Annoying A10 gearbox minor leakage

[EDDIE SIMPSON]

Hello ,
Has anyone permanently cured the gearbox tendency to weep oil onto the drive chain and run down the primary inner case to the floor. I m sick of the black patio oil spots(well my wife is) after a run.
I know it's the gearbox as I do top up the gearbox with sae50 but primary level stays constant.
Seal is about 5 years old and I wonder if it's up to the job?

[JulianS]

Maybe coming from the sleeve gear bush along the main shaft and dripping out. Triumphs do this and worse when the bike is on the side stand.
SRM do a gearbox sprocket retaining nut incorporating an oil seal which keeps oil in at this point.

[EDDIE SIMPSON]

Hi Julian,
Does your A10 leak any gearbox oil onto the drive chain?
I have seen these bushes worn but mine were good to go on assembly.
I just can't imagine the majority of oil coming out this way, but I may be wrong. I suspect the main seal is a poor design but wanted to know if others had gearbox leaks and now have leak free zones.

[JulianS]

Before the SRM nut some oil from the bush ran down the outside face of the gearbox sprocket and onto the chain.
Sometimes the main oil seal may be difficult to fit because the outside diameter is sometimes just a fraction too large for an easy fit over the main bearing causing a problem.

[limeyrob]

Keep a tray handy, these are 70 year old bikes that were never oil tight when new. It wasn't common practice to fit oil seals (ie the kick start and gear lever bushes), the philosophy was if its oily it will last, and 70 years on they were right.  Are you topping to the level screw?  Could some of the oil be from the engine breather?

[EDDIE SIMPSON]

I have found oil from the breather will drip rather than weep out . I will have to try the SRM gearbox nut as well as the inner chain case oil seal upgrade.
I take it your A10 s are oil tight?

[JulianS]

A simple and effective (and cheap) felt seal on the clutch centre will help keep the oil in where it enters the sliding plate. The one in the photo came with an SRM clutch I fitted some years back.

My A10 gets some drips from the engine breather which has an extension tube on it. Other than that it keeps most of the oil in.

[limeyrob]

Mine is far from oil tight.  No big leaks as its all rebuilt but there's always a slight film and a drip or two. My bug bear is the breather and I'm keeping a watch on that.  I've never had a oil tight chain-case so I always carry a rag in the tool box* Being old enough to have bought a BSA new in 1972 we didn't expect oil tight from any British bike, it was a shock when mates bought Japanese bikes and they didn't leak a drop.
*Remember those pressed Norton cases with the single rubber seal, they could hold the oil in for about 20 miles, or the BSA C 10,11,12 with the pressed primary and that long cork gasket and all those little screws?