Sunbeam motorcycles began production in 1912, although the company had been in existence since 1859. John Marston, the owner, began by making pots and pans and from there went on to bicycles, motorcycles and cars. All of the items made by Sunbeam were known for excellent workmanship and the quality of the finish. The early machines were powered by either Sunbeams own single cylinder engines, or JAP V twins, and later models also appeared with Abingdon King Dick (I kid you not) V twins and Swiss built MAG twins. All through their history these original Sunbeams were campaigned in reliability trials and road racing, and were extremely successful.
In 1936 the company was sold to AJS. They had bought Matchless a few years before and the three companies together became known as Associated Motor Cycles, or AMC. In fact, AMC were hoping to get some new models with the Sunbeam acquisition, but were disappointed to find only a unit construction side valve. Furthermore, the designer, Dougal Marchant, laid claim to the design so AMC never even got to use that. The Sunbeam name languished for several years until a new range of 250, 350 and 500cc machines with huge timing chests holding high chain driven camshafts were produced. The new models had only been out a few months when World War II began and all AMC production went to machines for military use.
As the war ended Sunbeam changed hands yet again becoming part of Birmingham Small Arms, better known as BSA. Supposedly an advertising campaign was started in which motorcyclists were asked to write in with what they wanted to see in a motorcycle. From these parameters Erling Pope (earlier of Packman and Pope motorcycles but by then designing trucks) designed the ultimate refined machine.
The Sunbeam S7 of 1946 was an all alloy 487cc vertical twin whose cylinders were set one behind the other in line with the frame. It had overhead cams and shaft final drive. The first engines were rigidly mounted in the frame and the vibration was so bad that the first units had to be returned to the factory and the now familiar rubber engine mountings were added. The wheels were 16" with 4.75" section balloon tyres. A sports version with a more powerful engine was promised but never materialised as the bevel gear in the rear wheel was not up to handling any more power. The next model was released in 1949 and was called the De-Luxe, though basically all that changed was the colour from an all black livery to Mist Green. There were other minor changes such as the adoption of modern handlebar levers. In the same year the S8 was released, this machine was fitted with the BSA A10 (650cc twin) style forks and wheels which gave the bike a much slimmer, sportier look, though of course everything else on the bike was the same. Black was once more a colour option as was a new polychromatic dark grey.
The S7 and S8 soldiered on until 1956 when production ceased and the Sunbeam name was used on a rather sad little scooter.
Many thanks to Robert at Stewart Engineering for help with the work detailed below.
The Sunbeam pictured here arrived in a most unhappy condition, but all there. It wouldn't spark, and the kickstart didn't seem to turn the engine much before it would stick in the down position. The condenser had failed and an exact match could not be found, so a remote mounting inside the right side box was made and the condenser wired to the distributor points from there. On removing the side from the gearbox a VERY large amount of bronze swarf was found in the bottom of the box (see picture). A previous MECHANIC had rebuilt the kickstart mechanism with worn components and the thrust washer in the wrong place. Consequently the bronze worm gear wore away very rapidly (see picture).
Next thing found was a rather worn distributor cap. As a temporary measure the pickup on an old rotor arm was built up with solder and filed to shape. The bike now sparked strongly on both cylinders each kick, or more correctly, each push. Still no life so further investigations were made. The famous MECHANIC mentioned earlier had timed the engine on the wrong cylinder. Following the instructions in Stewart Engineering's invaluable bedside book that was soon put right. Tickle the carb, close the choke, and push gently and she started on the second attempt.
Engine and body parts were soda blasted and then the painting began. A two pack epoxy primer from PPG was applied and the black used was PPG DAR9000 which gives a nice glossy finish when mixed with a wet look hardener. The frame, forks and various other bits were painted and left to cure while the tank, mudguards and toolboxes were worked on. The worst dents in the tank were pulled out by a metalworker whom the owner had used previously and filled with lead. These and some minor dents and imperfections in the mudguards were then reshaped with a body filler, and finally skimmed with a two pack glazing putty. The same primer and paint were used but the parts were also given two coats of PPG urethane enamel clear coat. To take the very high gloss off and give a more original looking finish the paint was rubbed down with 1000 grit wet and dry and then polished.
To protect the paint while installing the engine the frame was wrapped in pieces of old innertube. The engine went in far more easily than it came out (why I don't know) and soon forks and mudguards were fitted and the pile of bits started to look something like a bike.
In order to fit the cast alloy airfilter cover a new mounting had to be made. The screw on filter backing plate for an Amal filter was reduced in diameter and then a bridge bronzed on in which was the tapped centre mounting for the cover. A suitable sized filter element was found at Tractor Supply and everything looked just as it did when it left the factory.
One of the most noticeable things on the very first model was the "clean design" handlebars and control levers. From photographs of originals supplied by Andy, another Sunbeam owner, I was able to convert a pair of Harley Davidson 1" bars into the Sunbeam type with the two exit tubes for the cables. We had a pair of the reverse levers which only needed some cable stops machining and fitting in their ends. The horn/dip switch and the throttle were another matter. From photographs and dimensions our ace machinist Hans made a perfect replica of the black ball electrical switch which works by twisting the left handlebar grip. Twist one way and you have high beam, the other and you have low. We were very fortunate with the throttle as we were given a replica that Andy had had made. As you will see from the picture it is complicated. The two brass inserts fit into the channel in the centre of a piece that slides into the suitably slotted handlebar and protrude into the spiral slots cut in the outer tube. When the twistgrip is turned they are forced along the channel, one side pulling the inner cable, the other side pushing the outer. Of course it didn't work as it should being very difficult to twist. This was traced to the cables being so tightly packed inside the handlebars that the outer could not be pushed. The lefthand brass slider was replaced with a fixed one so that only the inner cable was being pulled and voila, smooth throttle. The original clutch cable was used with a new nipple at the lever end, and a new front brake cable made.
So everything was completed and the bike was ready for a test ride. I started it each day while I waited for some decent weather. On the third day I noticed that the engine was getting a little temperamental about starting. Not only that, but each time I used the kickstart it didn't seem to turn the engine over much. then to my horror the lever stuck at the bottom of its travel, deja vu. I put the bike up on the bench and took the side plate off the gearbox, there was the dreaded bronze swarf. The kickstart quadrant had once more stripped off its teeth. This time a much more thorough inspection of the gearbox internals found the culprit. You remember the MECHANIC that I have mentioned. Well, when he rebuilt the gearbox he neglected to fit the circlip that holds the kickstart worm and ratchet in place on the shaft. On the first kick after rebuilding the kickstart mechanism the tension spring pushed the worm and ratchet along the shaft to the end, and the worm was completely out of line with the quadrant. Every kick took a little bronze off the teeth.
I was now faced with the prospect of having to remove the engine from the frame in order to get the gearbox off. As it turned out I needed to remove the rear wheel and drive in order to fill the gearcase with 140wt oil. Actually I needed to remove it because it had been packed with grease and the early models did not have a drain plug on the gearcase so the only way to empty it is to turn it upside down. I found that with the wheel out and the mudguard off, the gearbox and bell housing could be removed through the back of the frame. You simply disconnect the top and bottom engine mountings and jack the rear of the engine up to clear the frame cross member. With the gearbox out I fitted the circlip, new gaskets and oil seals. I also found that the clutch plate was soaked in oil so that was replaced with an exchange unit from Stewarts.
Everything was put back together, the engine turned over nicely and fired second kick. It trundles around beautifully and so far everything works perfectly.