BSA B25s Beginner

[Jim_Hines]

Hi,
I've just bought my first BSA. It's a 1970 B25s and I love it.

I've never owned an old bike before, having only ever had and ridden modern Husqvarna Enduro and Supermotos that required very basic maintenance from me.

So I'm very new to old British engineering but I'm keen to learn as much as I can with my first classic.

Can anyone help me with my first issue that I've come across please?

I've noticed oil weeping out of the front of the primary chain case, through a "gromit" which has a pair of sheaved cables going into it. I'm wondering if it's just been overfilled and that's the excess weeping out?

I've attached a photo to help explain...

Thanks,
Jim

[SJCLARKE]

Hi Jim it could be as you say overfilled or it could be the breather that is blocked this is the pipe on the crankcase where the clutch cable goes through next to breather regards, Steve

[Jim_Hines]

Hi Steve,
Thanks for your reply.
I'll check the breather tonight and go from there.

Thanks for your help.

[Jim_Hines]

Hi Steve,
To check the breather pipe is clear, how would you do it? I was going to feed a thin piece of wire down it? but wanted to check first...

Thanks.

Jim

[Beesy]

You could try that, but I think it will be fiddly and perhaps inconclusive as the wire will need to bend 90 degrees to make it through.

I think I'd prefer to remove it to check it, again getting it off and back on will be a bit of a pain, I expect the chain and guard will have to come off to make it easier.

Have you checked the oil level, that's a lot easier.

[Jim_Hines]

Ok, understood...

Do you mean check the oil tank under the seat?

If so, I've already checked that and it's fine.

[neil1964]

Ok, understood...

Do you mean check the oil tank under the seat?

If so, I've already checked that and it's fine.

No, I am pretty sure he means the primary chain-case.  I believe this has its own oil I believe approx 225mls.
Some later unit singles do not have an oil seal between the crankshaft and the chain-case and the engine 'breathes oily fumes into the chain case.  There is then a hole in the crankcase that allows the excess oil that accompanies the air to drain back into the crankcase and get scavenged away by the oil pipe pick up in the bottom of the crank. I know B50s have this but not sure about a  1970 B25 someone more knowledgeable should be able to chip in?

[Beesy]

Sorry meant check the primary chain case oil level.

See attached pic. Put bike on centre stand on level ground.

Undo screw M. It has a drain hole in that is used to measure the chain case oil.

If it has been over filled, oil will come out, when it stops, you have the correct amount.

Alternatively, you can drain all the oil from Nut N and refill with a 1/4 pint. I use 10/30 oil.

It'll also be worth checking the grommet is still OK. The chain in the case runs anti clockwise, so it'll fling oil directly on the back of that grommet.

Replacing it is pretty simple, there should be some bullet connectors to gently disconnect, remove the old grommet gently with maybe some long nose pliers and old blunt screw driver or similar taking care to keep in one piece. Cover the new one in oil to make it slippery and gingerly tease it into the hole with something blunt so not to damage the grommet.

[Jim_Hines]

Morning Beesy,

Sorry for the late reply!

Thanks for your messages.

Ok that all now makes sense.

Oil level is good. So narrowed it down to the grommet.

Have you any idea where I can source a gromit to fit in there? Seems a simple enough job.

Thanks again for all your help.

[Beesy]

Here's a couple of places, Feked and Ebay.

https://www.feked.com/bsa-alternator-or-contact-breaker-leads-wiring-grommet-a50-a65-b25-b50-bantam-models.html

Check out BSA C15 B25 C25 B44 B50 TR25 A50 A65 ALTERNATOR LEAD GROMMET 40-0705 on eBay!
https://www.ebay.co.uk/itm/115380877472?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=9mwnzYwPSJi&sssrc=4429486&ssuid=mr0-6ZYKTLm&var=&widget_ver=artemis&media=EMAIL


Im not saying it isn't a blocked breather, but it might be a knackered grommet (or even both together).

If it isn't the grommet, check the breather tube, I would remove it so that I could ensure its thoroughly cleaned. It'll be a bit of a faff as it would be best to remove the chainguard and chain to do it.

You could try poking something up it, but personally I don't think it would work very well.

[rogerfastlane]

Yes, they go hard after all those years so don't seal. Simple to replace but you have to remove the alternator
cable to do this so may need a new chaincase gasket (if fitted and not using gasket goo).

[Jim_Hines]

Morning all,
Thank you for all your help.

Ordered the gromit from eBay, which arrived very quickly.

Was a bit tricky to get the old grommet out, and had to take the chain case off to get to the inside and push it forward.

But all done now and and appears to have done the job.

Thanks for everyone advice.

Onto the next issue now...

👍