If you are way out the back of nowhere, a long way from civilisation, there are few things so comforting as the sound of a diesel engine on tick-over; if you are in a car or truck that is. If you are on a motorcycle the probability that you will have the comfort of a diesel engine’s reliability is small. Diesel engines tend to be at their best when they are being used for big industrial uses such as in ships and boats, trucks, cars, and electricity generation. As the diesel engine gets smaller so the advantages tend to shrink also. Part of the problem of making a diesel small can be understood just by comparing the diesel compression ratio to that of a similar sized gasoline engine. A gasoline engine tends to have a compression ratio somewhere in the ball park of 8:1 up to about 10:1; a diesel engine tends to have a compression ratio of around 18:1 up to 20:1 or more.

That much higher compression ratio is needed to cause the fuel/air mix to ignite without the need for a spark plug but as you can readily imagine the crankshaft, con-rods, pistons and the engine’s transmission all have to cope with not only that higher compression ratio but also the higher shock value of the power stroke precipitated by that compression ratio. This means that the engine needs to be more strongly constructed, and that the transmission also needs to be specially constructed because of the different forces that engine will impose on it. More strongly constructed means physically heavier, to achieve that extra strength is going to require more metal and more metal means more weight. So, if in a motorcycle we are trying to keep the weight down as much as possible why would anyone want to install a heavier diesel engine in one?

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