Off-road Special

By Paul Brodie

 

My dirtbike started formulating in my mind when I realized my 1984 Honda XR350 was the most complicated motorcycle I owned: 2 carbs, 4 valves, 8 rocker arms, and overhead cam. It also weighed 285 pounds! Simple is almost always better, and lighter.

I took another 65H frame, cut off the rear and began fabricating. Just then, a friend came by and dropped off 1984 XR200 wheels, swingarm, and rear shock. His timing was impeccable! I’d already located the Sachs leading link fork in San Diego, so the bike began to take shape over the winter of 1999.

The XR swingarm was shortened a couple of inches, and I fabricated a shock mount based on the old Yamaha style of monoshock. I was hoping for 8″ of rear wheel travel, but that would have involved linkages, and got way too complicated, so I settled for 7″.

The gas tank came from a BSA B50. Other details: Acerbis hand guards, carbon fibre seat base, 4-speed transmission, gearing 15/39, 520 O-ring chain, removable sub-frame, 56″ wheelbase, 11.5″ ground clearance, and “desert camo paint”. Weight is 240 pounds. Feet up slides are no problem!

Aermacchi off-road by Paul Brodie

Riding my dirtbike for the first time, it became very evident the front forks were severely lacking. The two shocks had zero oil in them, and the springs were too soft. Further, my inexperience with leading link forks had led to a huge oversight> I hadn’t realized the wheel goes up AND so far back, so at full travel the knobbies would hit the allen screws holding on the tappet cover – not good! You just don’t want the wheel to stop rotating when landing off a jump.

I had a pair of freebie Honda 185 forks, so they got installed. That was a lot easier (and cheaper) than ordering new shocks, plus the Honda forks had more travel and were easily adjustable. The longer forks did raise the front end quite a bit, but now I could ride it. And it’s fun! I enjoy the broad powerband, it’s very tractable. It slides well, and the rear suspension works well for 7″ of travel. The pegs are too high and back too far, so that needs attention. The exhaust note is great from the small megaphone/fiberglas pack/supertrapp disc/muffler combo.

The Honda 185 forks soon showed their weaknesses> they’re spindly and the small drum brake is almost useless. However, I now have a set of 1984 XR250 forks which are much nicer AND have a disc brake. This is great, except they are missing the master cylinder, brake hose, and caliper. Anyone? I also have the XR250 swingarm, shock and linkage, so when I get time, I plan to raise the rear of the bike and give it 10″ of travel. Moto Aermacchi!

The PVL ignition gave a modest increase in performance. I also want to raise compression slightly, put in a stronger cam (probably an “N”), open the ports a bit and mount a 32mm Mukini I have on a shelf. Can you say Roostertail?

Aermacchi dirt bike

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