Motorcycle Repair: Oil through the crankcase breather, honda cx500, crankcase breather

Question
I know you don't want questions on any bikes other than those you specified, but I have a '81 Honda CX500 which has started leaking a thick, creamy-coloured 'oil' out of the air-box. It occurred after I had gone on a relatively long ride (50km). I have drained the oil and found no water or particulate matter, and the level has been constant. Is this likely to be a serious engine problem?

Answer
Some bikes have a drain tube on the airbox because of this phenomenon. If you use the bike for short distances typically, (and 50km is a short distance) then there can be some moisture or fluid that collects in the airbox.  This also is related to the humidity in the air.  If you look at the engine, you will notice that there is a crankcase breather tube that goes into the airbox.  If there is a little compression blow-by, i.e. if the rings are a little stuck, some of the compression will get past the rings and cause a positive pressure in the crank case.  As the engine gets hot, the water that had been in solution in the oil will come out into the crankcase area, and be pushed out of the crankcase vent.  This is usually an oily, creamy fluid.  Take the bike for a 150 mile ride and this issue should be solved.  Once the oil is really hot, the water will have come out, or if you have changed it, you should also notice an improvement.

This is why the oil level on bikes that are stored, goes up.  Oil will take on a large percentage of water, and this is bad for the lubrication system.  This also explains why the oil level on a bike that was stored will typically drop when it is used for a good ride after storage.

Good luck,  Jan