Author Topic: B31/B33 primary chain oil  (Read 376 times)

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Greenfield

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B31/B33 primary chain oil
« on: 21 March, 2022, 10:59:16 »
Looking at the instruction manual for my B33 plunger it says that the B31 and B33 swinging arm models, plus B32 and B34 all have 225cc of oil in the primary chain case. However the B31 and B33 plunger models should only have 55cc. This tiny amount would lie in the bottom of the case and I doubt whether it would reach the primary chain to provide any lubrication. However, if oil is added up to the level plug, considerably more than 55cc, the chain etc would receive lubrication without the clutch plates sitting in oil. Can anyone advise the best amount of oil to use?

Spaceman

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Re: B31/B33 primary chain oil
« Reply #1 on: 21 March, 2022, 12:56:26 »
I'm no pre-unit single expert but I believe the SA models had a different design of chaincase, in which case, it's probably hard to read across from the plunger models. In general, the oil is there to provide the minimum of lubrication of the primary chain and, clearly, the oil level must be such that the chain is wetted reasonably regularly but it doesn't have to run in an oil bath. That said, I wouldn't have thought there was much of a downside in increasing the amount of oil in the chaincase within reason other than, maybe, more oil leaking out of the back of it?

LightningAndStarfire

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Re: B31/B33 primary chain oil
« Reply #2 on: 21 March, 2022, 13:02:06 »
Excess oil will cause a loss of power when the clutch basket drags in oil. The oil will also heat up imho.

DAVE BRADY

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Re: B31/B33 primary chain oil
« Reply #3 on: 21 March, 2022, 14:20:09 »
Hi,

Try the 55cc and check to see if the chain gets oily.  If not then pour a bit more in until the chain gets oily but record how much for future reference.

Dave.

martinh10

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Re: B31/B33 primary chain oil
« Reply #4 on: 21 March, 2022, 15:17:43 »
BSA Service Sheet 312 for S/Arm B31/33 gives 1/7 pint (80cc) for magneto models and 1/2 pint for alternator. Service Sheet 701 for plunger doesn't give a chaincase capacity but I have always filled to level plug which is 120cc - what else could a level plug be for?

Barrieh

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Re: B31/B33 primary chain oil
« Reply #5 on: 21 March, 2022, 16:18:41 »
I found that putting too much oil impacted the clutch plates causing them to drag.

I would suggest a smallish amount in. It gets wiped around in there and so not a lot is needed.

B Murphy

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Re: B31/B33 primary chain oil
« Reply #6 on: 22 March, 2022, 11:15:29 »
A snip from Classic Bike Hub

"The B31 clutch has a case of its own within the primary chaincase to allow it to run dry. The chaincase contains a small amount of oil, but this is to lubricate the primary chain rather than the clutch itself".

Greenfield

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Re: B31/B33 primary chain oil
« Reply #7 on: 22 March, 2022, 17:35:01 »
55cc is not enough to touch the primary chain but roughly double that amount brings it up to the level plug and allows the chain to be lubricated. So, as Martin says, 120cc looks about right, and why fit a level plug if not for a reason. I've added a pic showing how the level plug is positioned so low down on the case, the clutch will only be lubricated by splashes from the chain.
Cheers everybody