Mk III Chaincase Increasing Oil Level

Sounds very much like your crank shaft oil seal has failed but the good news is that this can be replaced with the engine in place. There is another thread on here explaining the right and wrongs of taking the old seal out and replacing with a new one.

My advice is to take your time and buy 2 new oil seals. I have seen a few not seated correctly, mostly through rushing the job.

As for your clutch drag, the increased primary level would certainly cause slip but while the primary is apart I would clean all of your plates up. Petrol seems to work well although other plate cleaners are available. I use ATF in my MkIII chaincase.

A rebuilt well lubricated non abused gearbox should be good for more than 20,000 miles, less a spring or two.

Good luck.

Sounds like the crankshaft seal behind the primary drive sprocket is leaking or being dislodged by oil level in cases being to high as a result of the wet dumping issue you mentioned (this is a common problem associated with wet sumping). Or oil leaking past the primary case fixing bolts.

It's is also possible the clutch plates my not be separating cleanly and "gummed" up due to excessive oil in primary case.

Either way time to strip and investigate the contents of the primary case.

The Mk3 can be a bit prone to this and is fiddlier to repair. Rather than a shoulder behind the oil seal, it has a wire circlip in front which does have the advantage of stopping it popping out but it can still spin.

The best method is to clean the aperture very thoroughly (cotton bud with alcohol or similar), use an oil seal with a metal outer and apply a small amount of bearing fit, then gently ease the seal in by lightly pressing on the circlip behind it until it just pops into the groove.

If the housing is damaged (as can occur if a metal seal has spun) then the only answer may be an engine strip and machining for a top-hat bush with circlip groove.

My MK 3 also has this primary chaincase oil build-up problem caused by a leaky crankshaft seal. One of these days I'll get round to the laborious strip down and reassemblingtask of the Mk 3'smultipartprimary drive but for the past couple of years have contented myself with unscrewing the level plug and draining off the surplus every 300 miles or so - havingfour other bikes don't clock up big a big annual mileage on the Mk 3 and clutch slip is never a problem with this routine extra maintenance task.

Some of the possibilities re difficulty engaging 1st at standstill:

Tickover too high?

Notched clutch centre - dragging clutch (or binding due to oil gumming)?

Worn dogs in gearbox?

Your drive side oil seal may well be worn but asking it to deal with a crankcase half full of wet sumped oil on start up is too much. 828cc of compressed air on start will pump your crankcase full of oil, out through every way it can find. The easiest route is the drive side oil seal. What to do? not much actually. Drain the primary drive chain case to the level screw with the bike on the side stand. Thats as much as you need in there. If you know that the oil tank has drained down into the crankcases, then before starting, drain the crankcase into a jug, (make sure it is big enough to take the whole oil tank contents because it might all be in there) and tip it back in the tank. Then you can start as per normal. The Mk111 should be less prone to wet sumping as it has a valve fitted in the timing cover. It would be worth checking that valve out. You may consider leaving the bike with the pistons at TDC for any length of time as there is a theory that this slows down the wet sumping process. Starting the bike once a week should prevent the need for this faff and cleaning the clutch plates off will probably deal with the dragging clutch but you might get away with just the crankcase drain. win win

The MK3 cover only addresses one leak, there is the other where the oil moves from the feedside to the sumpside of the pump through the clearances for the shafts, cure for this is O ring seals installed in slots machined in the pump body. Even then 100% free from wet sumping is not guarenteed.

Give the timing cover (Over where the ball and spring reside) a few sharp knocks with a rubber mallet. Far easier than taking the cover off.