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Difference between revisions of "BSA A7"
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The construction concept can be found on Scott engines using a normal clamp bolt while the differential screw is used in Hirth crankshafts which are built up from individual components locked together with radial teeth. This complex and expensive design was dropped in favour of convention by the time units reached the public. The rocker boxes were separate alloy castings each retained by five fastenings. Each pair of rockers ran directly, without bushes, on a long spindle across the box which was supported by an internal rib in the centre and secured by a dome cap nut on the right-hand side. Early models relied on oil mist lubrication but from early 1948 the shafts were drilled to take a positive oil feed taken off the oil return pipe. | The construction concept can be found on Scott engines using a normal clamp bolt while the differential screw is used in Hirth crankshafts which are built up from individual components locked together with radial teeth. This complex and expensive design was dropped in favour of convention by the time units reached the public. The rocker boxes were separate alloy castings each retained by five fastenings. Each pair of rockers ran directly, without bushes, on a long spindle across the box which was supported by an internal rib in the centre and secured by a dome cap nut on the right-hand side. Early models relied on oil mist lubrication but from early 1948 the shafts were drilled to take a positive oil feed taken off the oil return pipe. | ||
This form of rocker cover design was arrived at after many different arrangements had been investigated. One such design was for a one piece cover over the whole of the valve gear. Accessibility would have been great and would have dispensed with the pushrod comb, so beloved amongst A7/A10 owners, however the problem of keeping such a cover oil tight was beyond the 1940's technology. Fifty years later such covers are common with OHC engines which have a much more copious supply of oil. The cylinder head was formed as one casting with a separate manifold bolted to it, to which the | This form of rocker cover design was arrived at after many different arrangements had been investigated. One such design was for a one piece cover over the whole of the valve gear. Accessibility would have been great and would have dispensed with the pushrod comb, so beloved amongst A7/A10 owners, however the problem of keeping such a cover oil tight was beyond the 1940's technology. Fifty years later such covers are common with OHC engines which have a much more copious supply of oil. The cylinder head was formed as one casting with a separate manifold bolted to it, to which the carburetor was bolted. Originally there was no drip tray but after several fires this essential piece was designed to take the petrol drips away from the sparking magneto. The cast iron cylinder barrels were deeply recessed into the crankcase mouth with the pushrod tunnel cast in and the head attached to it by nine bolts with a copper and asbestos cylinder head gasket fitted between the two. | ||
The crankcase was along traditional lines being split vertically on the centre line of the engine. The left half being extended back to form the inner section of the primary drive case whilst carrying the ball races which located the crankshaft. The right case was smaller with a small rearward piece to carry the magneto and two semi circular supports for the dynamo. The timing side bearing was steel with a white metal facing. Combined the bearings gave the bottom end a life expectancy in excess of 30,000 miles provided the oil was changed frequently. | The crankcase was along traditional lines being split vertically on the centre line of the engine. The left half being extended back to form the inner section of the primary drive case whilst carrying the ball races which located the crankshaft. The right case was smaller with a small rearward piece to carry the magneto and two semi circular supports for the dynamo. The timing side bearing was steel with a white metal facing. Combined the bearings gave the bottom end a life expectancy in excess of 30,000 miles provided the oil was changed frequently. | ||