Thread: Discussion Model Diesel Engines
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Old Oct 04, 2012, 04:14 AM
brokenenglish is offline
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Sticks, Tissue & old Diesels
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France, Centre, Amboise
Joined Nov 2011
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Derek, That's exactly the point we were making. As a diesel, there's something wrong with your engine!
In 99% of cases, the problem is bore taper. Any engine, to be hand started, needs good crankcase compression to blow the mixture up the transfer ports. On the "quality" early diesels, any bore taper was very slight, machining was precise and they were all hand lapped (only a few seconds is needed), to obtain perfect compression at the top with good crankcase compression at the bottom. People like David Owen, Jon Fletcher, Mike Crisp and Tom Crompton are still doing that today, it's the only way.
Unfortunately, engines like the one you mention are made on modern "glow" principles, with excessive bore taper, so that the bore fit is very tight at the top (which passes for good compression!) and is far too loose at the bottom, and the engine is left to "sort itself out" somewhere between. The result is insufficient (or no) crankcase compression, so that hand starting is impossible. This is certainly the case with your engine. However, using a starter, the high rpm generates enough crankcase pressure to start the engine which, again, is your case I think. But the fact remains that for old traditional diesel lovers like myself, the engine ain't the way it should be! Your engine is a good example. I possess four original Elfin 1.49s and they all start in a couple of flicks... The implications are obvious!
The most frustrating thing for me on diesel-related forums is that many people, unfamiliar with the super old diesels, naturally assume that "modern must be better" (NC and all that), whereas, in reality, most modern diesels aren't a patch on the late forties, fifties and sixties diesels, most of which are still great for flying today!
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