An acquaintance asked me to post the photo of a marking on a early BSA M20 engine here on the forum. The stamping is on an early M20 engine which was found in Europe. Does anyone know what the meaning/purpose of this stamp is?
I have at least 1 early M20 engine with the same stamping myself.
I've got examples of at least 10 markings which I've only ever seen on BSA engines, and this is one of them. So I guess it's got something to do with early BSA quality control...?
I just checked and my WC10 has that marking also. Despite being a 1940 model, these were all despatched to the WO in Aug-Sept 1939 ( Also still fitted with the NiFe batteries) Ron
Unlike the JLO stamp (indicating a rebuild in the JLO factory in occupied Germany, see examples below), this can't be a WD marking, as Daryll found the same marking on every cam, flywheel, rocker box etc. of his 1920’s and 1930’s BSAs. And I've never seen this zigzag marking on a Matchless / Enfield / Triumph / Norton / Ariel...
That's all pretty convincing ! I wonder if individual quality contollers at BSA had their own stamps, similar to how the later ministry inspectors had a unique number. It would explain why the symbol doesn't appear on all engines or parts and that there are apparently others too.
I'm sure there were also other BSA quality inspector's markings. See examples below. I've never seen any of these on another make.
First example: number 51:
Second example: BSA F5:
Third example: B on a hammer:
Plus some combinations:
Message to the forum members: please have a look at your engines, and please share what you found. Either by adding the pictures to this thread, or you can also send them to me by email (address below).
Back when these bikes were made most of the tooling was plain high carbon steel which goes dull fairly quickly
From the days of the Round Tank BSa used production line workers to do the machining of parts rather than fitters or machinists.
The machines were production line machines which worked between fixed stops so as a tool wore there was no way of compensating on the fly.
The operator would have a series of go / no-go testing gauges and they would check each & every part as it came off the machine
Most times it would then go into a stillage according to which gauge it fitted.
The stillages then went to a QC inspection station where better gauges were used to grade all of the parts and each grade would get a stamp so at a latter date say an oversized bushing hole could be matched up with an oversized bush.
When a certain threshold of out of spec parts came off a machine, the operator hits the OFF button and calls for the machine fitter / tool setter to come over and correct the machine .
The cycle continues at infinatium till the run of that part finished.
THus the original engines were sort of blueprinted to achieve the best overall fit .
So if you look hard you will see a massive amount of stamp marks all over the engine, many of them so small you need a strong magnifier to identify them .
Then here wer other numbers like those on the front engine mount that signify that those 2 parts were machined together so when reassembled they have to go back together so the crank shaft is perpendicular to the bore
Where I see this variation most often is with the magneto plaatform
Originally they were machined together so were flat
When you replace a left or right case half often there would be a step on the platform.
Commonly referred to as 'selective assembly' and used widely and routinely in the days before CNC machining tolerances and consistency...For a 'modern' engine that employs the system to a degree you need look no further than an early to mid 2000s Harley Davidson Sportster....There may be others...
It's worth considering when rebuilding your old army machine with say, a nos set of timing gears bought from different suppliers that the tolerances might not be correct and will still require careful checking (ask me how I know)...Theoretically, at least, you ideally need a full set of 'matched' gears...Ian
It's a lottery really...Without knowing how many tolerance classifications there were, how close the tolerances would be and how many spares there are for any given part it's impossible to calculate the odds of achieving a match...
I've used 'full sets' of mix and match gears a number of times and achieved mixed results...I've had good sets and some where the gear tooth clearance was insufficient...Ian
This is partly why I've put a new set of gears, shafts and forks in my gearbox. Even then it's taken some selective fitting to get things in the correct places.
One sin often committed is to run a new gear with a worn one.
Oh, what fun we have.