The engine number

An engine number identifies a unit rather than a car. That distinction does most of the work here, because engines were exchanged over the counter by dealers in period and have been swapped by owners ever since. A car with a different engine is a normal old car, provided everyone knows.

Reading the number

The prefix places the engine in a family. The 3.8 litre engines carry an R prefix, and RA appears on engines built from early 1963. Series 1 4.2 litre engines carry a 7E prefix. A trailing digit records the compression ratio the engine was built with, most often 8 or 9, which is why two engines of the same capacity can carry visibly different numbers.

Read the stamping on the block itself. The plate in the engine bay repeats the number, and plates are easy to replace. On a car that has been apart, the stamping is the evidence and the plate is the summary.

What matching numbers means, and does not

• It means the engine currently fitted is the one the factory recorded against that chassis number.
• It does not mean the engine is original inside. A matching block can hold everything from original internals to a full rebuild with modern parts.
• It does not make an unmatched car a bad car. A correct type replacement, openly described, is ordinary sixty-year-old-car history.
• It does matter to originality, and it is the sort of claim that should be supported by a Heritage Certificate rather than by assertion.

When the number is hard to read

Stampings sit on a surface that has spent decades under oil, paint and heat, and a careless rebuild can leave them barely legible. Clean the area gently and read it in raking light before concluding anything. A number that cannot be read is a question. A number that has plainly been ground away or restamped is a different question, and one that needs answering before money changes hands.