When Messerschmitt cars were sold new the manufacturer recommended that the petrol to oil ratio to use should be 25:1. The original phosphor bronze bush used with the aluminium conrod required such a ratio.
With most cars having had their engines rebuilt using a steel con rod and a needle roller small end bearing, the ‘correct’ oil ratio is now debatable, as this configuration has not been put through endurance testing to establish a revised petrol to oil ratio.
The lubrication required by the needle roller small end bearing is much less than for the phosphor bronze bush. An experienced member has reported that after using a 40:1mixture for 40000 miles with a steel conrod and needle roller small end bearing, he found no measurable wear on either the big end or small end bearings, or indeed on the main bearings. During this mileage the cheapest mineral two stroke oil was used. Continuing to use a 25:1 ratio will be completely safe.
