I got the steering stem back from the machine shop, and I actually gave them all the right dimensions to make it work.
Here you can see where the diameter was turned down, and the spacer collar made to fit the original bottom bearing surface. $140 worth of machine work on a nearly worthless part.
Another view of the machined stem. I instructed the guy doing the work to give it a tapered transition in between the two diameters, theoretically to avoid a stress point at the sharp corner, but thinking about how the forces are distributed, I don’t think it will really be an issue.
The original Suzuki top and bottom bearing surfaces are unchanged, so this could still be bolted right back onto a GS if desired. Although, I don’t know why you’d want to.
The bottom of the stem with the collar in place. I had the lower bearing diameter turned down a bit beyond the collar so I would not have to have it re-machined if my calculations were off and I had to shorten the spacer slightly. Fortunately, it’s just the right length.
And here it is with the lower bearing in place.
Most Bultacos came with 25x45x15 ball bearings in the steering head. There is not a standard tapered roller equivalent that matches those dimensions, so I ordered special Bultaco tapered roller bearings made by Pyramid Parts in New Zealand. When they arrived, I realized that the OD was way too small.
I’d made a really dumb mistake: my frame is a late Pursang motocrosser, which came with tapered rollers stock. The top and bottom bearings are both 25x52x16.5 — standard 30205 bearings I could find at my local Advance Auto Parts for $14.29 a piece.
After thoroughly cleaning the bearing seats in the frame, I tapped the new races into place and was able to test fit the front end for the first time.
I still need to work out steering stops. I actually did this same sort of steering stemmod back in the mid-’80s, to fit a GT250 front end on my old Pursang when I converted it to a roadracer. It worked fine, but I kludged together an embarrassingly weak, sloppy steering stop arrangement for that bike, which ended up hastening its demise. That is why I want to think it through and fabricate it properly this time.
Here you can see the Suzuki WM1.85×19 wheel in place, from a GS850. It restricts me to a fairly narrow 90/90-19 front tire, but that should be plenty for the bike’s displacement and weight.
Heidenau makes their K34R race compound tire in 3.25-19 if I want something sticky, or I can just get a Vee Rubber or Duro “plastic rim protector” for $75.
The handlebars are from a Honda VTR250 Interceptor. I wanted clip-ons with some rise to them, for a less extreme riding position, and they fit the 35mm forks. And most importantly, you can pick them up dirt cheap.
They also help disguise the fact that the fork tubes are a bit longer than they need to be for this bike.