Gearbox oil leak

[Pete C]

I have fitted a sealed bearing as replacement for the sleeve gear bearing (24-4065). That, along with a good condition sleeve gear bush / mainshaft, allows me to fill the box to the lip on the filler port without any noticable leaks. Not worth doing unless you have the box out anyway.

cheers
Pete

[John FD]

I've been following this conversation with some interest as I too have a persistent leak from the gearbox of my 1954 plunger M33. I've switched to 50 monograde from 20/50 oil which has helped reduce the flow. The leaks are small but continuous from the sprocket side and (I think) from the kickstart lever on the other but might be from the gearchange shaft.

Last night I downloaded a copy of the riders Instruction Manual from the club library and was surprised to see that it quotes the gearbox oil capacity as 13 fl. oz (370cc). I've been adding a pint. I had also previously disregarded my repro Castrol lubrication chart, which gives 14 fl.oz (or 398cc), as being a mistake.

[Jim S]

Responding to John's message, as far as I can tell, there are 2 types of pre unit gearboxes:
Up to about the early 1950's the gearboxes had a round screw on cap on the right hand side for the oil fill. This is what I have on my 1949 B33. Any documents I can find indicate the gearbox is to be filled with 1 pint of oil.
Around 1952 or so the gearbox changed. The oil fill port on these later gearboxes have an oval cover retained by 2 screws. Internally, the shifter mechanism is different. I have found conflicting documents on the volume of oil for these gearboxes. Some documents say 1 pint and some say 14oz or 400ml. My 1957 A7 has this type of gearbox and I put in 400ml and it doesn't leak (much).
I don't know how the internal volumes are related between the 2 gearbox types. If 400 ml gives the same oil level relative to the main shaft for both gearbox types, then for me that would justify putting 400ml in the older gearbox.
Unfortunately I don't have access to the A7 currently due to covoid 19 travel restrictions in Quebec, Canada.

[Jim S]

Here is an update on oil levels after obtaining access to my A7:

The 1957 A7 has a later model pre unit gearbox distinguished by the oval oil filler cover retained by 2 screws. Later model B33s with swing arm frames also have this gearbox. I have owners manuals for 1963 B31-B33, 1963 B32-34 and 1959 A7 which all say fill to 400 ml. With 400 ml in the A7 gearbox, I measured the distance from the centre line of the gearbox main shaft down to the top of the oil level. 2.25 inches.

On the early model B33 gearboxes the oil fill cover is round and is screwed directly into the gearbox. I believe this gearbox is on plunger frame models. Any documents issued by BSA that I can find say to fill with 1 pint or 570 ml which results in excessive leaks.

Combining Bles31's measurements with 370 ml in the gearbox (say 400 ml to round it off) and adding the distance from the bottom of the oil fill hole to the main shaft centre line results in 1.06 inches from the main shaft centre line down to the top of the oil level.

So using the main shaft as a reference between the 2 gearbox types, by putting 400 ml of oil in the earlier configuration gearbox (oil level 1.06 inches from the main shaft centre) it will result in having more gearbox components submerged in oil compared to the later gearbox with the BSA recommended 400 ml. (oil level 2.25 inches from the main shaft centre). 400 ml also places the oil level close to or at the bottom of the lip seal at the gearbox output sprocket.

This justifies to me that 400 ml is a sufficient volume to replenish the earlier configuration (plunger frame?) gearboxes and the level can be monitored by measuring 1.00 to say 1.2 from the centre of the main shaft down to the oil level.

Any comments on the above?

[DAVE BRADY]

Good morning,

The plunger framed A7/A10 and the swinging arm variants that use the same gearbox have the oil level plug at the back of the gearbox as shown in a previous post.  I have always used this to determine the correct oil level for the gearbox and I have never checked to see if putting a measured amount of oil in reaches this level or as is being suspected the oil level plugs are actually set too high.  Next gearbox oil change I must remember to do this.
Also, the use of a dip stick to determine the oil level on later A65s is a pain as if a bit too much is put in then it is not easy to get it out.  I was going to retro fit the the earlier drain/level plug with the height tube but it looks like it is different thread.

Dave.

[Bles31]

That seems like a logical approach and some useful information Jim S. I'm inclined to stick with filling to 10mm below the bottom edge of my filler port, in the "early" box on my B31.

 I'm specifying a level as opposed to 370/400 cc because I don't know how much oil is held in nooks and crannies in the gearbox when it is drained. So when  I drained 370 cc from my gearbox I don't know if there was some left in there, possibly bringing the total to over 370. (It might make a difference to someone who had overhauled and completely emptied the box).

From what you say, and from looking at my gearbox I believe there will be enough oil in there to splash all of the internals. I will, however, add oil  gradually to see where my leak starts. I'll feed that back, but it won't be soon!
I had a bit of a concern that the reduced oil volume might lead to excessively high temperature, but if your A10 is OK with 400 cc then that seems to say that I should be OK in that respect . My next runs, when I can eventually get out on the road, will be pretty short anyway.
Obviously everyone will have to make their own judgement on how to proceed.
Thanks for the information.

[Bles31]

For information, there is an interesting video of a gearbox (later type I think) rebuild on Youtube. Search for "Building a B31/B33/B34 from parts. Episode 8 of many". You can see relative heights of internals.