The coolant circulation was based on the good old, tried & true, 'thermo siphon' principal. Hot water from the top of the head rises & is replaced with cooler, & therefore heavier, water from the bottom of the drum.
It is important for the bottom of the drum to be at least level with the bottom of the coolant jacket, or a little higher. for it to establish an efficient circulation, & the top of the radiator, or coolant resevoir [drum] must be higher than the top of the engine &, within reason, the higher the better.

This engine has no separate cylinder head & the block & head are cast as one unit. The valves are accessed by removing the two large brass plugs in the head & one of these is made to accept the spark plug, which is usually placed over the exhaust valve, not the inlet as this one has.Quote:
It is a spark ignited engine, not a Diesel, as can be determined from the carburettor, the spark plug & the plug lead. It's also a 13 gallon drum, not a 44.

These things ran close to boiling when working hard, which was good because they ran on poor quality petrol or even Power Kerosene which needed quite some heat to make it vaporise properly & run well.

Early engines used an automatic exhaust valve actuation with an atmospheric inlet valve. Worked perfectly.

as it has no water pump is it gravity fed water??

Have a good look lads this is one of the first water cooled engines .The steel tub is the radiator and it has no water pump .
Can you guess how it works ?