The Head
My BSA A10 head is the early Road
Rocket type commonly referred to as the Twin Carb Head, BSA casting #
67-1106. It has been fitted with hardened valve seats that will also accommodate
the RGS inlet valves. I use 1.5" racing inlets, which are SRM 215/1. The
valve collars are made from 2011 T6 alloy. Under the exhaust valve bottom
cup I use a Bakelite insulating washer from a Norton to help prevent excess
heat buildup damaging the exhaust valve springs. I would like to try Twin
carbs but on a ridged frame this is almost impossible. With the single
carb set up I am unable to use an air filter and had to shorten my manifold
by about 5mm. The frame casting above the carb has been ground away because
of the steeper angle that the carb sits on. My throttle cable runs down
the center of my top frame tube to operate my carburetor. The manifold
is fixed to the head with bolts instead of studs so it can be removed with
the carb as a unit if work needs to be done on it. While it's not easy
to fit an alloy head in a ridged frame, the extra performance gained is
Worth It!
A/ Inlet valve 1.5" racing SRM 215/1
B/Inlet alloy valve collar [2011 T6 alloy]
C/Exhaust alloy valve collar [2011 T6 alloy]
D/Exhaust valve SR 67-0967
E/Valve spring bottom cup SR 67-0886
F/Norton exhaust valve bottom cup, Bakelite insulator
The Rockerbox
Alloy head rockerboxs are different
from the cast iron head type. They are relieved to allow clearance for
the larger springs used on the alloy heads (see positions A). They are
identifiable by the manual stamping of the part # on the underside (see
B). I have lightened the rocker arms and polished them all over (see C).
Mushroom head tappet adjusters with alloy nuts have also been fitted (see
D). The rocker shaft springs have been replaced with solid washers to prevent
excessive end float at high RPM. A rocker breather has been fitted (see
Rocker Breathers page).
