Reprinted  from
NORFOLK MOTORCYCLES AND PARTS COMPANY
Jct. Rtes 115 & 1A
Box 81
Norfolk , Mass
Dial 384-7555
INFORMATION ON PREPARING A(A-10) DRAG RACER

1. Polish to a mirror finish the Crankshaft - Flywheel and Connecting rods. Polish inside of the crankcase where possible.

2. Dynamic and Static balance the Crankshaft, Flywheel, Connecting rod and Piston Assembly. The balance factor is 65% of the reciprocating weight. See note below.

NOTE: When assembling the crankshaft in the crankcase allow .012 to .014 end play in the crankshaft assembly.

3. PISTONS - 9 to I compression ratio pistons. Turn ¼  off the bottom off the piston skirt.

Webco has 9.5 to 1 CR pistons
The-pistons must weigh exactly alike. Remove material from the inside of the piston that is the heaviest until it is exactly alike in weight to the lightest one. Chamfer the bottom edge of the piston 45 Lap the ptston rings in with Bon-Ami paste.

4. Install inlet valves 1/16 larger in diameter .or 1959-60-61 Super Rocket valves. Concave the inlet valve heads to
 reduce the weight of them and make sure that they weight the same. Turn the valve guides to a taper. (The end that
 extends into the valve port.) Open up the valve seats and valve ports and polish the combustion chamber and valve
 ports to a mirror finish.
 Install S & W valve springs, shinned to 1-5/16 with 185 lb. pressure.
 Set the inlet valve with .010 clearance and the exhaust valve with .016 clearance on iron heads.
 .008 In. .008 Ex. clearance on alloy heads.

5. CYLINDER HEAD: - ---Open up and grind out the manifold and polish to a mirror finish. Lighten the rocker
  arms and polish. Lighten the tappets adjusters and cu -a screwdriver slot in each one. Use spacers place of the
  sideplay springs.

6. Use a Part No. 67-357 or 67-358 camshaft. Lighten the four tappets. Use Alloy pushrods.

7. Lighten the valve gear train.

8. Use l-5/32T.T. Carb.

9. Set the ignition timing 3/8 before top dead center, or 39degrees

10. Use Indge-RL-47 Spark Plugs.

11. GEARBOX: Assemble sprockets on the machine so that you will have an overall gear ratio 4.72 to 1.
It would be a good idea to fit and lap the gears that there will be a minimum drag at the gearbox.

12. CLUTCH: It will be necessary to use the latest re-inforced clutch center and also weld the clutch springs studs in
place.   It will be necessary to use the latest type reinforced chain wheel. It would be a good idea to balance the entire
clutch assembly.

13. WHEELS: Use alloy rims - the lightest tires that can be obtained with a tire that is ground flat on the rear wheel.

14. Lighten the frame as much as possible by removing all brackets and lugs that you wIll not be using. Replace the shock absorbers with alloy struts with holes on l2 ½ centers.

15. EXHAUST PIPES OR MEGAPHONES: Use standard 1 ½ A-10  exhaust pipes with a gradual tapered
megaphone 18 long with a 4 opening.

16. HANDLEBARS: Use the clip on type of handlebars shortened to the limit. It will be necessary.to remove
 evcrything you can from the machine to make it as light as possible and to reduce the frontal area to obtain
 maximum streamlining.
 

BSA PARTS REQUIRED
 2 67-545 Pistons 9 to 1 compression ratio
 2 67-961 Inlet valves (oversize)
 2pr. Witham - Racing valve springs
 4 67- 1349 Alloy valve collars -
 4pr. 65- 1848 Alloy valve collars cotters
 1 67-357 Camshaft - Track & Road Racing
 1 67-358 Camshaft - Drag Racing
 2 RL47 - Spark Plugs

Note: when this was written the 650cc engine had a 70mm bore x 84mm stroke (up to 63).
But the later 650cc actually 654cc has a 75mm bore and a 74mm stroke.