BSA ENGINE AND FRAME MARKINGS

IDENTIFYING YOUR MACHINE.

First a word of caution to anybody buying a machine, particularly if it does not have any documentation or proof of origin. If you are not satisfied then do not buy as mistakes can prove expensive later. Remember buyer beware.

If documentation is available then check the details against the machine. On most BSA's the frame number is located in the following places, It is always stamped raised numbers are casting part numbers. Up until 1968 it is rare for the engine and frame number to be identical and where the frame is shared by several models the codes start with the smallest model e.g. all A series models have A7 or A50 prefixes with the exception of the Rocket Gold Star and Super Flash.

PRE WAR

On the front top frame member either by the front seat stay, by the steering head, or on the seat stem tube.

1950'S

On the front down tube below or in front of the petrol tank or on the headstock. The exception is the early Bantams where the frame number is between the front engine mounting plate. These are usually faint and small.

1960-65

By the steering head reinforcing plate or front down tube. Some Bantams on the engine mounting plate, these sometimes break and rewelding obliterates the stamping.

1965-1968

Usually on the front engine mounting lug.

1968 ONWARDS

Front engine mounting lug but the engine and frame numbers are the same.

1971 OIL IN FRAME MODELS

Steering head stem. The oil in frame B-series are stamped on the propstand bracket.

ENGINE MARKINGS

Engine numbers are easier to find usually by the crankcase mouth on the primary side. Exceptions are the Bantams which could be stamped on the front mounting point or just behind the crankcase mouth.

This is just a guide and will fit most situations but frames were legitimately restamped by dealers if the original was damaged and a replacement fitted. These could be stamped anywhere and often were not stamped at all!

IDENTIFYING ENGINE AND FRAME NUMBERS 1969 SEASON ONWARDS

Owners with late model BSA's can easily identify the month and year of their machine as the factory adopted a dating system for frame and engine numbers for the 1969 season models.

As with all previous BSA seasons the model year started after the factory shut-down in July so that 1969 models were those made between August 1968 through to July 1969. They would however have some machines in stock so that it is possible that a July model may be to either the previous or the next years specification.

The code consisted of three parts, the first as two letters giving month and year respectively, the second was a five digit number and the third a model code. The engine and frame received the same markings.

The date letters are as follows:-

To avoid confusion F.I.O. and L were not used, although it is easy to confuse C and G.

The numbering started at the beginning of each season and always started at 00100 leaving the first 99 for experimental use. The numbers were consecutively allocated throughout a model range so as an example all B group machines were lumped together irrespective of whether they were a B25 or B44.

The model designations are as follows. The years given are all model years:-

A SERIES

Note in 1972 the frames for the twins were marked A65 with no model designation, from XG.00101.A65 on.

B SERIES

This is a bit complicated!

D SERIES

OTHER POINTS TO REMEMBER

RIGID FRAMES

Early post war machines up to Z series had the frame stamped similar to the plunger or sprung frames e.g. YA7.R. 9999. Also this carried through to some but not all of the engines.

UNIT A-SERIES

1966 A series machines started the season with A50, A50B and A50C frame designations with the usual non-matching engine markings. After frame 3200 the engine and frame markings were the same. There was a short period where the engine marking matched the frame marking but the frame prefix was A50. Presumably to use up stock in store prior to the change over.

Machines still in stock in the 1967 season (about 1000) were resold in the 1969 and 1970 season. These returned machines are shown with a cross at the beginning of the despatch book record, they then reappear at the end of the book with the revised despatch date. The 1969 models are identified by the adding of an extra 0 at the end of the frame marking putting the number series into the 100,000’s.

Machines re-exported in 1970 were stamped with a Y suffix to indicate that they were 1970 models and therefore eligible for the increased warranty.

UNIT B SERIES

The C15 Sports Star 80’s and B40 Sports Star 90’s engine markings were often abbreviated to CSS and BSS respectively.

EXTRA LETTERS

A second series of letters and numbers starting ERS means that the unit has been replaced under the factory exchange replacement service and the figures are the despatch record number.

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©BSAOC 2000