Ever since The Bride went to the West Coast, I’ve missed having a CVT-equipped bike to toodle around on. So, I’m jumping back into this pond.
Like The Bride, this one will combine a mini-bike-ish industrial engine drivetrain with a full-size motorbike frame. I knew I didn’t want to do another 6.5HP Predator/GX-clone. Looking around at what’s available online, I ended up waaaay down the diesel bike rabbit-hole. I decided to attempt a Yanmar-clone-powered build. Unfortunately, going even just a few rungs up the displacement ladder, diesel engines quickly get very heavy and very expensive. So, I set my sites on a decidedly modest performance spec and bought this nice little 173F [247cc, 5HP] Yanmar clone, which is typically used for roto-tillers and cultivators. The cost was $295 in total, including tax & shipping.
For a chassis to put it in, I didn’t have a clear idea of what to do with my moribund Retroblaster project, so I dragged its KTM GS80 frame out and, sure enough, the 173F fits in the engine bay without much effort. In fact, compared to fitting The Bride’s engine in to the Shin Sang Tong frame, or the Ducati Monster engine in the Harley 350, the engine bay is downright roomy!
Unfortunately, there isn’t room to fit a torque converter; the crank PTO is waaay too far outboard, and there isn’t fore-aft room for even a little 30-series CVT without significant mods to the frame. In order to avoid undue complexity, at least initially, I am going with a simple centrifugal clutch driving a jack shaft. That’s not ideal, but with only about 5HP on tap, it’s going to be S-L-O-W no matter how I rig it up. I’ll just gear it down low enough to practically facilitate take-offs, and then see what sort of top speed that gearing gives me. It really won’t matter; I see this as a parade/show/pit bike, not something I’ll license for the street.
Obviously, I have additional chassis parts from the Retroblaster that I can use to cobble together the rest of a rolling chassis, but the big 120/90-18 tires and triple-disk brakes originally earmarked for that bike would be weighty overkill for this. For wheels, I am going to stick with “real” motorcycle parts, not donut wheels, but the gearing challenges of a single gear ratio mean the smaller the wheel diameter, the better. I have chosen matching 16-inch Suzuki cast rims, circa 1983 (GS300L rear, GS550L front). Both are 2.15″ (WM3) width and will take the same 90/80-16 tire size front and rear.
I’m motivated to keep Bultakenstein on the front burner right now, but it’s good to have the ability to change things up every once in a while.