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[Graham43]

Thank you all for your helpful replies, yet again this forum has proved its worth. Good video too, even if it wasn't the same bike as mine it just shows how a small, apparently, insignificant part can cause a lot of problems. I have checked the oil level and I made a new dipstick following advice given in a previous post. Off to the garage now to do the 'draining the chaincase' test.

[Paulk]

Graham, Could you clarify - Crankcase breather on top of oil tank which originally connects to the catch can or chaincase breather comes out of primary chaincase in front of gearbox sprocket(from memory).

[Graham43]

It is the small breather tube coming out of the top inside face of the primary chain case. I do not have the 'standard' catch tank on this bike.

[PeteF]

OK Graham. Interesting as the video about the quill seal is, this is not your problem if the problem oil is coming from the primary chaincase breather.
The chain case should be sealed from the crankcase by the crankshaft oil seal. If this has failed, engine oil will be blown from the crankcase into the chaincase.
That chaincase breather should breath very little if at all.

[Graham43]

Thank you PeteF. I will look at the seal. Perhaps put a catch tank on for now and watch the oil level. Made the job hard for myself by having a sidecar on that side!

[Paulk]

Graham, when the motor is ticking over can you feel a pulsing of air from the chaincase breather? As Pete says there should be no direct opening between the chaincase and crankcase.

[Graham43]

PeteF and Paulk. I have a clear tube on this breather and can see movement of oil mist along it. Looks like the crankcase seal?

[Graham43]

I have been looking into this and I find that I will need to completely strip the drive side, including removing clutch and magneto assemblies and engine sprocket to get to the oil seal. The oil seal seems to be under sprocket covering the bearings. Is this correct?

[PeteF]

Yes, complete primary strip so make sure it is leaking before you do it.