If you already have a SRM Dynamo belt drive kit, and are upgrading your old dynamo to the Alton Alternator, our belt pulley will not fit the Alton alternator, so we have made a batch of small pulleys to fit the Alton units, so you do not have to replace your whole belt drive kit. Note still critical that the drive belt pulley housing is packed with grease to help lube the belt and pulleys and to keep them cool.