This blog, in addition to the usual maintenance details for classic mini cars, an attempt is made to explain the "whys" and "wherefores" of the various jobs.

Sunday, 18 October 2009

Engine and Transmission Lubrication

On conventional cars the engine oil has only to lubricate the engine itself. The gearbox and the final-drive gears in the rear axle have their own supplies of lubricant which, unlike the engine oil, are not subjected to extremes of heat, dilution by condensed fuel and contamination by carbon particles and by acid moisture. On the Minis, however, the engine, "gearbox" and final-drive gears share a common supply of oil, since all the gears and the differential are carried in the crankcase beneath the crankshaft.

It should not be necessary to emphasize, therefore, that "cheap" oils are likely to be the most expensive in the long run. Similarly, any temptation to delay oil changes beyond the recommended mileage is likely to result, sooner or later, in "expensive noises."

This is particularly important when an automatic transmission is fitted. Other types of automatic gearboxes normally call for the use of a special fluid but extensive tests have shown that normal engine oil can be used satisfactorily in the Mini automatic transmission provided that the oil is changed regularly at 3,000-mile intervals and that the oil filter is renewed at least at 6,000-mile intervals and more frequently if the warning light glows. After the specified mileage, changes begin to take place in the engine oil which alter the friction characteristics of the clutches and epicyclic brake bands in the transmission, upsetting the smooth operation of these units.

Owners of new Minis are sometimes worried by heavy oil consumption during the first few thousand miles. Oil may disappear at the rate of a pint in every 150 miles but experience has shown that after about 3,000 miles the piston rings should have bedded-in and the consumption should drop to a much more reasonable figure. By the time that about 5,000 miles have accumulated, for example, it should not exceed about 500 miles to the pint, although Mini-Cooper engines arc rather more thirsty if they are driven hard. Early Coopers, incidentally, gained a reputation for very heavy oil consumption but modifications which were incorporated in later versions reduced their appetite to a more acceptable figure.

Owing to the fact that the engine is not shielded by a warm radiator from the flow of air through the front grille, a good deal of sludge tends to form on the valve rocker gear and inside the rocker cover. This can be prevented by drilling two ,?, in. holes in the oil filler cap; but do not do this if a special crankcase ventilation system is fitted . It also helps to blank off the grille during the winter months.