Take a closer look at the bottom section to see the cost of replacement units that were available to the public in the 1960's. All the prices are in Pounds, Shillings and Pence, as decimal currency did take effect until 1972.

Series 11	Series 12
Click on each of the above pictures in the tables to view the text

BSA. Exchange Replacement Units are built to a high standard and fully-guaranteed. They provide the most economical repair service available to motorcyclists.

To obtain the best results from your investment in an exchange unit always examine associated parts for wear or damage and replace if necessary. New BSA. control cables will add to your enjoyment of a service exchange engine or gearbox, whilst if you purchase a smaller unit such as a re-bored cylinder, there are specially packed BSA. gasket sets and engine repair kits to help you obtain the other parts essential to satisfactory completion of the job. BSA. service literature gives step-by-step instructions for carrying out repair work.

Ask your BSA. Dealer for any help you may require.

How the Exchange Replacement Service Operates.

The Exchange Replacement Service is designed to provide a rapid overhaul service on major components and assemblies for the owners of BSA. machines. Any of the replacement units listed in this leaflet can be obtained in the following manner:—

1. Ask your nearest BSA. Stockist or Dealer for the unit you require. If this is an item he does not carry in stock he will obtain it for you from BSA. Service Department. Care should be taken always to quote the fullest possible information concerning your machine, including the Engine and Frame Numbers with prefix letters, and colour of machine, if applicable.
   
2. When the unit is available your Dealer will ask you to bring your machine in and will retain it only for the period of time necessary to remove the old unit and to fit the replacement. If you intend to fit the unit yourself then your Dealer will require you to hand in the original at the time of collecting the replacement.
   
3. Your Dealer will then return the old unit to the factory for recovery. Normally this will be the end of the transaction as far as you are concerned, but you may be required to pay an additional sum if upon examination a major component of the old unit (such as crankshaft or crankcase in the case of an Engine) is found to be beyond repair.

 

The advantages of the Exchange Replacement Service are obvious. Your machine need only be off the road for a few hours while the factory-built replacement unit is exchanged for the old one and all exchange replacement units are fully covered by the BSA. Warranty.

For those who do not remember old currency.  
There was 20 shillings to £1 and 12 old pennies to 1 shilling.

Example: 7 - 17 - 6 is £7 - 17s - 6d (7 pounds, 17 shillings and 6 pence) or in today’s money £7 - 88p

The replacement engine and frame units were given ERS numbers, as can be seen on my engine.

 
Click on the thumbnail to expand.

Authors Note: 
            When I bought the C15, I checked the frame and engine numbers. At this point I noticed that on the engine case where the engine number was, there was also an 'ERS' number stamped on. I asked the BSA Owners Club about this, and they enlightened me to the fact that it stood for Exchange Replacement Service, and what that meant. Some months later at the Stoneleigh Show, I found a leaflet for £1 (series 12), which had all the information in it. Since then I was given a series 11 leaflet, and it is interesting to compare them. 

 This is what you could get in the 1960's, sadly, it is no longer available today.