Author Topic: Plunger gearbox Letters & Numbers  (Read 254 times)

Online WozzA

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Plunger gearbox Letters & Numbers
« on: 21.03. 2021 04:04 »
Today I called in to see old mate that sold me his dads '51 GF plunger,... for a coffee & a chat ...
Came away with a plunger gearbox & outer cover, a rocker cover & a stuffed inner timing cover.. for FREE  *smile*
The gearbox has a small capital letter L & numbers 20B stamped into it...     any ideas what the L stands for?
'51 Golden Flash Plunger
'57 Golden Flash Swingarm

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Online Superflash

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Re: Plunger gearbox Letters & Numbers
« Reply #1 on: 21.03. 2021 05:22 »
So the 51 plunger GF cost you a coffee and a chat??? SCORE.. all the new bits double SCORE..   *clap* . Suffice to say I have no idea what the markings are.  *conf*
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Online WozzA

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Re: Plunger gearbox Letters & Numbers
« Reply #2 on: 21.03. 2021 06:49 »
Guess I didn't word that too well did I..   Dohhh *eek*
Bike cost $1K   ... parts Free...  coffee & chat free... 
'51 Golden Flash Plunger
'57 Golden Flash Swingarm

Melbourne
The biggest lie I tell myself is
"I don't need to write that down, I'll remember it"

Online Greybeard

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Re: Plunger gearbox Letters & Numbers
« Reply #3 on: 21.03. 2021 09:12 »
So the 51 plunger GF cost you a coffee and a chat??? SCORE.. all the new bits double SCORE..
Damn, I was going to make the same comment 😜

Offline BSA_54A10

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Re: Plunger gearbox Letters & Numbers
« Reply #4 on: 22.03. 2021 02:21 »
They are production identification stamps.
If you ever decide to polish a set of cases you will find lots of them.
Parts were inspected using go / no go gauges and the gauge size got stamped into the part
Then there were batch numbers because BSA did not use modern "just in time" production planning.
Thus a gearbox casting could have been made anything up to 3 years before it was finally fitted to a bike.
So if for instance the 20 B was a gauge number , all of the 20 B's would go into a stillage till there was enough of them to warrant final assembly using the "B" set of shims on the "B" shafts .
Parts were mostly machined on production machinery using production workers.
The machines were phnumatically controlled so worked between stops.
The operator would take samples if it was a high volume production or check every one against a set of gauges.
They would either be tosses into stilages according to the finished size or when they got to a certain gauge the operator stopped the machine and pressed a bell alerting the tool setters to come & readjust the machine, change tools etc etc
There were no tradespeople fastidiously measuring then machining then measuring & machining as you or I would do today except in the competition shop , experimental shop rectification shop & other such departments .
BSA pioneered this method of production of motorcycles and cars starting back in 1926 with the round tank that was the first model designed to be built with fully unskilled ( well not trade qualified ) labour .
Th tradespeople made the tools and the gauges that the production workers used, not the actual motorcycles with the exception of the preproduction bikes including the trade bikes & some of the competition bikes .
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Re: Plunger gearbox Letters & Numbers
« Reply #5 on: 22.03. 2021 09:37 »
BSA_54A10
That was very interesting. My Grandpop, (my mother's father) was a capstan lathe operator in Chatham, (Royal Navy) dockyard. He was a farm boy before this. I imagine his job must have been along the same lines that you describe.

Online BritTwit

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Re: Plunger gearbox Letters & Numbers
« Reply #6 on: 23.03. 2021 23:57 »
Weather by design or chance, my three Super Flash gearboxes were stamped XX.

Offline BSA_54A10

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Re: Plunger gearbox Letters & Numbers
« Reply #7 on: 24.03. 2021 07:34 »
But where was the xx stamp ?
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Trevor