 Like the petrol engines, the diesel was a Standard-built "20C" engine developed for the Ferguson tractor.The diesels fitted to the tractor were restricted to 2200 rpm and developed , but road-going engines in Vanguards had no limiter and so produced at 3800 rpm.However, they retained the tractor's "Ki-Gass", de-compressor and over-fuelling systems, all of which had to be manually operated when starting the engine from cold.