BSA Motorcycles

Today in Motorcycle History

B.S.A.s for 1940...

B.S.A. 350 0.H.V. Silver Sports B 29

A broadside view of the 350 c.c. o.h.v. model B29. The castings enclosing the valves and the hairpin springs can just be seen below the tank. The new power unit utilizes a 500 c.c. crankcase and is a very robust, fast and flexible job.

BSA 1940 B29 Engine Diagram

The new 350 ohv power unit fitted with fully enclosed hairpin valve springs, which is employed in the model B.29. This engine is a most efficient job.

BSA 250 o.h.v. C11

The 250 c.c. o.h.v. model C11 is a handsome little mount. If has a good performance combined with real economy. The fork assembly has been improved for 1940.

BSA 250 o.h.v. C11 Engine 1940

A broken-open engine sketch Of the 250 c.c. o.h.v. engine fitted to the model C11. Observe the cast-in push-rod channels, the crossed rods, the simple timing gear, and the skew-gear drive operating the contact-breaker unit.

B.S.A. 350 S.V. C12 1940

The 350 c.c. B.S.A. sidevalve model C12. This machine is identical to the 250 side-valver except for the engine, which has a larger cylinder head and barrel, while the connecting rod and flywheel assemblies have been modified give a longer stroke. The gear ratios are also different, of course.

BSA 1940 250cc Fork Diagram

The new fork link assembly, giving greater rigidity on the 250 c.c. B.S.A. machines, is fully explained on the opposite page.

BSA 1000 S.V. Vee Twin G14

The only multi in 1940 range, the 1000 c.c. s.v. model G 14, which is ideal for heavy-duty sidecar work. It has a splendid reserve of power.

BSA 500 S.V. M20

The 500 c.c. side-valve model M20 B.S.A. which, except for engine capacity is similar to the 600 c.c. s.v. model M21.

BSA 500 O.H.V. Silver Star M23

The 500 c.c. o.h.v. Silver Star model M23. A popular machine, it boasts a fine performance, and is suitable for solo or sidecar work.

BSA 1940 QD Rear Wheel

B.S.A.'s quickly detachable rear wheel which can be slipped on, or off, in a few seconds. The rear extremity of the mudguard is also quickly detachable to facilitate +he easy removal of the wheel. As this photograph shows, a knock-out spindle and three studs are employed to hold the wheel in place.

BSA 1940 Timing Gear

This sketch clearly shows the very interesting and silent timing gear incorporated in several of the 1940 B.S.A.s. The cam pinions run on fixed posts which are pressed into the crankcase wall, whilst the steel plate shown carries an outrigger bearing for the main shaft.

A Range of Motorcycles designed to meet Wartime Transport Needs.

C 10 250 c.c. Side Valve

C 11 250 c.c. O.H.V.

C 12 350 c.c. Side Valve

B 29 350 c.c. O.H.V. Silver Sports

M20 500 c.c. Side Valve

M 21 600 c.c. Side Valve

M 23 500 c c. O.H.V. Silver Star

G 14 1,000 c c. Vee Twin

The C 12 and B 29 are entirely New Models for 1940


Five Side Valvers and New 350 o.h.v. Engine Dominate a Select but Comprehensive Range

IN spite of producing an enormous quantity of motorcycles for work of National importance, B.S.A. Cycles, Ltd., Small Heath, Birmingham, are offering a range of eight machines for sale to the general public. Every type of rider is catered for, but in keeping with the existing state of affairs, the inexpensive utility side-valve machine dominates the list, no fewer than five out of the eight models falling into this category. One - a three-fifty - is new from stem to stern, although it is based on the popular 250 c.c. s.v. C10. Further interest is aroused by a neat, well-laid-out 350 o.h.v. machine whose new engine is most up to date in every respect.

In the two-fifty class the C10 Side-valve and Cll o.h.v. machines remain as before, with the exception of one or two detail improvements. The pair of "three-fifties" mentioned make up the next class and are known as the C12 and the B29; the side valve being a utility job, whilst the new o.h.v. is a high-performance de-luxe mount. One side valve, the M20, and one o.h.v., the M23, fill the 500 class, whilst sidecar requirements are met with a 600 s.v., and the well-tried 1000 c.c. Vee twin - the M21 and the G14 respectively.

A new speedometer drive will be fitted to all models, except the G14, which will retain the straight-gear mechanism enclosed in the brake drum. The new drive is much neater and more accessible for greasing, being situated on the near side remote from the brake drum. A thin cable enhances the appearance, whilst it is claimed that the gearing is more trouble-free and less liable to suffer from the ingress of mud and moisture. An internal sleeve, running in a casing fitting tightly on the hub, has two pegs on it which mesh with corresponding slots in the hub itself. The outside of the sleeve forms the wheel part of a worm-and-wheel right-angled drive, the worm being connected to the cable. The whole thing is little larger than the hub and, therefore, very neat.

All eight machines have a standardized silver and chrome finish on the tanks, similar to that which was used on, the 1939 Silver Stars. The monogram is new to some models, being last year's Silver Star letters and circles the star removed, except in the case of the M23, which remains unaltered. Turning to the mechanical side, a totally enclosed positive-stop foot-gear change is used on the seven single-cylinder models, three speeds being fitted on the "C" range and four speeds on all others. The big twin still retains the gate change mounted On the off side of the tank and has the engine lubricated on. the total loss principle, in contrast to the dry-sump system which is common to the other seven.

Coil ignition, properly applied, is looked upon by many to be the most sensible and practical. type for the everyday rider, easy starting, weight saving and inexpensive maintenance being three "bull" points. Thus we find coils on the C10, 11 and 12, with a distributor, driven at half engine speed, incorporating an automatic advance mechanism. All other models arc equipped With a Lucas Magdyno, and, needless to say, automatic voltage control of the latest pattern is common to the whole range.

Where necessary, tyre sizes have been increased to give greater comfort and longer life, and in some cases the front-fork layout has been altered to give better all-round steering and handling. General equipment is up to the normal high standard and the finish is in keeping with the usual B. S„A. practice it can be seen that although prices have of necessity been increased to meet present-day conditions the value offered in the latest B.S.A. range is unusually good.

Starting with the lightweights, the C10 and Cll are real utility jobs intended for the man who cannot afford a big capital layout, but who wants a machine to give him unfailing service coupled with great economy.

Apart from the type of valve gear, the two machines are identical in design. Both have a bore and stroke of 63 mm and 80 mm., respectively, and are fitted with the coil ignition mentioned above. The coil is mounted under the tank, well out of harm's way, and a Lucas dynamo supplies the necessary current to the accumulator. In both cases a three-speed gearbox is used with an enclosed foot change, giving ratios of 6.6, 9.8 and 14.5 to l. Both front and rear wheels have had the tyre section increased from 3.00 ins. to 3.25 ins, the rims being 19 ins. diameter, and 5½ diameter brakes are used front and rear. A modification has been made to the fork link assembly which gives greater rigidity. One end of each shackle pin has a taper shoulder carrying one end of the link. The other end of link and pin is threaded to provide adjustment for side play. A right-hand thread is used in each case, so that the front and rear ends of each link assembly arc adjusted from opposite sides of the forks. This arrangement has been found more satisfactory than the old right-angled shouldered pins. The handlebar controls, etc., are identical except that the machine has a lever throttle control in place of a twist-grip.

Engine Details

Reverting to the engines, the side-valve job now has the cylinder head fins parallel instead of sloping downwards at the rear, thus giving an increased cooling area and a considerably improved appearance. It will be remembered that the valve gear is totally enclosed and pressure lubricated and an enclosed chain drives the dynamo. Altogether, a neat and serviceable little unit.

Last year the o.h.v. unit was new and fully described, but it would not amiss to recall a few of the interesting features. A detachable cylinder head is cast integral with the rocker housing and standards. The rockers are operated by crossed push-rods, an arrangement which enables the rocker gear to be simple and at the same time makes it possible to retain inclined valves. The push-rods are enclosed in a housing which is cast in one with the cylinder barrel, the rockers being enclosed by an aluminium cover. The whole gear is lubricated under pressure.

Both machines carry their petrol and oil in a divided tank, the capacities being two gallons of fuel and four pints of oil,

In the 350 c.c. class the side-valve model is the same in every respect as the 250 c.c. s.v., except that the cylinder barrel and the head are larger, the connecting rod and flywheel assemblies have been modified to give a longer stroke, and the gear ratios are altered to suit the increased engine size. The bore and stroke are mm, by 88 mm. and gear ratios 6.25, 9.2 and 13.6 to 1.

The new 350 c.c., o.h.v. is a thoroughly sound job with an engine which is based on a 500 c.c. crankcase and timing gear with a completely new overhead valve arrangement. The timing gear layout was introduced last year on certain models with a view to improved mechanical silence. The cam pinions run on fixed posts pressed into the crankcase wall and are positively located in, and supported by, a machined steel plate. This plate, being bolted directly on to the timing chest, is independent of the timing cover, and the latter is, therefore, in no way responsible for the alignment of the timing mechanism. The steel locating plate also carries an outrigger bearing for the main shaft, which helps to prevent any flexing of the shaft under load.

The o.h.v. 350

Oil is fed to the roller bearing big-end and the cam spindles through passages which are cast in the timing cover, an efficient seal between the spindle ends and the cover being made by means of small taper rubber washers. The tappets now have large flat with the valve clearance adjusters on them, and not on the push rods. crankcase is very stiff and adequate main-bearings carry the crank assembly. It is interesting to note that 1¼ ins. separate the drive side main bearings.

The cylinder head is detachable and cast integral with the rocker boxes which carry the rocker spindles. The valves are inclined at 75 degrees to each other and returned to their seats by double hairpin valve springs, the whole mechanism being totally enclosed by aluminium covers and lubricated under pressure. Tests have shown this engine to be a marked improvement, both as regards maximum power and general flexibility, over previous engines of the same capacity.

A four-speed gearbox is fitted, and the fork layout gives improved steering whilst it is hardly necessary to state that a cradle frame is used. A bore and stroke of 71 mm. and 85 mm. give 348 c.c., and the standard gear ratios are 5.6, 7.3, 11.1 and 15.9 to 1. In all other respects the general equipment is on the dc luxe scale, so that the new B29 is a good looking and most attractive proposition.

The remaining o.h.v. model is the 500 c.c. Silver Star, similar to the aforementioned B29 except for the overhead valve gear and the bore and stroke. The valves are returned by coil springs which are fully enclosed and positively lubricated and the engine is specially tuned to give a sports performance.

Source: Motor Cycling magazine, 1940.