While five Mk2 chassis, complete with four-cam Ford V8s, qualified for the 1966 Indianapolis 500, the Weslake V12 was not available for the start of the Formula one season. The first Mk1s took to the track with old 2.7-liter Coventry Climax FPF inline-4 engines in their place. Once the Weslake was ready, however, the car proved to be highly competitive, if unreliable. The high-revving V12 had been constructed using surplus machine tools dating from World War I, so tolerances and parts interchangeability were poor. Nevertheless, when running the Weslake was an immediately arresting engine, with a distinctive V12-scream, and developed 360bhp even in its earliest development phase. By the end of the 1967 season this figure was over 400 bhp, easily competing with the Ferrari and Honda V12s, and the newly introduced Cosworth DFV V8. One mechanical flaw that limited the engine's power output involved a design mistake in the oil scavenging system. This problem—discovered too late in the development process to correct—caused oil to pool in the engine's sump, slightly reducing power. Gurney described the effect as "taking the edge" off the engine after three or four laps of a race. That year Beatrice Shilling was brought in to help solve the oil problem.