Help me!What is this?

[laverdina]

Sturmey-Archer engine No.-DPRO CE203

[Justin_Faithfull]

Raleigh used to make engines for motor cycles. The ones they fitted in their own machines were badged as Raleigh engines & the engines they made  for other motor cycle manufacturers to use were badged as Sturmey Archer (Raleigh owned Sturmey Archer).
I do not know how many different companies Raleigh sold their Sturmey Archer engines to.
What make is the gear box? The hubs look rather later than the rest of the bike. Also are there any numbers stamped on the frame anywhere?

[laverdina]

I havent found any number on frames , and gaerbox is sturmey archer

[33d6]

Dunelt were a major user of Sturmey Archer engines in the late 20's early 30's. I suspect you may have a Dunelt.

[33d6]

I knew I had some info on Sturmey Archer engines somewhere and it has taken me a while to put my hands on it.
Each letter tells a story and identifies what manufacturer the engine was made for.
Your engine number is DPRO CE203.
The code is as follows,
First letter, identifies engine type & capacity. D = 496cc, b&s 79x101(inside flywheel).
Second letter, P=Pushrod (ohv)
Third letter R = rear mounted magneto
Fourth letter identifies lubrication type. O= Dry sump with internal double acting pump

In 1931 Sturmey Archer introduced a letter code to identify the user of the engine. CE = Coventry Eagle

Finally, Sturmey Archer started their engine numbers at 101 so by my reckoning this engine would appear to be a 1931 500ohv engine supplied to Coventry Eagle. I think you have a Coventry Eagle.
So far I have found that Sturmey Archer sold engines to Dunelt, Coventry Eagle, Cotton, Rex Acme anf Ransome Sims & Jeffries for lawn mowers!
Cheers,