hey Jeff Would really appreciate a copy of the psru drawings I am Fitting a BMW R90S engine to a Texas Parasol my email is email@example.comYears ago, I built a very successful PRSU for an ultralight I still own, using a 1-1/2" wide poly-V belt, machining my own pulleys. It had a cog belt & centrifugal clutch arrangement before that which had several problems: the clutch would slip; so I eliminated the clutch, then the rubber cogs would strip out in a very short time. With a piston engine, the power pulses must be accomadated somehow or something will break, sooner or later. Presently, I am building a Jenny replica and have bought a Geo metro engine to power it with. I have designed a PRSU using a 3- inch wide poly-V belt, a rear axle spindle from a Plymouth horizon car, a 5/8" thick aluminum plate that will bolt to the bell housing bolt locations via standoffs to clear the flywheel and some aluminum pulleys that I will machine myself. I will also incorporate an outboard ball bearing to eliminate overhang loads on the crankshaft. It is essentially a scaled-up version of the one I built years ago. If you are not familiar with what a "poly-V" belt is, it is the same as a serpentine belt used on new cars, except a lot wider. It allows the system to slip a tiny bit, easing the pulse loads. On the first PRSU I built back in the eighties, I bought 2 belts, to have one as a spare, I still have the first one on the machine, the second one hasn't has been used yet. I could probably send someone the drawings if they're interested and have access to a lathe.