Sunday, July 10, 2016

Sportster Blow By Catch Can

     I hope this catch can will solve the annoying problem of what to do with venting the crankcase.
     The crankcase builds positive pressure that must be vented. When the engine is started, condensation from the crankcase is vented until rising temperatures eliminate any water vapor from the system. After that it's an oily mist that is vented.
     Harley Davidson simply vents the blow by into the air cleaner. The problem is that on long rides oil can drip out through the air cleaner element and cause a mess.
     When I first built this bike and changed the air box, I ran a hose from the crankcase breather bolts down below the frame to vent onto the ground. This didn't work well for me as the hot oily mist condensed on the cold frame rails and made the bike an oily mess underneath.
     Also in my garage, the bike would occasionally drip onto the floor. It was only a drop or two, but I cannot abide oil leaks where there should be none.
     I got a bright idea, put an old fuel filter on the vent hose. The theory was that the filter mesh would condense the oil mist and the oil would sit in the filter body. The only trouble was, it didn't work, all I did was move the oily mess from the bottom of the bike to the top.

     I wondered how much oil came out through the system, so I taped a paper towel around my (fuel) filter to catch the oil. The photo shows how much oil was in the paper towel after a little less than a hundred miles.
     It certainly shows that my engine is not experiencing excessive blow by. It's amazing how much mess a small amount of oil mist can cause.
     I decided to look on the internet to see what others had done with their crankcase breathers. I was hardly surprised to find dozens of different opinions all presented as though they were the most expert advise possible. It seems oil has that effect on motorcyclists.
     I decided that a proper catch can would be the best solution to keep the oil mist and water vapor out of the engine and off the ground and bike. Most of the catch cans I saw were automotive and quite large for a motorcycle. I found the one below, made by a company called Golan. It's well made in the USA and seems that it would hold about about an ounce of fluid.