From the Dorman Records
The engine was despatched from the works on 23 June 1948 to E. Cleaves Esq.,Swanwick Shop, Swanwick, Herts. (adjacent serial 44111 was also despatched on the same day to the same gentleman)
The power output is not quoted but the 12hr marine rating would be 59 BHP at 1000 RPM, the max high idle is 1090RPM.
The engine is fitted with Fuel Pump BPE4B80Q310/3E
Idle speed 310 RPM.
Comment from the ex-Dorman engineer who looked at the records for us
I have made some enquiries about this engine and non of us has ever seen a bed plate design 4DLM, but as the engine resembles the prewar 4RB we concluded that it was a design from before the war based on the 4RB but with bed plate design and during the war updated to the DL pistons (same diameter) which gave better combustion.
When I was building 3 & 4 DL engines in the 50s the marine engine was a conventional industrial engine with marine additions.
While in the Record Office I found a document issued by Admiralty dated 1946 laying down specifications for marine engines and among the various clauses was one stating it must be possible to remove the pistons without removing the cylinder head hence the bed plate design.
To conclude this engine was in a batch of about 8 x 4DLM two went to Australia to Industrial Marine Power (Dorman agent) and the others went to UK customers. I therefore believe that the bed plate design was only designed for the Admirality. The Company was contracted during WW2 to Admirality so they would direct what was built.
Perhaps these engines are WW2 "left overs" certainly a rare one.