John it looks to me as though the B4 chassis were stamped to match the frame. My chassis does not match, it has a higher number prefixed with an "S".
But this can't have been the case with pre war civvy chassis, as they were an optional fitting. I guess they started at No1 and just kept going for that model Chassis. The Civvy chassis that I had on my 16H was prefixed with an "X". Ron <
My Big4 chassis has two different numbers on it, one by the front fitting and the other on the spring platform as in Ron's pictures, I've never really been convinced with all the theories with the correlation of bike frame number, chassis frame number and then the little pressed plate in the body especially as some contracts had mixed quantities of passenger and box bodies?
Then there are the wartime RAF 16H combinations which may have had a W prefix number to match the bike?
As to pre and post war civilian sidecars there must have been a system with some sort of dating letter or sequence?
Yes it is ponderous Rob. My B4 chassis also has a different number in view on the front (5421) Why is there a different number hidden under the spring? Is the plate inside the box supposed to match the chassis? I think it's clear that it had a B prefix. When Lex got these plates made, I just asked for mine to match the chassis?? Ron
Yes, I did some research in the numbers, but nothing conclusive, SS cars certainly used the same plates on their Jaguar bodies, so it was an SS fitment, have pictures of 3 originals fitted to the Big 4 bodies.
There is no column in the factory ledgers for sidecar chassis numbers and they are shown neither in the case of the RAF Model G 16H outfits, nor the SWD Big 4.....It would seem that they were simply a 'shop' number that allowed them to be followed through the production process (which was probably on a piece-work basis so records needed to be kept of who made what)or to ensure that particular parts were mated up again after processes.
The BSA ledgers show tally numbers which I assume is what you mean by Shop numbers, so is that a possible theory for the second number on the chassis?
In the case of a military combination the sidecar body would presumably be the last thing to be fitted in the factory and would cover up the number on the spring hanger.
In the case of a civilian sidecar supplied by Norton in peacetime the majority would probably leave the factory to be fitted by a retailer so it would need a unique number for the guarantee?
Indeed Ron it's all really fascinating then hopefully I'll be able to pass it all onto them and they can pass it onto the next generation :) Hope you are all keeping well in these crazy times.