Rider: Alex Sohn

Class: Heavyweight Production

Make: BSA

Model :Lightning

Year: 1972

Displacement: 650 cc

Top Speed: 108 mph

Modifications/Upgrades: 10:1 Compression, MC forged pistons, smoothed ports, match-bored inlets, BSA Firebird Exhaust, Clubman Bars, Tomaselli Controls, Lights Removed, Airbox Removed, Shortened Forks, Bitubo shocks.

Alex acquired this '72 Lightning 6 weeks before his race school. It had been converted to a "bobber" with large apehanger handlebars, a 4" front brake , TT Pipes and Norton Commando fuel tank. The motor appeared to be in excellent condition and only a top-end rebuild was performed.

The "Before" pictures

Motor rebuild 9.5:1 MC forged pistons were installed in a re-bored barrell. The cylinder head was flycut to remove .020", raising compression another 0.5 point. The ports were smoothed and matched to a pair of alloy carb spacers which were pinned to the head with 1/16" dowel pins. The valve guides showed excessive wear, so they were replaced with new bronze guides. Black diamond valves, alloy adjuster nuts and a three-angle valve seat cut completed the head work. Carburettors are stock Amal 930 Concentrics. The ignition was upgraded to a Boyer-Brandsen Mico-Mk III electronic ignition. Sponsor Rich Boucher donated a BSA Firebird scrambler exhaust system, from which the crossover H-pipe was removed as it was deemed unnecessary for racing.

Gearing For the 2006 season, the stock gearbox and 20/47 gearing was used. For 2007, close ratio 1st and 2nd gears will be used. This should help acceleration out of the turns, as the gap between standard 2nd and 3rd was simply too big and the more powerful 750's would always out-accelerate the Lightning. Also for 2007, the switch will be made to 528 o-ring chain with narrower sprockets. A 21-tooth gearbox sprocket will allow taller gearing for faster tracks like Daytona using a 47-tooth rear sprocket while a 50-tooth rear for tighter tracks should allow better should provide better low-speed acceleration. Ratios can be calculated using this handy little gearing calculator: Download ms Excel Spreadsheet.

Brakes A stock conical front brake was installed. Careful setup and adjustment in addition to a heavy duty cable and industrial high-friction linings made the brake work very well. Critical points are adjustment of the shoe gap with the built-in cam adjusters and proper routing of the cable. The brake still experiences substantial fade under heavy load, but stopping power is quite adequate when a generous amount of force is applied. The rear brake is due to be upgraded with the better linings as well.

Suspension The rear shocks were replaced with 13-1/2" Bitubo units from a late-model Moto Guzzi. At 1" longer than stock, these units reduced the front end rake by about 1 degree. This was apparently not quite enough to remove the excessive amount of understeer at high cornering speeds that was found during the first outing at race school. To further impove turn-in and reduce understeer, the front forks and springs were shortened by two inches, reducing the rake by a futher two degrees. The results of this modification showed its benefits at the first race at Grattan. However, the rough track also revealed that the front end was too soft and the rear had insufficient damping. Close examination revealed that all of the fluid had leaked from the rear dampers, so a complete rebuild was undertaken. Also, the front springs were stiffened by shortening them by 1.75" and inserting spacers of the same length. Both modifications made the BSA handle very well at Mid-ohio, though some softening of the rear suspension is still in order.

Frame After developing cracks around the swingarm/rear motor mount area, the frame was reinforced by adding gussets and subsequently powdercoated. Weakness in this area is a common symptom of the Oil-in-frame BSA's and Triumphs.

Electrical System A simplified wiring scheme was used for the 2006 season. Using no lights, a 1 Ah sealed battery and a MityMax regulator/rectifier seems to have been adequate, though several battery failures were experienced. The analog Boyer Micro Mark III seems to have performed well, but will probably be replaced with a digital unit drawing less current allowing the move to a total-loss electical system. The Veypor data logger is also used during racing as speedometer and tachometer.

Photos

Crude Beginnings	Commando Tank	Lovely Handlebars
Initial Build	Preparing for the first outing	Shakedown Run
Race School	Virginia International Raceway	Ready to go
First time on the Track	Feelin' out the twisties
Going into Turn 7	Getting the hang of it	Hunkered down on the straight
Finishing the mock race	First Race: Grattan '06	The twisties at Grattan
Grattan	Grattan	Persuing A CB 750 at mid-ohio
Mid-Ohio