These were incredibly reliable cars and they covered enormous mileages with few problems, however R-R did make two serious mistakes.
They had discovered that if the top 2” of cylinder bores were chromed, it virtually eliminated bore wear in aeroplane engines. Sadly, because aeroplane engines are not used to “nip round the pub for a packet of fags” no one knew that it wouldn’t work on MKVI engines and that if re-chroming was necessary, it meant totally dismantling the engine. So they did something even less sensible. The pressed a 2.5” long liner into each cylinder bore. It was made of a harder material than the cylinder block and although it did not wear, the bore below did. This eventually caused disintegration of piston rings and lands, especially if the cars were driven over about 60 mph on motorways. As has already been stated, many of these cars have not been re-bored or re-sleeved and yet have completed several hundred thousand miles. This is because they have been treated fairly gently, however if their engines were stripped down, the pistons would be in a state, and if it were driven at high speed up the motorway, they would certainly break up. An increasing number of cars now have full length sleeves in them, having had engine rebuilds and these are the ones to go for if you are looking for a car.
All 4.25L MKVIs, Silver Wraiths and Dawns were fitted with a By-pass oil filter. At the time engineers had trouble filtering out sufficiently small particulate matter with full flow filter (where all the oil rather than a part of it went the through the filter on its way to vital bits in the engine) without it clogging and reducing oil flow to the engine. By-Pass filter, in theory, kept the oil cleaner. In practice, it was impossible to get rid of all the sand from the block casting process or to clean out the swarfe caused by machining it. The big ends survived because the hollow galleries of the journals acted as centrifugal oil traps but the main bearings failed after a relatively short time. R-R converted most cars that they or their agents rebuilt but surprisingly there are still cars around with low oil pressure and a by-pass filter. It was a very strong engine and could survive for years in a very worn state.
The above description applies to cars that are in perfect working order but very few actually are. Through the pages of this website it is our intention to give sufficient information to enable owners to restore their cars to original condition and where possible, using later knowledge, to actually improve on their original performance.