Panther motorcycles were manufactured by Phelon and Moore for over 40 years and once the factory hit upon a sound design they tended to stick to it and successfully. Panthers are remembered for their reliability, their pulling power and their big sloping singles. They are also famous for their Red Panther light-weight models and the Stroud trials machines. This article will concentrate on the model that was the ultimate side-car machine of the time until it met it's demise as the result of an influx of Mini cars in the early sixties. Panther heavyweights had originally been developed in their OHV form in 1924. The first Panther was actually in the forefront of OHV design and set new standards for power, per formance and handling. The new Panther was designed by Granville Bradshaw, a respected aero engine designer who had also designed the luckless ABC. Bradshaw's design was notable for it's totally enclosed lubrication system which drew oil from a large sump cast into the front of the crankcases. This cast sump would become a hallmark of the Panther and was retained through all models. This motor was slowly developed and refined for the next 40 years, a period in which most British motorcycle factories changed hands or went bust, but Phelon and Moore stayed intact until the end. By 1960 Panther heavyweights had developed a reputation both for economy and reliability as well as for being a sidecar machine without parallel. The model 120 released In 1959 was designed to both tow a chair and to keep up with the heavyweight solo competition.
Historically, the Panther sloper heavyweight engine design had been perfected in the mid 1930's and the design had remained largely unaltered for 25 years, indicating what a good compromise Phelon and Moore had arrived at with this engine. The 650cc Sloper retained many of the Model 100 components, including the connecting rod and timing gears. The factory over-bored the Model 100 motor by 1mm and increased the stroke by 6mm thus providing the motor with heaps of low speed torque and a very satisfying rate of acceleration and a relaxing high cruising speed. The modifications made to the engine resulted in more power than the main bearings and crankcases of the Model 100 could cope with therefore the factory found it necessary to do some further redesign. The visible modifications included the replacement of the traditional U-shaped engine bolts which retained the barrel with 4 independent high tensile steel bolts and the main shaft was redesigned with a new keyed on parallel drive shaft and larger ball journal main bearings. A smaller exhaust valve, squish head and a larger Amal monobloc carburettor (389-33) combined with the other engine modifications to provide the Model 120 with 28bhp at 4500rpm compared to the Model 100's 24bhp developed at 5300rpm. The engine of the Model 120 was further differentiated from the Model 100 by the rather crude machining away of the 100 designation from the timing chest's winged motif, an action which left the previously attractive cover looking rather incomplete.
As the Model 120 was intended to be the definitive sidecar motorcycle it was only appropriate that the factory should also provide a purpose built sidecar chassis for the big Panther. Alwyn has been kind enough to allow the writer access to his model 120 for the purposes of this article. Alwyn's machine was originally fitted with a Canterbury sidecar chassis; however Alwyn has now taken the chassis off and sold the body whilst he tidies up the bike. The chassis and the chair body were very heavy items and were massively overengineered having 18 gauge tubing heavy enough to carry an elephant and its food. The sidecar was connected to the motorcycle by a three point mounting which provided minimal alignment problems.The sidecar wheel is interchangeable with the motorcycle wheels and has its own swinging arm suspension with an Armstrong shock absorber and side stand.
Alwyn's Model 120 was built in 1960 and was purchased by him in 1987, from a South Australian enthusiast, and came complete with the Canterbury Chassis, mentioned previously, and bearing a metal Tilbrook sidecar body. The handling of the outfit unfortunately was less than satisfactory and Alwyn soon found it necessary to remove the the chair to check frame alignment and fork action. The Panther required quite a bit of renovation as Alwyn discovered when he removed the chair and discovered that the front forks had very little movement and were practically seized.
When Alwyn unbolted the engine mountings the engine and frame sprang slightly indicating that the outfit had most likely collected something solid at some time shifting the alignment or bending the frame. Even so the "Heavyweight" tag of the big Panthers is well deserved for the bike is long and solidly built with massive frame tubing and castings, bulbous petrol tank and huge crank and barrel castings. The motorcycle practically shouts durability and strength and nothing has been built without some thought being given to its intended role.
The sloper engine dominates the motorcycle, however, it remains attractive due to its pleasing anglarity and polished alloy surfaces. The large triangular crankcase and the long and impressive 650cc barrel and head form an integral part of the frame, a design feature of the Panther since inception (and indeed on most P and M motorcycles since 1904 and on Joah Phelon's patented sloping motor first seen in the form of a Humber in 1901).
The long stroke of the motor (106mm) is evident from the sheer size and length of the barrel while the triangulation of the finned sump and timing chest is geometrically and visually pleasing. Theleft hand side of the engine is set off by a large polished alloy Primary chainclutch case. The Lucas magdyno is mounted above and behind the engine and is driven by timing gears on the right hand side of the motor. A useful item by the right footpeg is a toe operated lever which acts on the inlet valve cam follower. Use of this lever ensures that misfires won't occur when kick-starting. Earlier models without this lever could catch fire when the big piston back-fired during starting. Although the compression ratio is moderate at 6.5:1 the engine takes a mighty kick to start and well and truly exceeded my spindly electric-start spoiled legs. Standing on the kickstarter lever and grunting for all I was worth the kick-starter didn't even budge. Alwyn provided the necessary muscle and skill to get the motor turning over by easing the motor just past compression, retarding the ignition and then giving the lever one almighty, but confident kick. The motor started easily, certainly much more easily than Alwyn's Velocette. but I made sure Alvvyn was in sight at all times in case I needed to start the bike again. The big Panther settled down to a quiet idle with the exhaust note barely being audible over the clatter of the valve gear. Sitting on the Panther and grabbing the bars I was very aware that I was sitting on a rather large single cylinder motorcycle. Even at idle, strong vibrations could be felt through the narrow handle-bars. They were of a low frequency and very noticable.
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Murray Barnard, Perth, Western Australia
© 1996 mbarnard