Sometime ago a member of my club who also has an WM20 had decided to carry out a modification where by he vented the oil/vapour from the crank case breather directly into the primary chain case via a rubber hose.
He said that it stopped oil from dripping out onto the road when riding and when the bike was parked after a ride.
I decided to do the same modification to my bike but have noticed that moisture is entering the the primary case via the engine breather.
I understand that an engine produces water because of the combustion process.
Can some one explain why the moisture is entering the primary case from the breather yet the oil tank shows no sign of moisture/water?
The oil in the primary case does not appear milky.
Where I live it is winter and I have recently ridden the bike in heavy rain on a couple of occasions.
Also because I have quite a few bikes it can be many months before I ride the WD M20 which just sits in a shed.
Does this indicate that an engine over haul is required?
Any water vapour in the oil is evaporated by the heat of the oil in the tank and engine. But the mist that goes to your chain case is cooled so water condenses out. Cars in the days of carburettors were always clogging up their air filters with white oily rubbish because the engine breathers were fixed to the air filters.
Breathing into the primary chaincase was a mod carried out on at least one pre-war works competition machine with a similar set up to the WM20, so presumably thought to be a good idea. Moisture will inevitably be present as explained by Ian and also because water can get in at the back of the clutch. My remedy is to regularly monitor the state of the chaincase oil and if it becomes contaminated drain, flush and replace. Oil quantity is fairly insignificant and if you really want to economise use engine oil from your last change. Lubrication is only for the primary chain and the cush drive. I've done this for 40+ years with no problems.