Tuesday 26 March 2024

The Rolling Chassis ….and a Day at Brooklands

Regular readers of my blog may have noticed that there is a one-month gap between my previous posting and this contribution. There is a good reason for this: building/rebuilding/restoring 3 motorcycles simultaneous is turning out to be my self-imposed Labours of Heracles. I decided to do the builds this way because there are efficiencies for repetitive tasks, for example, when setting up machining operations, nevertheless the elapsed time is still pretty close to 3x the time it would take to do one.

As I mentioned in a blog some time ago, one of the first objectives is to get the rolling chassis – frame/forks/wheels/tyres to a state where they can be moved around. My total workshop floor area is 30 m2 and I simply do not have sufficient space to build 3 bikes simultaneously.

The wheels came back from my wheel builder immediately after Christmas – when I was in the middle of making cambox oil pumps and, in the meantime, I had ordered tyres & tubes.

These are Avon Speedmasters for the front and Ensign Universals for the rear – all 3.00” x 21”.

The observant will notice that there are only 5 tyres ….for 3 bikes. I believe that I have exhausted the supply of these particular Ensign tyres here in the UK as I cannot find anymore anywhere online. They are made somewhere in the Far East and so the next incoming batch is probably stuck on a container ship that is now sailing around the Cape of Good Hope to avoid missile attacks if they take the shorter Suez Canal route. Luckily, I have just found a barely used Ensign tyre of the correct size in my garage so I won’t be held up.

After checking the offsets of the newly-built wheels (making sure that they are exactly in the correct position with respect to the frame/forks) and putting on the 5 new tyres (not my favourite job!). I now have 2 ½ rolling chassis.

Apologies for the clutter in the above picture; KTT 305 is on the hydraulic bench (in primer), the cammy special is on the floor beneath KTT 305 with the front wheel in the forks (which have not yet been attached to the bike) and the rear wheel awaiting tyre fitment and KTT 55 is in the foreground on the table.

The crankcases in the above pictures are spares – they belonged to the engines that donated their cylinder barrels/heads/camboxes to the AJcette and V-Twin projects are have been added to give structural strength to the chassis during the dry build.

A couple of final things are needed before I can easily move the bikes around: handlebars and handlebar clamps.


Handlebar Clamps

A few weeks ago, I posted a picture of numerous castings that had just come back from the foundry - see here. All of the girder fork links and brake levers shown in the picture on this link had already been machined and fitted (the rockers are for a bronze-head Ariel owned by a buddy of mine) and it was now time to start machining the handlebar clamps, shown below with some originals on the right of the picture.

This turned out to be over one week’s work; for 3 bikes, there are 3 x 4 clamp tops and bottoms in total, which require, for each clamp pair, 8x holes – 4 clearance and 4 threaded (5/16” BSF) for the clamp bolts plus the 2x larger holes (7/8” for the handlebars and ¾” to clamp to the girder fork top yoke). There are also 24x 5/16” high tensile BSF bolts required.

The first step in machining was to face off the top and bottom surfaces.

Pairs of castings were then taken in turn and clamped together

before setting up in the milling machine to drill and tap the centre holes.

The 20mm x 3mm aluminium strip that is sandwiched between the clamps - and will be discarded when machining is finished, is to ensure that the larger diameter holes fit properly to the surfaces of the handlebars and forks when fitted to the bike.

The first 2 holes could then be used to clamp the upper and lower parts together

before drilling and tapping the outer holes.

After a few days the first major part of the machining is completed.

As I mentioned previously, the material is AB2 Ni-Al bronze and machining this, particularly drilling, can produce a lot of heat and I have used solid carbide drills for removing the bulk of the material.

The second stage is to machine the 2 larger holes for the handlebars and forks. To accurately position these, pilot holes of 5/8” are drilled on the milling machine

before setting up each hole in turn in the 4-jaw chuck on the lathe to bore the holes to size. To help in the positioning in the chuck, a 5/8” on-centre milling cutter is inserted into the hole before carefully tightening the chuck jaws

and with final adjustments using a dial gauge.

The holes are bored to size using a small boring bar rather than drilling because this puts considerably less load on the part and avoids the clamp shifting in the chuck.

The clamps for all 3 bikes are now finished

and I can turn my attention to the handlebars.



I used to buy excellent quality handlebars suitable for girder fork bikes from Scottparts; these are fitted to, for example, the V-Twin. Unfortunately, the guy that used to supply these retired and I haven’t found anywhere that can provide suitable replacements.

According to the Spares Parts List the part number for the handlebars is FK-61. The Velo Owners Club can provide FK-61/3 (which are for MOV/MAC/GTP Webb Forks) and I ordered 3 of these. They are beautifully made but cannot be used directly because the central straight section is too short to be fitted to the clamps and I therefore decided to chop them in 2 and add a section in the centre. The picture below shows both chopped and unchopped bars and a length of 7/8” diameter stainless steel to be machined for the additional section.

The central section was extended by 3.25” and with 1.125” spigots at both ends that are a good interference fit into the 2 half bars.

After silver soldering the new section in place and polishing

I now have bars that fit correctly to the new clamps.

The bars will be trimmed back to reduce the width at some stage – when the controls are fitted, but for the moment, I can at least move the bikes around easily.

All the handlebars are now made in stainless steel and these will be chemically blacked in due course to avoid them looking too “blingy”.

In the meantime, the next job awaits…

A Day at Brooklands

Last, but by no means least, it’s good to get out of the workshop once in a while and the SunbeamMotorcycle Club recently celebrated it’s 100th Birthday at Brooklands. For those that are not conversant with UK motor racing history, Brooklands was the first banked motor racing circuit in Great Britain and was built in 1907 – see Wikipedia entry here.

I took the AJS V-Twin along to participate in the finishing straight parade. The original bike does have in-period Brooklands history - see pictures below taken in 1930

Acknowledgements to Steven Mills from whose book “AJS of Wolverhampton” these pictures were taken and to Geoffery St. John for the originals.

but I did not attempt to try and recreate these atmospheric pictures with my replica. The day was thoroughly enjoyable and provided the opportunity to meet up with a few hundred like-minded people that like old, noisy, smoky motorbikes.

One of the most interesting bikes there was brought along by Ian Hatton. Ian is the proprietor of Verralls, the vintage, veteran and classic motorcycle dealer in Handcross, Mid Sussex. I have known Ian for many years and I have both bought and sold bikes through his establishment - he is also more knowledgeable about these ancient pieces of machinery than anyone else that I know.

One bike that he acquired some years ago has an engine with a rotary valve in the cylinder head to replace the usual inlet and exhaust poppet valves. In the early days of 4-stroke reciprocating engines and before poppet valves became the established engineering solution for getting fuel and air into the cylinder and the exhaust gasses out, alternatives, many of which involved some kind of rotary valve, were proposed. A couple of the more well-known ones (in the UK) are the Aspin and Cross rotary valves but there are many more; eventually all of these fell by the wayside and I do not know any that have ended up in production engines and stood the test of time. Just to be clear, I am not talking about rotary engines, such as the Wankel, or disc valves in 2-strokes.

Anyway, back to Brooklands. Ian brought along a bike that has a running rotary valve engine. The valve rotates about an axis aligned with the centreline of the cylinder and is driven by a skew gear which, in turn, is chain driven. The engine is built on De Dion crankcases and has a magnificent petrol tank that is also a radiator for the water-cooled cylinder head! A brief video that I took of the bike running and out on the track is below.

A great day. Thank You to Julie Diplock at the Sunbeam MCC for organizing the event and to Brooklands.