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Jörgen Nilsson Gothenburg / Sweden Jörgen [firstname.lastname@example.org]
I have been fascinated by engines as long as I can remember, finally I have now designed & built one myself.
As my workshop resources are limited to a small lathe with a milling attachment it had to be something simple to learn the tricks of the trade…..
Horizontal air cooled four stroke engine with push rod operated OH valves
After some months of experiments & modification the engine now runs very nice on plain unleaded gasoline.
Initially I used a starter cord, but after some tuning she now she starts with one or two flips on the flywheel.
The air cooling works good, cylinder head temperature stabilizes at about 100 centigrade after 5 minutes running
The idea with the piezo ignition I got from Jan Ridders (http://heetgasmodelbouw.ridders.nu/) but I myself have added a rotary switch to get a better spark.
The function is as follows: During the compression stroke the piezo chrystal is compressed by an ignition cam on the camshaft. However, there is no spark as the piezo is yet not connected to the spark plug.
When the piston is approaching TDC the rotary switch on the crankshaft connects the piezo to the spark plug and a short and intense spark is emitted.
By turning the “stationary” part of the switch it is possible to adjust the ignition setting while the engine is running.
Turning the flywheel by hand at a speed as low as 30 rpm I still get a very good spark, so I think that this explains why the engine is so easy to start.
(There was lawn mover engines made by Clinton USA in the 1960:s using a piezo ignition with a rotary switch. I do not know why this type of ignition never became popular, perhaps was solid state electronics cheaper…. )
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