Found this interview with John Nelson here

It details how the build process worked at Meriden, no doubt a similar regime operated at Small Heath with some changes.

Between March 1957 and 1973 Triumph at Meriden produced some 75,000 ‘C’ range machines along with the numerous other Machines in the Triumph range. I have been fortunate to interview John Nelson who wrote the following article.

I am always amazed by the vast range of questions that are asked regarding the production of motorcycles from the original factory in Meriden. Most can only be answered from the ‘incomplete’ records made at the time, and the memories of the dwindling few that worked there, and still exist (and retain their memories)!
My first statement is that there was no one at the factory who was detailed to study and record each individual machine and function so that he could recall precisely sixty years later. What records that were kept were for business and legal purposes.
Secondly, Triumph was not just a motorcycle assembly shop from bought in finished components as were many other makes. When I joined in nineteen fifty, they made their own pistons, frames, gears, shafts, clutches, wheel hubs-polished and plated their wheel rims, handlebars, silencers in modern paint, polishing and plating shops. The machine shops manufactured almost every part for engines and gearboxes, and all was subject to very strict inspection and quality procedures.

So! How did it all work? In the nineteen fifties and sixties, Edward Turner was in charge. Each year he approved design changes, and new models down to every nut and bolt. Most proposed changes were submitted by Sales for acceptance following market trends and Distributor and Dealer requests. Once agreed, the new seasons models were specified by the Design Department, and a specification issued for each model, by part number detailing quantity, material, etc. indicating ‘new’ where appropriate. When these were issued, Sales issued a programme of forthcoming sales requirements which went to the Purchase and Production departments. Purchase had to schedule deliveries of raw materials to cover manufacturing requirements in time for Production to commence at the proposed date. Tallies were issued to each section in the factory detailing quantities for each individual component in scheduled batches for delivery in time for inspection, and transfer to the central ‘finished ‘ stores. The finished stores was in a central position in the assembly area, midway between the engine and gearbox assembly tracks, and the motorcycle final assembly line.

By this time, the Sales departments (Home and Export) had collected the forward orders for the forthcoming season, and converted these into coloured cardboard Tallies (White for Home and General Export, and Pink for Overseas Markets), detailing individual model, destination, Distributor or Dealer, additions to specification, packing and despatch etc. All these Tallies were collected in single model and destination batches and passed down to Production and Planning to be attached to the bare assembled frames, forks and wheels and handlebars, as the machine was placed on the final assembly track. By this time the Engine Assembly track, on the other side of the finished stores, was commencing build of the new seasons specification engines. Nothing had a frame or engine number at this point. As the engine ‘grew’, and after the pistons and barrels had been fitted, the designated operator sequentially stamped each individual letter and number on the crankcase, whilst standing by the engine at waist height, (not easy!) and then recorded it in the build book. Passed on to the next operators, the engine was then completed, collected in a batch at the end of the track, and then shipped in batches round to the final assembly track, and fitted into the next frame going down the line. The engines were picked from the engine bench supply in random order and it was not until the last operation on the finished motorcycle, just before it was passed down to the testers that the frame number (taken from the engine number) was stamped by hand, using individual stamps on the headlug -(later an adhesive label), and the number entered on the Tally, and then into the build register. On rare occasions, due to frame hold-ups, large stocks of engines gathered awaiting build, and no attempt was made to ensure they were segregated and then fitted in chronological order. An engine was a bike; which was an invoice, and an income.

When passed test, (or rectification, and then re-test) the machines were delivered to the Despatch department, stripped as required for shipment, packed, crated - or delivered by truck, as specified. A dispatch record of every machine was also logged by the despatch department, the completed Tallies were then returned to the Sales departments, and the final records completed….and the invoices dispatched. During every stage of the above procedures, there were a large complement of progress chasers, based in the production department whose sole job was to ensure the material from the ‘rough stores’ was presented to the various machining sections in time for each batch manufacture, heat treatment, plating/polishing in accordance with the schedule, and available in time in the central stores for each day’s supply to the tracks in accordance with the day’s model build programme, (and as you will appreciate, the constant supply of finished material for the Spares Department).. Everyone knew the programme, and what they were building, normally starting with 650 6T’s TR6, T110, and T120, in those days, and eventually 750’s TR7 and T140’s. In the early days 350/500’s and Police and military were usually at the end of the sequence. Then it was all round again and no going back to earlier models.

New models were usually introduced immediately following the Annual Works Holiday, when a skeleton staff had been retained to install the new jigs and fixtures to be used for subsequent production, and a number of dummy runs made to solidify any new installation procedures required for the return and start-up when the operators returned- so all was ready to go! This was the time when the routine changed to supply the U.S. with early consignments of the new models, so they could be shipped and distributed and displayed across the USA in time for the spring selling season. Imagine what happened when the new frame from Umberslade was introduced three months late, and then the engine couldn’t be installed. The entire selling season was lost, and the decline set in.