January 2020

This bike had been behaving very well since its previous work except for a fairly copious oil leak which was emanating from beneath the clutch cavity. It was engine oil so it seemed logical that one of the oil seals from the primary outer chaincase was not doing its job. This would either be the clutch pullrod seal or the clutch drive seal, and as that was far the larger of the two my money was on it as the culprit.

Otherwise the bike did everything rather well, although the spark plugs were still a bit sooty and it was hard to tell if it might be fuel or oil related. Or both. Looks nice though.


Primary oil drained. Footpeg removed. Clutch cover removed and cable and pullrod released, then outer cover off. Everything looked to be clean and in good shape. Primary sprocket and cush drive nuts were very tight, as you would want, but they came off ok and everything came apart in a most agreeable way. I'm liking it so far.


Inner cover now removed with no drama, and the clutch came out with a lot of oil apparent on the outside of the cover plate, so the oil was indeed coming in via the drive seal. On close inspection, the seal had moved out of its housing slightly, but was also a rather loose fit on the cush drive extension.

I spent a lot of time cleaning all the cases up and removing old gaskets, then after completely removing the seal I mounted the cush drive sprocket inside the two cases so that I could ascertain the condition of the two needle roller bearings that it spins between. They seemed ok and still fit for service. I just wanted to be sure that the seal had not been unable to cope with too much side play if the bearings were worn out.

Decision was made to replace both of the suspect oil seals anyway, along with the now disturbed gaskets, an oil pump o ring and a missing tab washer. The clutch hub would get a smear of grease as it was obviously dry and slightly rusty. I refitted the oil pump drive gear and whizzed it around to drain the sump, as oil was leaking out through one of the threaded holes in the crankcase. Did not take very long, and I was able to see that the oil light would go out in only one complete revolution of the pump. Nice.



Progress to 8 January 2020.