B31 - Do I need to add oil?

[Fraz]

When I removed the right hand side case to replace my clutch push rod, oil came out.

When I'm putting it all back together, do I need to add oil or will it get oil from the sump?

If I do need to add some, how much please?

Many thanks

[neil1964]

That cover is the end of the gearbox only - no communication with engine on a plunger B31.
The oil will be gearbox oil so you will need to have the bike on level ground, use a small funnel aimed through the knurled circular that you have removed from the end cover.

Remove the level plug (note - NOT the drain plug - see handbook) and top up with whatever gearbox oil you are using (some people swear by a straight engine oil SAE 40 in Summer - I guess, personally I use EP90

Once oil comes out of the level plug you can stop and then put level plug and filler cap back.
I would not be tempted to over-fill as it will try to exit via the kickstart and gear lever shafts, or, if unlucky the oil seal behind the gearbox sprocket!!

[Fraz]

That cover is the end of the gearbox only - no communication with engine on a plunger B31.
The oil will be gearbox oil so you will need to have the bike on level ground, use a small funnel aimed through the knurled circular that you have removed from the end cover.

Remove the level plug (note - NOT the drain plug - see handbook) and top up with whatever gearbox oil you are using (some people swear by a straight engine oil SAE 40 in Summer - I guess, personally I use EP90

Once oil comes out of the level plug you can stop and then put level plug and filler cap back.
I would not be tempted to over-fill as it will try to exit via the kickstart and gear lever shafts, or, if unlucky the oil seal behind the gearbox sprocket!!

Thank you for your detailed response.

Only a little oil came out so maybe it was running low?

There does seem to be "clean" oil seeping to this area via a small hole almost below the kick start shaft, at the lowest edge - which I've plugged with a paper towel whilst I've got the casing off, hence me wondering if the area was fed from elsewhere.
Thanks again, I'll fill up with the straight 40 engine oil that I've got in stock

[Foghorn]

My 1951 B31 does not have a level plug in the gearbox. When I need to top up the oil there I drain it all out and after replacing the drain plug, I pour the correct amount from the manual into a clean bottle and then pour it in.  After that I put a screwdriver down into the gearbox to see where the oil comes to on the screwdriver.  I then draw a pikky of what I found or otherwise write it down and put it in my user manual.
You do not have to replace the oil that comes out if it is good/new/within its service time etc- just top it up.
I gotta admit though, I do replace it generally- better to be safe than sorry.
Foghorn.

[V500]

Just do what a million commuters did back in the day, and slop a bit of oil in when you think of it (if it leaks, obviously)