When using the Bantam engine in competition the need will sometimes be there to reduce the primary drive ratio. The most popular engine sprocket sizes are 12 and 14 teeth and can usually be obtained from your favoured spares supplier. To fit these of course requires the primary chain to be reduced in by 2 links and 1 link respectively. Even when fitting a new chain the amount of slack are above the makers recommendations. There fore the need for some type of tensioning will be desirable. The solution I have come up with is shown in the photographs below. This sturdy device will fit all types of engine as it locates on the two W fixings to the rear of the engine sprocket. Slots in the tensioner arm allow for setting the desired amount of adjustment to be set. On engine types Dl to D7 special fixings with threaded heads allow the outer cover to fit albeit using two shorter fixing screws.