My first thought is that the oil might be coming from the primary, leaking out at the felt 'seal' between the gearbox and its sprocket. Oil can drain from the crankcase and into the primary, then it gets flung about as the clutch turns and leaks out of that seal behind it. I learned that one personally! Would it do that enough to empty the oil tank? Not sure. Undo the level plug and see what comes out.
When it was running you'd have noticed lots of blue smoke if the crankcase was filling up (as would happen if your oil pump return had given up), but there doesn't seem to have been that much oil in the crankcase after you checked. An eggcup full is a decent amount, as you noted.
I discovered my primary-to-gearbox sprocket leak when I put ATF in the primary and the color of the drips told me all I needed to know!
Even so, the first thing to check is all the joints in the oil feed line to and from the oil tank.
Hi Allan
many thanks for your helpful reply.
I checked the primary oil level and it was just below the level plug so I am guessing engine oil is not disappearing into there.
I'll check the preesure release valve and one way valve in the pump pick up pick and double check oil pipes.
It may have been an issue for a while but hammering it up the M1 on the hottest day of the year on 40 grade oil may have exacerbated it. It ha soften leaked a bit on parking up and I'd convinced myself this was from the gear box but yesterday on checking its still pretty full.
I am going to follow up your advice on oil in the primary and do a double check
Well so far the only likely culprit is the mag pinion seal. This was extreemly sloppy with about 1/16" gap between the pinion shaft and inner seal lip.
I was entertained a couple of weeks ago by the sight of the magdyno bouncing up and down when the engine was running so not doubt that did for the seal. Awkward size to find from a mainstream supplier (Simply Bearings).Russells reckon they have them but I'll have to wait 'til after the bank holiday to confirm
