I'd like to hear about the copper gaskets in the
racebikes, please?


OK, but I warned you it was boring.

And you'll need to do some digging in old bike books. find a photo of the Butler & Smith R90S superbikes that ruled the AMA Superbike class in 1976. They were Daytona Orange, and were ridden by Steve McLaughlin, Reg Pridmore and Gary Fisher.

Look carefully at the side photos from Daytona. You'll see an aluminum plate behind (inboard of) the carb, which curves outward in front of the rider's feet. he plate looks as if it is there to direct airflow to the carb throat in some magical and esoteric fashion.

Not.

The motors were 1015cc displacement, achieved by boring the cylinders to 95mm, or more precisely, 3-3/4 inches, which was the size of some nice, light Venolia pistons that we sourced. The connecting rods and cylinders were shortened, too, but that's not gernmane to this already long and boring
story.

Trouble was, the biggest motor that BMW made then was the R90, which had 90mm bore. Thus the biggest head gaskets had a 90mm hole in them, which was a little small for our purposes. So we sourced some lovely annealed copper gaskets, micropolished the head and cylinder mating surfaces, and off we went to the races.

After the firat day of Daytona practice, it became evident that we would need the hand-formed aluminum deflectors behind the carbs. Airflow wasn't the issue.

Oil on the rider's boots WAS becoming a problem, though, as they couldn't keep their feet on the pegs.

A visit to the factory just after Daytona uncovered the first news of the impending release of the 1000 CC models, and the correspondingly larger head gaskets. A backdoor gift of a box of the new gaskets spelled the end of the boot-lubricating copper gaskets.

Please don't tell me how we could have solved the trouble with this or that sealant. The problem is solved, 27 years ago. The trouble with putting 105 HP through a BMW boxermotor is that everything wiggles, shifts and moves, including the heads on the cylinders.

Told you it was boring.


Gee, Tom, are you ADMITTING to obtaining 105 horses? at 9000? (9200?)... at the crank ...or wheel?

Udo recorded 105 on the 1015cc motors at the crank, using a water dyno, turning 9300 RPM redline.

He had 108 out of the 750 motors at 10,500 rpm. but they wouldn't finish races, and the torque and HP were not linear enough to be useful.

By the time I began working at B&S, the Norwood police dept had made it clear that the dyno was NOT to be used again. The test pipes made over 118dBA, and caused severe pain at 50 feet. They would wheel the dyno rig to the back door, open the door, and stick the pipes outside. Dyno testing would start when the last "front office" employee left for the evening.

i heard the dyno run once when I stopped by to visit before i worked there. Very scary stuff. Nobody knew if the motors could stay together.

-Tom Cutter

(originally posted to the Airheads list)