BSA Motorcycles 1950s

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!
BSA Head

BSA Head

BSA Head

BSA Head

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

BSA Head

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).

BSA Head


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