In the Whack-a-Mole world of hunt the oil leak Ive managed over the years to eliminate most of them for at least a few miles but one of the last has eluded me for years.
I've traced it to the gearbox seal area but having replaced the seal and sprocket and taken a lot of care in the area I have discovered that it is actually passing between the inner shaft and the outer shaft of the gearbox dual shaft. I can detect no lateral of longitudinal play.
I understand and can confirm the shaft has scroll grooves which are supposed to channel oil back into the gearbox - but that is only possible when its spinning.
So I am wondering if it is simply that I am overfilling it!
My BSA handbook says oil capacity is 1 pint. I note that this brings the oil level up to the inspection hole if not slightly more when the bike is on its main stand. That is certainly about the level of the output shaft.
Can anyone confirm that 1 pint is indeed correct or is this for the post 54 type gearbox.
My model has no level plug only a drain plug. The later type has a level plug at the rear (my '54 model A10 had that type).
Appreciative nod in anticipation.
Chris Barrable
Hi,
Here is the useful data sheets covering the years in question:
Best wishes...
Thanks for the image of the spec sheet. It matches mine saying the gearbox capacity is 1 pint so definately up to the brim of the inspection cover.
So the puzzle remains as to how to stop the oil (fairly thick EP80) from seeping between the inner and outer gearbox main shaft, onto the sprocket and dribbing via the chain to everywhere on the underside of the bike.
I guess as a last resort I need to have the gearbox stripped and rebuilt with a new bush. But I believe the bushing is part of the shaft itself.
Any further tips or advice from our wealth of numbers?
Chris
if I recall, the spiral groove in the long (or two short) brass or phos bronze bush is directional. if fitted wrong way it might not stop oil flow.
I hadnt realised that, though the gearbox was rebuilt many years ago by specialist. Im reluctant to strip the box on the offchance, but thanks for the advice.
Oil seeping along the mainshaft is found in other bikes and often worse when the bike is on a side stand.
You may not be able to completely stop the leek/drip. Oil needs to get along the whole length of the bush so it is inevitable that some will escape in the absense of a seal.
There is a sprocket nut incorporating an oil seal for the swinging arm gearboxes. It does not fit plunger bikes. Some unit engines have an extended sleeve gear bush which passes into the primary chaincase to prevent the external drip.
It is worth experiementing with a thicker oil in the box before dismantling. EP90 is thicker than 80 but some owners are concerned about using EP oils in a box with phospher bronze bushes. You could try SAE 50 engine oil.
I use a Morris non EP gear oil in my A10 box.
Thanks. Curiously I've previously used 20w50 engine oil (as specified in at least Haynes) and now that you mention it I've noticed the leak more since I replaced the gear oil with gear oil EP80. I have assumed it being thicker wouldnt increase leaks and I have not heard about EP oil being less desirable but you may well have a point.
I will replace the oil with engine oil straight 50 as previously used to see if that really does make a difference.
Update: I stored the bike leaning away from its side stand & hey presto; no oil leak. Even after a ride there appears little to no oil coming from the gearbox.
I will swap from gear oil to engine oil as previously used to see if that makes any difference.
The fact that it doesn't leak after being leant the other way suggests that it is the oil seeping through when the box is stopped (and warm) when, of course, the scroll seals will do nothing. I think you have found your fix.
probably sorted then, I get a lot of bikes in (modern) with left hand fork seal leaking... normally because they are left on side stand and weight of stanchion (tube) presses on seal lip deforming it allowing it to leak. parking on paddock stand or near upright solves problem.
with regards to BSA final drive sleeves, Drags and others are offering split bi metal bushes for this use, Ive also turned down phospor bronze bushes to suit, both sorts require two bushes with a gap between, the original B40 Im doing now has a single 2 1/2 times longer one with a central recess in the middle and an oil groove around a single turn which goes from the gearbox end into the central recess which drains oil collected in the centre groove back into the gearbox. theoretically, the gap in between the two bushes stops the oil, BUT without the directional groove it does not get returned therefore seeps out. if I had access to a CNClathe I would make the correct ones and probably stop the problem,
I'm assuming that your gearbox does not have the sprocket oil seal (65-3508), I'm not sure when that was introduced but my 1954 box does not have it. If it leaks when on the side stand then oil is most probably either seeping through the main ball bearing (24-4065) or along the pinion sleeve bush(s).
If you ensure the bushes are not too worn and replace the ball bearing with one with rubber seals (take out the inner one) you should cure this (I did). Of course it means taking apart the gearbox so maybe just use the main stand until you have to tear down the box anyway.
Bearing is a 6207 2RS and should cost, at most, a tenner.
My '53 model does have an oil seal on the sprocket shoulder. So am concluding it is seeping along the shaft when meant that side..
I like the idea of a half sealed bearing.
Is there any science in a thicker oil being more "wicking" than thin oil? Oil seems to be able to leak where water doesn't for example.
Hi,
Same problem on '51 Flash. Sealed bearing with on side removed helps with oil seeping around the standard seal but not the seepage along the main shaft. However, SRM do a gearbox sprocket nut with a seal built in. I believe that they are universal so should fit. Not an easy job on a the plunger box as it needs to come out of the frame but perhaps have one ready next time the box needs to come out.
Dave.
I think the SRM sprocket nut with seal is only for swinging arm models,
from their website:
A new SRM product , this stainless steel gearbox sprocket nut with oil seal, will help reduce the oil weep from the gearbox mainshaft when the bike is standing on its side stand, a most annoying leak that affects many bikes.
Note it only fits BSA pre-unit swingarm models A7 A10 B31 B33 and Gold Star models gearbox.
Sorry does NOT fit any plunger model.
I found a DIY solution to a similar problem with the M20.
1. Obtain margarine tub.
2. Remove lid.
3. Empty contents.
4. Place empty tub under machine. Note; it is important to check that the centre of the tub is vertically aligned with the oil drip point.
Occasional maintance : empty tub when approx half full.
;)
I'm no expert, but I'm considering trying Dean's clever fix on other models. Or would it only work on an M20? ;D
thank you for all the informative tips, some long term fixes and some more Heath Robinson .
I am choosing a variant of Dean's suggestion as my overall Top Tip !!
A very late response to an old problem! I also own a 1953 M33 (recent purchase and still getting to grips with the foibles of BSAs and their oil tightness...or not!). I've stripped and rebuilt the gearbox, replacing bearing with modern sealed bearing, retaining the outer side seal. On filling the box with the required one pint and running the engine, oil immediately starts to leak from the output shaft on to the chain. This stops when the oil in the gearbox has dropped to about 2/3 rds of a pint. Being a 1953 plunger model the SRM modified nut doesn't fit. Thickness of oil doesn't seem to make any appreciable difference. Just wondering if there has been any further development with regard to a cure for this issue. Did you ever cure yours Christouring? Either way it looks like the gearbox has to come to bits again!
GeoffRS
See this post:
https://www.bsaownersclub.co.uk/bsaoc_forum/index.php?topic=9041.0
A brief summary:
Put 400ml of oil in the gearbox, or fill to about 1.0 to 1.2 inches below the gearbox main shaft centerline.
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.