Part numbers & component introduction

[Paul Gasson]

Out of general interest can anyone offer any suggestions regarding factory changes to components and updates to the part number.

For example if an original first use part had suffix -54 when it was originally introduced, would that always be from the beginning of the manufacturing year on 1st September 1953? Alternatively, was it was from when the factory used up all the previously used assemblies. I can’t imagine there would be a hard cutoff from one year to the next but maybe there was.

When a modified or revised part was introduced, is it likely to have been across the whole range of bikes or was there a trickle down with the range toppers getting the change one year and lesser models a year or so later.

Just curious to find out how these changes were accomplished.

[simon.holyfield]

Interesting questions! I suspect Roger, as keeper of the works drawings, may be able to help.

[Roger Gwynn]

Depends! Usually a new part was fitted to the relevant models from the start of the new year. There are a few occasions when a part was changed during the year and they will usually not appear in the parts book until the following year and may have the suffix of the year they were listed, rather than introduced.

Parts sometimes changed without being given a new number, usually only if they were interchangeable but not always and today this matters to us but not then. For example there are 3 versions of the MKII exhaust manifold but they all fit all years and to the untrained eye they all appear to be the same.

Generally the new part would be fitted to all applicable models straight away, one exception is the change from girder forks to teles where there is clear evidence that the SQ4s had them before the 'lesser' models. There are also instances of last year's parts being used up on the current year and vice versa but this was nowhere near as widespread as people seem to think. I often hear that 'they built the bikes out whatever they had lying around', which is clearly ridiculous when the factory was building thousands of bikes a year. It does apply to the Meriden factory during the strike.

[nadab_sardar]

Thanks Roger, that's really useful, and it goes some way to killing the "built out of whatever was in the bins" myth. The bit about the parts book suffix being the year of listing rather than the year of introduction is a good one to know, as it would be easy to read a -54 and assume the part first appeared in 1954 when it may have been fitted a few months earlier.

The interchangeable manifolds with no number change also explains a lot. Makes you wonder how many "wrong" parts on bikes are actually perfectly correct for the period. Interesting that the SQ4 got the teles first too, I'd always assumed it was more of a gradual spread across the range.

[Roger Gwynn]

The suffix is usually applied in the year of introduction but occasionally it is a year later, sometimes never eg 5 versions of 4901-38 steering damper knob not all of which are technically interchangeable.