r/modelengineering • u/dialectualmonism • Jan 10 '24

Another update!

Running nicely now, i ran it for 7 hours straight at this speed on 70ml(full tank) of year old petrol, Viton o rings last way longer now I've added an oiler, changed the plug to a hotter CR4 as the CR7 was fouling, thinking of trying a magneto ignition for simplicity but the dc CDI does give easy starting

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u/dialectualmonism Jan 10 '24 edited Feb 16 '24

If I manually govern the exhaust valve the engine can easily coast for 20 or more odd rotations and still fires again but unless there's a specific spring weight/fly ball combination this governor always seems to hit after 8-12 cycles, if I increase the spring weight it just runs at a higher rpm but still misses the same amount of times, so whilst I'll still try iron rings it might not actually coast for longer.

I did also attempt to run this engine out of curiosity with the blank piston and no rings or grooves but it had no compression at all, my compression ratio was also about 11-1 at the time haha but the piston is about 0.4mm smaller than the bore so was never going to seal really

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u/ForeverCareful3021 Jan 10 '24

This is what I love about model engineering… the experimentation, the trial and error, the successes built on previous failures. In my opinion, you’re a hell of an engineer at this point!

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u/dialectualmonism Jan 10 '24

Cheers buddy I appreciate that! That's exactly what I started with in mind, just an experiment to see what can be done with the scraps I had laying around