Oil leak

[Phil C]

I haven't yet taken off the gearbox sprocket to have a look at the oil seal there (waiting for socket wrench adaptor to arrive), but I was just sitting in my armchair wondering what else might have caused the leak. I wonder: could it be anything to do with me recently having removed the gas tap from the oil feed line (it was fitted by the previous owner because of a wet-sumping problem) and replacing it with a straightforward pipe? (I decided to put up with the wet-sumping rather than risk forgetting to turn on the oil tap.)  Phil.

[JulianS]

I dont think just removing the tap in the oil feed would cause your leak.

Looking at the 3 streaks of oil on the back of primary chaincase I would check that the alternator cables are a good fit in the  rubber grommet and if in doubt a dob of silicone, that no oil has been passing along the chaincase screws at the top of the cover -  tell tale being oil on the screws when you removed them.

If not already fitted I would replace the chaincase screw in plug with one with baffled breather, or drill a small breather hole in existing one. You can get a bit of pressure in there especilly if the chain oiler is blocked.

[Phil C]

Thanks Julian.

Re the wet-sumping, I'd read somewhere about a leak via a breather, but I guess that doesn't apply with the B40?

I am slightly concerned about the chaincase screw which holds the chain oiler. The screw goes all the way through a clearance hole in the chaincase and screws into the oiler on the inside of the case.  The oiler spout appears to have been squashed so that nothing, or very little comes out of it, but I wondered about oil finding its way along the thread and out between the joint of the oiler with the case.  I guess I'll at least fit a fibre washer under the oiler.

Of course these things don't really seem to explain why I went from no leak to a substantial leak so quickly.

Phil.

[JulianS]

Too much oil in the sump after wet sumping can result in it being pumped out of the breather. Usually stops when the sump is cleared of excess after a few minutes running.

Presuming your bike has clutch lever on the timing cover then the breather outlet is right next to where the clutch cable fits in its seating on the inner timing cover.

[Phil C]

Yes, that disappears out of sight up behind the battery somewhere. Where would it normally go to?

[JulianS]

I aim breathers at the chain and away from the rear tyre.

[Phil C]

I guess I need to follow my breather pipe to see where it ends up. Maybe wet-sumping and the breather tube could explain my leak?

[Phil C]

Searching for my (substantial) oil leak, I have now removed the gearbox sprocket.  Please see photos attached. In order to inspect/replace the oil seal, obviously I need to remove it. How do I do that?

The sprocket's surface which runs in the seal looks slightly pitted, as you can see, but I wouldn't have thought anywhere near enough to cause a leak such as I have, and which appeared suddenly.

Phil.

[Bles31]

I pulled mine out with one of these. When I refilled the box I left the oil around 0.5" below lip of the filler cap. My measurements (a bit rough to be fair) indicated that filling the gearbox to the bottom of the filler cap meant that the seal was flooded with oil (hot thin oil after a run) . Theoretically the seal should retain this oil  but I think it's not necessary to fill that far (for the short trips I have done this far) and is only inviting a leak. My leakage has dramatically reduced. Others may have a view on reducing  oil level in the gearbox.

https://www.amazon.co.uk/Draper-37439-Universal-Ring-Puller/dp/B000PJCBVM/ref=sr_1_1?ie=UTF8&qid=1531593432&sr=8-1&keywords=oil+seal+puller

[Bles31]

By the way, when fitting the new oil seal  I found its metal housing to be quite soft and the seal particularly difficult to get entered square into the gearbox. May be teaching you to suck eggs but set yourself up with something to drive it in with rather than tapping all round its' circumference. A big socket or piece of tubing etc.
Regards.

[Phil C]

Thanks Bles31.

Regarding the oil level, my gearbox has an oil level tube which pokes up through the drain plug.

Phil.

[ducati2242]

As you are going as far as you are with this I would look for one of thees nuts to ensure that the oil isnt leaking down the large splines of the gearbox cog and thought the nut threads .

[Phil C]

Is that to replace the nut which holds the gearbox sprocket in place?

Presumably it is as well as, rather than instead of, the existing oil seal?

Phil.

[JulianS]

The SRM nut is not advertised to fit C15/B40, it is designed for the Pre unit gearboxes. The seal acts on the 0.81 inch diameter gearbox mainshaft preventing oil seeping out through the bush. The bush is not extended as with the C15/B40 setup.

On your bike the mainshaft bush is extended and goes through the seal in the circular plate behind the clutch. If oil seeps through the C15/B40 bush it drips into the primary case.

It does not seal any sprocket to splines leak. Not designed to. You will see evidence on the outer sprocket face if it does leak there.

You could try a suitable grade of loctite on the splines if there is a leak but it will make a subsequent removal more difficult.

Beware reducing the oil level. BSA indentified a problem with insufficient oil in the C15 box causing squealing and sometimes seizure of the sleeve bush and upped the oil level to prevent. I have attached the service bulletin from 1959.

[Phil C]

Still looking at how to remove the oil seal behind the gearbox sprocket.  The tool recommended by Bles31 doesn't seem to be suitable in that the shaft is in the way (see photo attached.)  Also there appears to be a bearing?behind the seal which I wouldn't want to damage.  Any further thoughts/advice please?  Thanks in advance.  Phil.