The fluid drive was an important part of Charlie Fehn’s invention. It is featured in his 3,268,025 patent. He referenced 2 fluid drive patents in his patent. 2,357,338 is very technical (boring) and details the internal fins inside the fluid drive. 2,445,058 shows the fluid drive engine mounted on a Doodle Bug minibike. I suspect this is where Charlie got the idea to mount the fluid drive on the MK0 engine. The drive on the minibike works without a hand clutch. The fluid drive on the MK0 needs the clutch since it does not slip enough to work like the Albion mounted fluid drives on my MK1 bikes. My first MK1 works best filled to 10:30. My Rust Bucket MK1 is filled to 11:00 and needs about a minute of hard riding before it grabs enough to take a steep hill. I have the MK0 filled to 9:00 (half full) and it still does not slip enough to ride without the hand clutch. Steep hills are no problem with the MK0.
My previous experience with fluid drives was in manufacturing plants where fluid drives were used between an electric motor and a variety of heavy equipment. I see they were also used on Simpson washing machines in the late 1950s. The MK0 fluid drive has a 17 tooth #35 chain sprocket on the engine side.
There is a one way bearing inside the fluid drive that allows kick starting through the Albion gearbox. I don’t want to wear the one way bearing out so I have been using my recently rebuilt Fairbanks Morse recoil starter which is already showing signs of failing. The engine is still difficult to start with the recoil so I may swap out the fluid drive for a 17 tooth sprocket until I can go through the engine and swap out the two .032″ head shims for a pair of .062″s. I have a couple years experience riding Rokons with handclutches. Once I have the engine starting easier with the recoil I will put the fluid drive back on. The 82001 engine is also wearing out the Albion kickstarter.