When UM was handed over, its builder told me I would never need to touch the rotary change over valves (high or low compression) which are part of the JP3 one per cylinder. So I havent touched them, and so have never run the engine in low mode. The theory is that for heavy duty work the engine can be set in low compression mode, moving from high compression mode required for starting. I supposed heavy duty mode would be on a pump or generator operating for long periods at high load. Not something the average nb engine would be faced with. However the Lister manual, which I have read today for the first time, uses slightly different wording, and I quote -
Use high for starting and low for normal running. Do not run under high load with high compression. For long runs at half load or less use high compression By reference to the parts list I now understand how these things work. The rotating handwheels are each attached to a threaded valve stem which alters the volume of the combustion chamber, exactly how is hard to see but when the stem is not fully seated in or out the cylinder gases are vented through a small drilled hole. This involves much spitting accompanied by a quaintly pleasing aroma redolent of an engine drivers vest after a high speed run down the east coast line. Anyway . . . we warmed the engine and selected 3x low compression for a miles run at max revs between Fretherne and Splatt. There were some varied puffs of smoke to begin with nothing very worrying, and they soon settled down to clean efflux. So that is that, and I am touching wood, but the engine is as happy as it ever was and vibrates away happily. Perhaps it just had a moody period. Beeky ___________________________________ thorNET, http://www.thornet.co.uk
