I was just getting excited about getting the B31 (1954) finally running again, when I noticed an oil leak. The only thing with oil in it at the moment is the gearbox, and the oil seems to be collecting on the main drive chain before dripping off (slowly). The leak is on the left side of the bike only. The right side is nice and dry. When I replaced the gearbox oil, it had very little left in it, and what was there was really thick and 'green'. I topped the gearbox up to the recommended level with engine oil when I refilled it. I'm guessing there might be a leak from oil seal on the drive side of the gearbox? How big a job is this to change, and what do I need to take apart to get to it? I'm a little worried it may be beyond my basic mechanical skills. Is there anything else it might be?
just another thought, can I use a thicker oil that 50W in the gearbox (an EP90 for instance) to see if that cures it?
I would avoid EP oil, the suggestion is that the additives can cause damage to phosphor bushes.
Try a thicker oil or a non EP gear oil such as Morris AG90.
Is your bike swinging arm or plunger?
Gear box oil EP 90 is the same thickness as SAE 50
Quote from: JulianS on 01 Aug, 2020, 18:07
I would avoid EP oil, the suggestion is that the additives can cause damage to phosphor bushes.
Try a thicker oil or a non EP gear oil such as Morris AG90.
Is your bike swinging arm or plunger?
It's a plunger at the rears. Many thanks,
If you look around you can buy EP90 which is "yellow metal friendly". I have used it for many years with no problems.
Morris AG90 for one.
https://www.morrislubricantsonline.co.uk/golden-film-ag-90-gear-oil.html
Chrisb
Check out this previous post. Maybe you are putting in too much oil.
https://www.bsaownersclub.co.uk/bsaoc_forum/index.php?topic=8337.0
many thanks for the link and the advice above. I will get some AG90 and try 370 ml in the gearbox and see if that helps. I know the gearbox is definitely the culprit since I've drained all other fluids (and cleaned the oil tank) and the chaincase cover is off at the moment too.. Can I use an even heavier oil, if such a thing exists? (Edit: just seen they do an AG140 - might be worth a shot!)
I wrote to Morris lubricants to ask about their AP90 and they said the viscosity is the same as an SAE50 (as Idie suggested). I could try a semi-liquid grease (their K400) which has been used in other classics with problems with seals. Has anyone any experience of this or whether it might work? I'll try dropping the oil level of the SAE50 first and see how that goes.
You must make sure that the oil level is below the main shaft. My M33 has no seal behind the sprocket much like the WD gearboxes. It is ok until I leave it on the side stand for to long then it leaks.
In the link I added above, it indicates that 370-400ml of oil brings the oil level in the gearbox to about 1.0-1.2 inches below the centre line of the main shaft for the older style gearboxes with the round screw on cover on the right side.
This is very easy to check. The bike should be vertical. I use a nylon tie wrap as a dipstick, push it down vertically into the oil, press it against the clutch adjustment bolt (which is at the centre of the main shaft) with my finger tip at the centre of the bolt. Pull out the tie wrap and measure the distance from my finger tip to the oil on the tie wrap.
I use SAE50 in the gearbox.
Do not use grease. These gearboxes are designed for oil and grease will not get into the small oilways to lubricate the bushes. You might get away with it for a while but it is not a good idea.
leaks at that end of the gearbox are usually due to oil passing the non-sealed mainshaft bearing and oil seal (if fitted) or the mainshaft sleeve gear bush.
Do you have a plunger/rigid or swinging arm model?
fitting a sealed bearing and ensuring the sleeve gear bush is not worn shoud fix most problems.
Mine is the plunger version (1954). Is it hard to fit a sealed bearing and can I do it with engine and gearbox in situ? I have basic tools, and only basic knowledge, this being my first classic bike.
Regret you need to strip the box to change the mainshaft/sleeve gear bearing.
I recently stripped and rebuilt my B31 gearbox due to selection problems. It is not a job for the fainthearted. Luckily mine was fitted with a sealed bearing.
The oil leak is due to overfilling the gearbox and as it's not easy to haul a B31 onto its main stand it runs down the bush if left on the side stand.
My suggestion would be to use a block of wood. Roll the back wheel onto the wood then put the centre stand down and pull the bike onto the stand. Alternatively put the wood under the side stand, ensuring it's safe and won't topple over.
It is a BSA, a few oil drips are part of the charm.... Don't overfill it and use the mainstand rather than sidestand. - and I carry a bit of cardboard to place underneath if I am parking somewhere that might not appreciate a spot of oil.
A stripdown of the gearbox can be done in-situ but the better option, and easier in the long run, is to take the box out. If you do decide on that route let me know and I can send you a file of all the info I have collected on working on these gearboxes, instructions, tolerances etc.
Many thanks Pete C for your kind offer. I will take you up on it if I decide to bite the bullet and take the 'box out.
How much is an 'acceptable' leak for a BSA from that seal when standing cold (and not been run)? I'm going to measure the amount coming out over 24 hours.....
I've refilled to 350ml and still some came out last night and left a puddle on the cardboard again!
If it is on the mainstand then the leak should be minimal. The problem is often when on the side stand the oil all heads toward the main bearing and freedom.
I don't know where the oil level is inside the casings when the correct amount is filled into it but I suspect it would be just below the bearing (which is situated towards the top of the casing) otherwise oil passing the bearing would be an inbuilt problem.
I would tend towards using the mainstand and when it stops dripping check that you can see oil from the filler cap. If there is plenty of oil still visible in the box then it is probably enough for lubrication purposes.
Drained everything out and put about 320 ml in the gearbox a couple nights ago and hey presto, no leaking! (on centre stand). With a torch, I can see oil in the box looking down from the filler cap. I think stripping a gearbox is beyond my abilities at present (not even confident I could get the 'box out), so will reassemble the bike and see how much oil comes out when it is running. My worry is oil leaking and coating the back wheel but I guess there will be tell tale signs of that when I run the bike for the first time. Thanks everyone for your advice.
With 320ml in the gearbox, it would be interesting to know what the measurement is between the centre of the main shaft down to the oil level, and compare this with the radius of the bearing.
I thought the oil capacity of the gearbox was 1 pint or 570ml.
In any case I have always assumed that, unless you are stripping the box, there is always some residual left after draining so adding a full pint would probably overfill.
I have always just added oil until it almost reaches the level of the filler cap and not had any problems. Turn over the box a few times while filling to get the oil flowing from the outer cover to the main part of the box - or wait . I have just done a quick measurement on a gearbox, on the shelf, and I reckon that the outer race of the main bearing is about a centimeter (at most) below the level of the filler plug.
I have fitted sealed bearings to my gearboxes so it isn't so critical for me.
I had a similar problem on a plunger B31 I purchased. I established that the oil was coming from between the g/box mainshaft and the pinion sleeve (which carries the g/box sprocket). I eventually resorted to removing the primary chaincase and sliding a 20mm I/D x 2.5mm Viton 'O'Ring onto the mainshaft into the annular vee at the end of the pinion sleeve. The cork and felt washers between the primary chaincase and gearbox firmly press the 'O' ring against the end of the pinion sleeve. I've done a few hundred miles since with no sign of a leak.