Edgar Franks - Norton Engineer

I was in a conversation with an old racer the other day about the development of Manx Nortons and the name Edgar Franks cropped up. I am sure many would have heard of Joe Craig who developed Norton’s Works racing machines, but the name Edgar Franks would be known by very few.

Edgar was a mechanical engineer at Norton who worked on many machines over the years. It was Edgar Franks who assisted Arthur Carroll and Joe Craig in the re-design of the Norton over-head-cam engine after Walter Moore left for NSU. Edgar also redesigned the Norton range for 1931. Changes he made included making new lower frames which made the rider adopt the knees fully bent riding position due to a saddle height of only 26.5”. Other changes included Norton making their own hubs, brakes and Webb-type forks, instead of buying in components.

In 1933 Franks designed the Norton model 50 350cc OHV motorcycle. It was also Edgar Franks that designed the Norton oil-bath primary chain case which was introduced in 1934 and used until the 1960’s. The first telescopic forks for a production Norton machine were designed by Edgar Franks for the 1940 Manx model. 

In January 1950 it was Edgar Franks who took Rex McCandless, the Featherbed frame and Rex’s jigs to Reynolds Tube Company. Reynolds went on to manufacture the Featherbed frames for the Manx Norton racing machines.

One of Edgar Franks’ biggest contributions was in the development of the Manx Norton production racing machines. For over two decades Franks continuously improved Manx to keep it competitive. It is a common mistake that Joe Craig developed the Manx machine – instead Joe Craig was in charge of the Works racers. So without Edgar Franks hundreds of racers would not have had such an effective racing weapon as the Manx Norton.

Charlie Bruce and the 250cc DOHC Velocette

This post is a brief introduction to the final Velocette racing motorcycle built by Charlie Bruce.

Charlie Bruce from Motherwell was a stalwart of the Scottish 250cc racing class. It was Charlie Bruce who go round the paddocks ensuring there was a good entry for the 250cc class throughout the 1950’s. Without Charlie’s passion for motorcycle racing, the 250cc racing class in Scotland would have probably ended.

Charlie Bruce at Beveridge Park

Charlie worked for the council in Motherwell, but had had tough times in WW2. He was at the ‘Death Railway’ (Burma Railway) and was a Prisoner of War. Charlie had some terrible treatment and it was only his dream of racing motorcycles that helped him survive his ordeal. During his time as a POW Charlie even produced the drawing of his racing machine using charcoal.

Charlie Bruce

Charlie Bruce was a very good rider winning the Scottish 250cc Championship in 1950 on his homebuilt bikes. Charlie was a Velocette enthusiast and until 1958 he rode an ex-WD pushrod Velo. There were various incarnations of this machine – I might go into these in another post at a later date.

Charlie was good friends of Joe Potts and much of the preparation work on his machines was done in Joe’s Bellshill workshop. Charlie became heavily involved with Joe’s own racing team, helping riders such as Bob McIntyre, Alastair King and Jimmy Buchan. Charlie was very well liked in paddocks across the UK and was well known by all the trade barons. It was because of this that Charlie became a bit like team manager for the Potts setup.

For 1958 the Potts team had been doing much work (see posts on the Desmo etc) developing new bikes. Joe made sure Charlie was not forgotten and talked with Bob McIntyre about getting Charlie a bike to replace his old pushrod Velocette. Bob organised the purchase of an ex-Works 250cc NSU Rennmax twin engine from Reg Armstrong for Charlie. Charlie kindly refused the NSU engine, saying he would rather finish second on a British bike than win on a German one! (he was an ex POW from WW2). It was back to the drawing board to find something for Charlie. Bob then located a 250cc DOHC Velocette engine that had been built by Doug Beasley. Bob paid Doug £257 for this engine.

This DOHC Velo engine was to be the basis of Charlie’s new machine. The engine had a bore and stroke of 68mm x 68.25 mm respectively. The crankcases, cylinder barrel and timing gears were all Mk8 Velocette KTT items. A special flywheel assembly was machined in order to reduce the engine stroke and the barrel was sleeved from the standard 74mm bore. An old Velocette factory racing cylinder head casting was machined and fitted with KTT valves which were reduced in size. The cambox was of Beasley’s own design and was clamped to the cylinder head by 16 ¼ inch BSF studs and nuts to faces machined on cylinder head. Standard Mk8 bevel gears took the drive from the crank to the cambox, but the flanged bronze bush which normally support the vertical bevel shaft were replaced by taper roller bearings. A 1¼ inch Amal GP carburettor was used with the engine. The engine produced 26.5 BHP at 8,500 RPM.  A should add here that this was the specification of the engine as first used in 1958. Over the coming years the engine had the Bellshill treatment and was modified heavily for extra performance.   

To house the engine a Razorblade frame (like the ones Bob was using for the 1958 season) was built by Alec Crummie. A Velocette 4 speed KTT gearbox and clutch was used. Shortened Manx Norton forks were fitted. A Manx 2LS front brake and Ariel/BSA type rear brake were laced into 19” rims. A Lyta aluminium petrol tank housed both the petrol and the engine oil in a section at the back of it.

I will add a follow post sometime giving some ideas what happened to the bike.

EMC Split Single engine

This post is detailing an engine which is a bit of a curio from the early 1950’s. The split single engine is a version of a two-stroke engine which uses two cylinders, but share only one combustion chamber.  The EMC split single engine here is based on some Puch components.

Joseph Ehrlich EMC 125cc split single development engine

In the split single intake charge enters the crankcase below the skirt of the front piston. The charge receives primary compression before passing through transport ports into the rear of the two cylinders. The charge travels up the rear cylinder and then transfer to the front cylinder via the bathtub shaped combustion chamber. The exhaust gases then leave the exhaust ports in the front cylinder. The front piston controls both the intake and exhaust ports, whilst the rear piston controls the transfer of charge from the crankcase to the rear cylinder.



Twin exhaust ports



Twin intake ports on side of engine

Asymmetrical port timing is achieved by pivoting the intake ‘slave’ connecting rod on the back of the main exhaust connecting rod. This allows the exhaust port to open before the transfer of fresh charge into the rear cylinder and also allow the transfer port to stay open whilst the exhaust port has closed.

A 'single cylinder' with two cylinders!

 

Combustion chamber

The benefit of the split single cycle comes with the separation of the intake and exhaust process. This allows much improved low speed and low load engine performance as well as reduced hydrocarbon emissions. Two-stroke technology in the early 1950’s was limited, as rotary valves and expansion chamber exhaust design was yet to be used widely. Instead conventional two-stroke technology often consisted of deflector type pistons to prevent intake charge leaving the exhaust port immediately.

It is clear that the split single has many issues which prevented it becoming widely used. The engine is larger and heavier due to the multiple pistons. High engine speeds are limited by the design and engine friction is higher than with a conventional two-stroke engine. The intake charge also has a tortuous path and combining this with a very large combustion area leads to poor efficiency.

The Anatomy of a 1954 Works Norton Featherbed frame

I thought I would make this post to give an idea of the difference between a Works Norton racing machine and its Manx production racing cousin.

We are only looking at the frame here for a 1954 500cc Works Norton. Striking differences can be seen immediately between it and a Manx Featherbed frame. The radius of the curve in the main tube as it goes from the top tube to the gusset plates on the works frame is smaller than on a Manx Featherbed.

Modifications to the rear mudguard loop carried out at the 1954 TT

500 stamped on drive-side gusset

It can be seen that the rear mudguard loop has been chopped off the frame pictured here. This was done in a hurry at the TT in 1954. An extra bracing tube was added between the top tubes at the same time. This frame is for a 500cc Works machine, as indicated by the stamping to the gusset on the drive side.

Pannier tank mounts and bowed drive side main tube can be seen

The drive side bottom tube is bowed out on the Works frame in order to clear the outside flywheel that was used on the 1954 machines. The timing side gusset and bottom tube are also relieved slightly in order to allow the fitment of a 5 speed Burman gearbox.

Oil cooler mount

The frame incorporates many Works specific features. On the top tubes there are mountings which hold the pannier tanks on either side of the machine. The timing side front down tube has a bracket added which supports the oil cooler which was used on the Works machines.



Front fairing mount



Weight saving inside the steering head

Front fairing mountings are also different from that of a standard Manx. The 1954 Works bikes sometimes utilised the rather unusual looking Proboscis fairing. The steering head on the Works frame is also undercut inside in order to save weight.



Rear chain oiler



The Works frame is made so that it holds lubrication oil for both the primary and final drive chain. The 1954 Works machine used a floating rear brake, with the brake-plate being unusually on the timing side of the machine. In order to facilitate this, the frame had to have a mounting for the brake torque arm on the timing side.

Rear brake mounting and modifications to clear the Burman 5 speed gearbox

As well as incorporating all the special Works extras not seen on a conventional Manx, the frame is of course much lighter than that on the production racing machine.

Ted Mellors Rotary Valve New Imperial

Ted Mellors was born In Chesterfield in 1907 and went on to become an extremely successful motorcycle racer – becoming 350cc European Champion in 1938.

This quick post concentrates on an unusual engine that was developed by Mellors in the early 1940’s. The base for the engine is a New Imperial single cylinder, but Mellors manufactured and patented his own rotary valve system for it. There was much interest in rotary valves engines prior to WW2, due to the potential benefits of higher compression ratios and mechanical simplicity over conventional poppet valve systems. Frank Aspin was probably the most well known exponent of rotary valves in the motorcycle field during the 1930’s.  

The Mellors rotary valve system utilised two conical rotary valves in the cylinder head; one for intake and one for exhaust. Unusually these rotary valves did not move continuously in sync with the crank, but instead moved in 90° steps. In order to achieve this more complex valve movement, a Maltese Cross mechanism was used. When the valves were in their stationary position a helical spring pressed them onto their housing so they were cooled. Just before the 90° movement of each valve, a face cam lifted each valve of its seat by a few thou. This allowed the valve to be rotated freely without excessive lubrication. The Maltese-Crosses themselves were driven by pins on the ‘cam’.

The Maltese-Cross system of valve operation would have been subjective to very high accelerations. Reliability at high speed and mechanical noise would surely have been major issues.

150cc Bruce Special New Imperial

The Bruce special was built by Charlie and his brother John of Motherwell. It was based around a 150cc New Imperial unit engine, to be eligible for the Scottish 150cc racing class. The full duplex swinging arm frame was a one-off built by Charlie Bruce with help from Joe Potts. Due to the lack of proprietary motorcycle rear suspension units, Charlie converted bomb door jacks that Joe had been manufactured in his engineering firm as part of the war effort and were also used on his 250cc  Velocette MAF.

The ‘Bruce Special’ was raced by John Bruce at various Scottish circuits during the early 1950’s, including Beveridge Park and Crail, as well as sand racing events. In 1952 the ‘Bruce Special’ carried the number 1 plate at the Beveridge Park road races. As the 150cc class was dropped in favour of a new 200cc Scottish class, the bike was converted to a 125cc and run in that event.

The ‘Bruce Special’ was sold by Charlie Bruce to William McBirnie, one of his friends in the Avon Valley motorcycle club. The bike was road registered in 1952, but William continued to enter races at Errol. The bike was then sold to another Avon Valley member, John Miller who used it on the road until 1958, the last time that it ran. In recent years this bike was located and purchased by Ian Whitehead & George Corner.

AJS Porcupine losing its spikes.

The 1951 AJS Porcupine.

During the winter of 1950, the AJS factory at Plumstead had been busy developing their 500cc Porcupine machine for the 1951 season.

The aim of the modifications was to produce “increased power, greater engine flexibility and an overall reduction in weight”.

The Porcupine without the spikes on the cylinder head.

Going to the engine, the most notable change to the Porcupine for 1951 is the losing of its spikes. For ease of development reasons, separate cylinder heads with horizontal transverse fins replaced the former cooling spines. This enabled detachable cam boxes and spring chambers to be incorporated, whilst the 14mm spark plugs are centrally located. The only other change to the engine is the enclosing of the main oil pump into the bottom of the crankcase to which is bolted a long boat-shaped light alloy sump holding over a gallon of lubricant.



New central floatchamber supports dual mixing chambers fitted with horizontal jets



An important modification was the use of a central float chamber. This enabled the carburettors to be mounted lower, giving a better sweep to the intake port. It was hoped that this modification would overcome the misfiring and uncertain running at low engine speeds.

The wheelbase was shortened by 1” for 1951 and weight was also shaved from the frame. Extra weight savings were made due to the absence if an oil tank and associated pipe work. The front forks were also shortened by 1” and a new alloy top yoke and two-piece sheet steel bottom yoke were used. Smaller wheels were fitted - 19 by 3.00 ins at the front, and 19 by 3.25 ins at the rear. The 10” front brake which was first used at the 1950 Belgian GP was refined slightly, but used for 1951. The rear brake remained unaltered.

New F.I.M. regulations meant than a new triangulated support for the longer rear mudguard was necessary. The seat was shorter than the 1950 design, and a zipped pocket was incorporated into it in order to hold two spare spark plugs.

The 1951 AJS Porcupine