Riding the bike
Having written about the Bartol 250/350 project during my early days as a GP reporter, it was very satisfying to finally ride one, which, thanks to Manfred John and his Klassik Motorsport organisation team, I was able to do in practice for the Franciacorta round last year.
I found this tweaked incarnation gives a much greater spread of torque than expected from a 37-year-old rotary-valve engine. Before the development of exhaust powervalves, these had a very fierce transition into the power band, and a narrower spread of power and torque, with more power than a piston-port or reed-valve design.
Instead, the Bartol 250 offers the best of both worlds, because there’s a strong, smooth transition into the rotary-valve motor’s strong powerband above 8500rpm, as well as the torque delivery I’ve only experienced before on a twostroke 250 from a powervalve-equipped motor.
During my three 20-minute sessions on the bike I had several drag races out of the Franciacorta hairpin with later 1990stzyamahas and despite my extra weight compared to a typical 250GP jockey, the Bartol kept up with them.
In my fififirst session I ended up having a great battle with a well-riddentz250, whose rider was braver than me on the brakes going into the infield section of the track, only for me to be able to outdrag him out of the slower bends.this was despite the gear-lever being a fraction too low for me to shift gear properly on the brakes, so I would occasionally enter a turn one gear higher than I had intended. For all the wrong reasons this underlined the forgiving nature of the Bartol’s motor – not a term you usually relate to a rotaryvalve motor – as well as the great grip from the Avon tyres as I cranked the bike over further than intended to cope with the extra turn speeds.
For my second session Alistair positioned the gear lever better for me, so I was better able to start riding the Bartol in something approaching anger.third time lucky it all came together, and I could really appreciate the qualities of the Bartol motor – as well as the Bakker frame. It was stable round Franciacorta’s fast sweeping right-handers, and nimble handling in the infield turns.the Bartol braked well, too, the twin front Brembo discs with their Serie Oro calipers stopping the 104kg half-dry bike and its rider very capably from fifth gear down the pit straight.
But the real star of the show is that excellent engine – in my last couple of laps of my third session I inched closer to a 1990STZ250 with its later V-twin reed-valve motor complete with powervalve. I can confirm that the rotary-valve Bartol was the equal of this 10-year younger motorcycle in a straight line, as well as just as strong on acceleration out of a slow turn and a third-gear sweeper.
Mission accomplished,
Harald, and kudos to Alistair
Taylor and Leif Nielsen for helping to prove the value of your engineering skills 37 years