Home • Know your Sunbeams • Sunbeamland • Running 'n' Riding • Workshop • Marston Sunbeam Register • Events






Kickstart segment
November 2008

Clive Larby from the UK contacted the web-site in August 2008. As the new owner of a 1929 347cc Model  1 or Model 2 side-valve machine he had a good deal of work ahead of him to get it back on the road.

This included the fabrication of the complete kickstart mechanism for a Sunbeam 'AT' wide-ratio gearbox. The required components were illustrated in an excerpt from the 1928 Marston's parts catalogue which was e-mailed (below). I had some sympathy, the segment itself has been in poor condition on every engine I've pulled apart - worn-down and missing teeth.

Some research from the Marston annual spare parts lists revealed that the parts were common to the 1928, '29, '30 and '31 side-valve models (and OHV models with the exception of Model 10).

Marston's parts' numbering system

Marston's lists in the late 1920s and into the '30s have two reference numbers for parts, seemingly a system introduced in 1927. In 1927 each part was given an 'order number' with a letter 'A' prefix. This was used for the purpose of ordering the part. Alphabet lettering was used for the following years, hence the 'C' designations in the diagram above denote parts from 1929 (although with no model changes, 'C' was also used for 1930).

The second reference number is a unique factory number for the particular part. This only changed when the design of the part changed. Hence the segment shown above as 'C.527' for 1929/30 is shown as 'D.782' for 1931. In both cases the factory-only parts reference number is '4517' - no change. In 1932 the segment has a factory-only parts reference number of '4157A', indicating a change to the design.

Photos of the missing parts

With that pearl of Marston knowledge, it seemed the parts on my own 1931 Lion would fit the 1929 Model 1 or 2. As a compromise between making full technical drawings and sending parts off as patterns, I was able to provide photographs against 10mm squared paper which with a few critical dimensions would hopefully assist fabrication of a set of parts. I advised as follows in an e-mail:-

"I have disassembled a kickstart from a 1931 Lion and have taken photos. I have photographed them against 10mm graph paper which may help you gauge some of the dimensions. You sent me diagrams with 'C' serial numbers (1929-30) so I assume that's the date of your bike. I have had a look at Sunbeam spare parts lists and the 'D' serial numbers for 1931 have the same 'factory use only' reference numbers for the parts you list. I hope the photos help.

"For info, the segment has a 2.5 inch radius, with fixed teeth over 140 degrees (loose tooth excluded). It takes the kickstart shaft which is 5/8 inch diameter and 8 - 1/4 inches long. The loose ratchet pinion is 2 - 5/16 inch diameter and has 20 teeth. Its width is 3/8 inch on the outer face. The central 'boss' on the inside face (onto which the spring fits) projects 7/32 inch. The central hole is 7/8 inch."

Note: the sprung tooth that slots into the segment is missing from the photos. Its purpose is to 'key' the teeth of the segment into the loose ratchet pinion on the clutch / drive shaft.

The resulting fabrication

On the basis of the photos and dimensions from the machine, new parts were able to be fabricated. These were made for Clive by Harold Beal - photos of his superb work in making sense of the limited information he had got for the precision manufacture of these parts speaks for itself.

The end result is shown in the photo below with kickstart segment and crank lever in place. Visible behind the clutch 'basket' is the sprung, loose ratchet pinion against which the segment engages. An excellent job!

Good luck to Clive in finding an outer half to the primary drive cover, piston, main bearings, fork springs and an exhaust pipe!



Clive contacted the web-site in July 2009 with an up-date on progress towards his target of participating in the Sunbeam MCC's 'Garden of England Run'. Read more ...


Return to: The Workshop