Now that the Aermacchi–Ducati divorce is final, what options do I have for the chassis going forward? Well, if you look at the frame’s long, squat engine bay, suitable options are limited. There’s not a lot of room for a vertical cylinder, and those longitudinal frame tubes are too close together for anything to extend upwards in-between them. Any engine small enough to fit vertically and has an integral transmission will be much too short. The motor would either need to be located either way to the rear of the cradle, or situated with the output sprocket way too far from the swingarm pivot if it’s placed further forward.
So, I could think of five other possible non-Ducati options. One of them I’ve already discussed.
- A small, lightweight engine with a non-unit transmission. I’ve thought a number of times about building a bike around the engine and transmission out of a Polaris 250 Trailblazer or Cyclone ATV: a small, light weight, tractable, air-cooled two-stroke with a CVT torque converter. Given my positive experience with The Bride, this idea piqued my curiosity. My first investigative step was to spend $40 an empty crankcase and inner primary (er, clutch…er, transmission) housing. What I discovered is that the size of the CVT a potential issue. The Polaris engine itself is not a problem. It’s admirably compact, but as a result of the CVT case’s size, the crankshaft would have to sit very high in the frame—so high that there might not be enough room for the top end. Of course, as a two-stroke, there wouldn’t be much to prevent me from rotating the engine so that the top end would be inclined. But it’s back to a crapshoot: depending on the transverse offset required, it might fit, or it might not. Or be technically do-able, but undesirable. Sound familiar? So, scratch this idea. At least it only cost me $40 this time.
- A GY6 150cc scooter engine and CVT. I already discussed the Italjet Amarcord in an earlier post, so I won’t delve too deep into it here. The final verdict is a no, anyway: just as with the Monster and the Trail Boss drivetrain, the length of the scooter powertrain unit would be borderline possible fit in the Aermacchi frame. And then I’d have to fabricate some sort of final drive off the rear wheel spindle, which would then require a different rear wheel with a right-side sprocket carrier. And when it’s done, the result is worse performance than a Chinese scooter.
- Some sort of non-unit motor. The added length of a separate transmission housing would help fill the frame, and a chain primary case would be much narrower than a CVT hanging off the side of the bike. The compact, lightweight, simple Polaris engine could still be a candidate, but what transmission? I hate right-side shifters, so nixes all the traditional British gearboxes. That leaves a ’90s-’00s Enfield 500 Bullet and Harley big twins. The Bullet’s transmission and primary case seem a more suitable match to the 22 horsepower Polaris, but either option would take significant work to marry the Polaris engine to. I’m not sure I want to take on all that.
- A Honda clone pit bike motor. Definitely no clearance issues here. Unfortunately, we’d have the opposite issue, aesthetically. Even with the horizontal cylinder, the engine’s diminutive scale would have it swimming around in an engine cradle clearly designed for something larger. And, as with the GY6, that motor would be saddled with a lot of extra chassis weight to lug around. The options on the market are either a 110–125cc semi-auto clutch version pumping out something south of 8HP for about $350, jumps up to $700–800 for a 15HP, 140cc model, and on up to a price tag well into four figures for a 25HP four-valve’r. The power-to-weight-to-cost equation isn’t ideal anywhere along that continuum. Let’s skip this one as well.
- An Aermacchi motor. With all these mental gymnastics, figuring out whether this or that engine could fit this bike, the obvious answer would be to just get one that it was made for. Well, duh. But here’s the thing: I don’t really want an Aermacchi engine. I love them, but I don’t want to own one. They’re temperamental, difficult to work on, hard to get parts for, expensive, and just plain old. I’ve done old, and had my fill of it. Supposing I found a good-running 350SS/SX motor for a decent price (a tall order), I’d then have a nice vintage Aermacchi with non-standard bodywork and modern wheels. Why not just go for a stock Harley 350?
- And, finally, we come to my last idea. Do you know what else that extra long engine cradle would be ideal for? A whole stack of batteries and a meaty mid-mount electric motor. Yep, that’s what I’m thinking. This would be a great electric bike project for somebody. Not me, of course. I have no aspirations of building anything electric. I don’t have the first inkling of how to design, construct, tune, or maintain an electric powertrain. The little I do know about them makes me think they’re expensive, horribly complex and time-intensive to fabricate and get running, and that I’d have a significant chance of dying from electrocution.
All this is to say that I’ve listed the bare rolling chassis on my local CL again, and dropped the price to $350. Maybe some EV wiz out there is looking for a great starting point.
