BSA Exchange Replacement Service

BSA Provided an Exchange Replacement Service for all BSA Motorcyclists.
If you had eg. a worn out engine. You could get a repaired engine from the BSA factory.
You would have to give your old engine in exhange, for the rebuilt fully garantied engine.

The rebuilt engine would be marked with an ERS number, pressed into the engine below the engine number.

My BSA M21 Alternator model had the engine exhanged while doing service by the AA in England and has an ERS number.

BSA ERS number

Click on image to enlarge

All Information below was suppyed by>


In the 1960's BSA ran an Exchange Replacement Scheme. This page gives detailed extracts from the original leaflet, but please be aware that this is not a current scheme and this is purely for your information and interest. There is no longer any Exchange Replacement Scheme available, it is down to individuals like you and me to rebuild units to working standards.

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

Below is an extract from the above leaflets reproduced for clarity

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.


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