The WLB9 was a straight continuation from the WLB8 range taking off where the engine numbers for the WLB8 finished. It is not known exactly when the WLB9 range was introduced but it can be assumed that production ceased around 1972 with the total number of WLB8/9 engines produced totalling over 46,000. With the WLB9 came the introduction of another style of smooth hopper and the use of a flat, Lister style exhaust and the Lucas SR magneto. It can be assumed that the use of the flat exhaust was a cost reducing measure. The use of the Lucas magneto can be put down to the fact it was a newer design than the older Wico A series which had been around for some time at this point. Tank cooling was available as an option as was petrol or petrol/paraffin models. The WLB9 engines are generally found to have been supplied as twin flywheel engines due to the larger power outputs, it is not known whether a single flywheel model was produced.