The Vokes Oil Filter was an optional extra. It was mounted behind the RH cylinder on a steel pate that fitted on the upper and middle barrel studs. The awkward bit is drilling the front crankcase half for an extra pipe fitting so that the oil can be rerouted through external oil pipes via the filter before returning to the original vertical drilling that goes up to the front main bearing. Also, to complete the conversion, a blank has to be inserted in the original oil gallery to prevent oil bypassing the filter.
Unless you already have one of these filters, it is unlikely that you will find one - they were not very common! When we were involved with the LDMCC spares, we contacted Vokes in the hope they may be able to supply some filter elements - they eventually rang back to say they couldn't find any reference to their filters on a Douglas!
Regards,
Eddie.
