wondering is this the oil level plug as well? The later gearboxes seem to have an oval plate held on with two nuts. Any ideas as to the oil level?

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#408880 - 12/16/11 4:40 am Re: B31 gearbox oil level [Re: B31 Ally]  
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pachy Offline
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Hi, i think your referring to the box thats the same as used on M21, i dont think they put a level plug on them, ive had several bikes with that box, its not alot of work to drain the box & just put the correct amount of fresh oil in, You can run that box packed with grease, or use same oil as engine & depending on which publication you read capacity is either 370cc or 570cc (1 pint) nothing is critical with those boxes but i do slap lots of grease all over the positive stop mechanism if i have the case off to change a kickstart spring.

#408927 - 12/16/11 2:57 pm Re: B31 gearbox oil level [Re: B31 Ally]  
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leon bee Offline
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On mine, I've just filled it about to the cover then it quickly leaks out to a comfortable level.

#408982 - 12/16/11 10:48 pm Re: B31 gearbox oil level [Re: B31 Ally]  
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B31 Ally Offline
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Northern Ireland
Thanks for the info guys, i do believe it is the same box as the M 21. My workshop manual is a haynes one but its for the later swing arm model but a lot of the info is the same for my bike. It talked about the oil level bung but my box didnt have it as its the earlier one. Yes Leon bee, they will leak themselves down to its own level all right! Thanks for the oil capacitys Pachy, i will give them a go and see how i get on.

#408997 - 12/17/11 12:39 am Re: B31 gearbox oil level [Re: B31 Ally]  
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Ignoramus Online content
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B31 Ally
Its called an "M series" gearbox ....they were initialy used on M and early B series but when B series bikes went to the newer box M series bikes continued with them till the end of production.

There is no oil level plug but like Leon says just fill it right up and let it find its own level. I use 80/90 gear oil and 20/50 mixed half and half in mine, I like the way the 20/50 foams up and will lubricate all the quite complex selector mechanism which is inside the outer cover.

almost invariably the sprocket oil seal on those boxes is stuffed (unless obiously theve been done) so keep an eye on your oil from time to time.


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
#409149 - 12/17/11 11:31 pm Re: B31 gearbox oil level [Re: B31 Ally]  
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Ignoramus Online content
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Ignoramus  Online Content
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or maybee replace the seal.


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
#409153 - 12/17/11 11:42 pm Re: B31 gearbox oil level [Re: Ignoramus]  
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shel Online content
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Originally Posted By: Ignoramus
or maybee replace the seal.


Heretic!


When given the choice between two evils I picked the one I haven't tried before
#409219 - 12/18/11 11:40 am Re: B31 gearbox oil level [Re: shel]  
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BSA_WM20 Online content
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Quote:
Its called an "M series" gearbox ....they were initialy used on M and early B series but when B series bikes went to the newer box M series bikes continued with them till the end of production.

Actually they are the Pre War heavy weight 4 speed box.
They use an oil slinger and a backwards spiral cut into the sprocket to hold the oil in.
These are very sensitive to the amount of clearance between the parts which after 70 + wears is liable to be on the larger end of the specifications.
The usual fix is to fit a modern sealed bearing.
Better still is to machine out the sprocket hole to take an oil seal and use the latter sprockets which are much easier to get than the ones with the spiral cut into them. There is sufficient space to machine a lip into the inside of the outer cover to hold back oil from the gearchange lever and by now it will need a new kick start bush which should be machined to match your kick start quadrant wit .0005" working clearance .


Bike Beesa
Trevor
#409293 - 12/18/11 8:05 pm Re: B31 gearbox oil level [Re: B31 Ally]  
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Ignoramus Online content
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Ignoramus  Online Content
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Auckland NZ
BSAWM20 recons:
"Actually they are the Pre War heavy weight 4 speed box.....
Better still is to machine out the sprocket hole to take an oil seal and use the latter sprockets which are much easier to get than the ones with the spiral cut into them"

That is not the gearbox that original poster, or myself was refering to, he is refering to " Mine has a round plug that you remove to adjust the clutch ".....you know the M series box with the oil seal fitted.


"There's the way it ought to be and there's the way it is" (Sgt Barnes)
#409916 - 12/23/11 12:13 am Re: B31 gearbox oil level [Re: ]  
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B31 Ally Offline
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Without wanting to cause a row, my gearbox has an oil seal on the out put shaft which was stuffed. Im now replaceing it so when i get it back into the bike, hopefully the oil will stay in where it was meant to....


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