As destiny would have it, I am in the process of trying to source various motorcycle engine types for demonstration purposes. Varying from single cylinder mini thumpers to BiG V-Twins or On Line Fours. Some single cylinder will be 2 Stroke and others 4 Stroke, so that there will be an array of plenty to launch discussion topics and produce a considerable amount of workshop mayhem show and tells.
However, there is another big problem to consider…how can I bench test these engines to see if they will even start before I begin the strip down to reveal their inner workings. How can I start an engine without having the electrical side of it sorted out too.
In the past when I have performed engine strip downs and rebuilds, I have usually been working from a complete donor motorcycle, so all the electrical is there at hand. All I needed to do was connect it all up and fire it up. If it didn’t then all I would need to do was trouble shoot the electrical or fuel aspects until I found the solution.
But, buying just an engine…or a series of engines, with the idea of making them static viewing pieces in a studio or workshop, is a whole other kettle of fish…as the Germans would say…perhaps?
Every motorcycle needs some way of turning the engine and ultimately the crankshaft over in order to produce the spark at the correct time so that it ignites the fuel in the cylinder. This is achieve either by a kick start or starter motor. So I really need to ensure each engine at least has that in place.
Every engine at the end of the crankshaft has some sort of electrical generation operation with a stator and rotor set up, pick up points, magneto etc.
Elec-trickery occurs here to produce electrical supply outbound to a coil which amplifies the 12v produced by the electrickery to something in the region of 20,000 volts which is sent to the spark plug thus creating a spark and thus igniting the fuel air mix creating life in the engine…or something like that anyway.
Now most modern motorcycles basically operate in this way but may have other components in the middle and afterwards to not only get the timing just right but also how much electricity is fired up to the spark plug.
So the question is, could you bypass all of that with some kind of external contraption that could produce a spark whilst the engine is being turned over and sucking in fuel ready to be set alight? Perhaps the timing of the spark isn’t that critical, as long as it gets a spark?
Well, yes and no. It definitely needs a spark at the correct time however there can also be multiple sparks produced at other periods too…almost wastefully. In fact older engines sometimes employed this very notion too in what was called double or multi fire spark plugs.
So all I would need is a coil that I bought or one that I could make, a 12v battery supply to that coil to a spark plug, and some way of repeatedly collapsing or breaking the power to the coil thus inducing a current along to the spark plug.
Perhaps some kind of rotary striker might just do the job, at least to create a momentary combustion in a cylinder. The major issue is if the combustion occurs at the wrong timing, it would cause all sorts of internal malaise, so perhaps the timing needs to be calculated too.
Perhaps I do not need to be so concerned about generating the power myself but simply apply some form of bypass so that I could just power everything from a 12v battery. This would be easier to achieve with older engines but not so easy at all with modern engines controlled by onboard computers.
I shall be experimenting in the future LIVE sessions and on videos too, but if anyone has some ideas, let us know in the comments. Let’s get our thinking caps on to see what bypasses can be made and what home made solutions can be constructed to fire up an engine at least on a bench.
Over to you…
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