As it turned out, the two principal BMW Butler & Smith team bikes did not break in that inaugural 1976 Superbike Production race on Daytona’s high banking and infield road course, thank you very much. Though B&S’s third R90S DNF’d under Gary Fisher—“Fish was a little brutal on machinery,” says Reg—Pridmore and McLaughlin went the distance, running wheel-to-wheel most of the way. Loudspeakers blared Reg the winner—but a high-speed finish line camera proved McLaughlin had crossed it first, winning by mere inches. Reg had been leading the final lap until the kid nipped him at the wire.
Those BMWs weren’t stock!
BMW’s 1-2 finish at Daytona in front of third-place Cook Neilson’s Ducati lit bright lights for the German marque and tuning savvy of Butler & Smith. Surely, however, those BMWs weren’t stock. What modifications had been made on the R90S, and what was it like to ride the new boxer race bike?
Mods first. On the basis of their experience building BMW F1 bikes in the early ‘70s, Butler & Smith engineer Udo Gietl and fabricator Todd Shuster went to work modifying the R90S originally conceived by Hans-Gunther von der Marwitz, while Rob North contributed his own frame design wizardry. The two-cylinder M04 engine was uprated with shortened connecting rods and displacement punched out to a loose-rules 1,000cc. Breathing through 38mm Dell’Orto carburetors and fired by twin spark plugs, the modified M04 served up a healthy helping of torque and almost 100 horsepower (the stock R90S had just 67), enough to be competitive with the four-cylinder two-stroke Japanese Yamaha TZ750s. In conjunction with raising compression, the boxer’s cylinder barrels were shortened slightly, allowing more lean angle in corners.
As powerful as the boxer twin engine became, it had a known weak point in its single central camshaft, supported at both ends but lacking a middle bearing. The long shaft tended to flex at high rpm, and riders had to take special care not to over-rev the engine, even though it was supposed to be reliable to 10,500 rpm. (Stock, the M04’s power peaked at just 7,000 rpm.)
“I ran mine to ten-four, ten-five, and they ran really well. But if you abused them when you downshifted you made the camshaft do things it couldn’t keep up with and it would just break the cam,” Reg says. “They were going to get you to the line, but if you kicked the shit out of them they wouldn’t.”
Handling, of course, was also key to finishing. North’s frame technology, which gave it a brace connecting the motorcycle’s steering head to swingarm pivot, much improved stability during cornering and at flat-out race speeds, but it couldn’t perfect the bike’s overall geometry.