Engine numbers

It was an Experimental engine - "EXP" - design by the British during WWII as a countermeasure for the V2 rocket. It wasn't fast enough so was scrapped. No known survivors so yours is worth millions! ONLY JOKING - IT'S FRIDAY!

The "12" indicates a Model 7 500cc Dominator.

Cheers, Lionel

Hi Dominic,

The letter "P" could indicate the year 1959, even though the "20" is for an Atlas - which wasn't around until 1964 - so I think it was someone playing with their number stamps!

Cheers, Lionel

Actually the Atlas first appeared in 1962, not 1964. 1964 was the first year the Atlas was sold on the home market, prior to that it was only available in the USA.

Colin.

Previously wrote:

Hi Dominic,

The letter "P" could indicate the year 1959, even though the "20" is for an Atlas - which wasn't around until 1964 - so I think it was someone playing with their number stamps!

Cheers, Lionel

Doesn't the 'P' indicate Plumstead production ?

This is a right old mix of correct answers but several possible outcomes.

Much will depend on the positions of the numbers and letters to give a positive identification.

Early Twin Engine numbers up to the first model 88were usually bashed into the metal on the top left crankcaseabove the crankshaft end. Usually, but not always, there is a model number and the engine number. From around 1956 onwards, the engine number appeared under the camshaft tunnel bulge. About 6cm further back most (pre-1961) twins also had a model number and year identification letter stamped. If the letter P is stamped here then it means the engine is a 1959 build. If 122 or 14 or 15 are also in this area then the capacity and model type and hencesize of engine will be denoted by this.

If the letter P appears as a suffix immediately after the engine number then it usually denotes a Plumstead built item; post 1963. As Dominic states that his engine begins with 44*** this is too early for any 1963 twin engines which by then were being stamped 100000 plus. The number 12 by itself suggests a model 7; which would be 1949 to 1956 and engines numbers of 44*** were produced in 1952/3. generally with a letter G stamped near to the 12. So my money goes on a 1952/53 Model 7 for these crankcases.

For the other set 120060 is going to put this engine in the post 1966/67 group. My own Atlas was 120*** and registered 1967. It had a prefix number 20 and a P for Plumstead. The 88ss ended at 118*** but the 650SS was still around. The 650 engine would have 18SS stamped somewhere on the cases.

Final thought on these cases is to measure across the stud centres each side of the crankshaft line. Around 63mm would mean a small capacity 650cc or less engine. 66mm would put the motor in the bigger bore 750cc league unless it has been modified.