Buchmann Mk III 0.6cc

 

Name Buchmann Mk III 0.6cc Designer Herr Buchmann
Type Compression Ignition Capacity 0.6cc
Production run unknown Country of Origin Switzerland
Photo by Tim Dannels Year of manufacture circa 1945

 

Notes:

It's now well accepted that the first commercialy available compression ignition--aka "diesel"--engines appeared on the Continent around 1940 in (neutral) Switzerland. The "Etha" is generally acknowledged as being the first, but it was short lived and it's the "Dyno" that gained the most fame. But there was another, and that is the little Buchmann 0.6cc side port. The sectioned drawing here appeared in Laidlaw-Dickson's 1946 book, Model Diesel Engines. Dickie does not say a lot about the engine, apart from noting its unusual mounting method and saying that it, unlike the Etha, is (was) still available. It is identified as the "Mk III", but there is no indication that other engines preceeded it.

The "Kratmo" Tutonic heritage is rather obvious from the split crankcase design with the securing flange doubling as the engine mounting lugs. Makes for a rather large frontal area, and I'm not too sure how it would fare in a bad prang, but it certainly is a distinctive feature. The cut-away is more revealing, as it shows how the designer managed to cram a long stroke design into a very small package: notice the crankshaft? It's like a crank-handle. The side opposite the crankpin has been completely turned away. Then, by using a short con rod, the piston at bottom dead center (BDC) descends into the volume normally occupied by the crank web, allowing the overall height to be minimised. The down-side is that we've now purposly created the optimum out-of-balance situation. At 0.6cc, on a slow revving "long-stroke" side-port, this is probably no big deal, but the technique would not scale well (and for trivia buffs, the English "EPC Moth" used a crankshaft just like this too).

The engine in the pictures is attached to Tim Dannels "World Engines" display board. As far as we know, it is completely original and shows some differences from the "ideal" as depicted in the cut-away drawing. First, the venturi-shaped restrictor insert shown in the end of the inlet pipe of the drawing is absent in Tim's example. We doubt that it dropped out as there are no marks to indicate it was ever there. Its usefullness in that locaton would be questionable anyway--you want the point of minimum pressure (the restriction of the venturi) to coincide with the fuel jet to maximise suction, not be halfway to the cylinder up-stream from it. Next, the drawing shows an insert threaded into the cylinder head to carry the compression screw, with a flange inside the head. Neat idea. Assuming the insert was steel, it adds strength to a stressed component. It also adds to the manufacturing costs and is totally absent from Tim's engine, as are the two holes evident in the top of the head in the drawing--presumably for a tightening pin-spannar.

The other obvious difference lies in the shape of the needle and its friction spring. Here are the parts in question. They certainly appear original, so we conclude that this is another consent to the relaties of quantity production. How would you wind a barrel shaped spring anyway? Damned if I can think of any way that does not capture the mandrel for all time--although spring-winders are clever folk, so there probably is a way.

What does transfer quite well from concept drawing to production engine is the "Buchmann" name and spread-wing bird logo on the front bearing casting, although the "BFM III" on the main casting did not. The case casting is rather agricultural, but for all that, it's a little charmer of an engine and I'm rather sad that it lies in Tim's collection and not mine! To remedy this, drawings have been made and one thing's certain, no sand cast case is going to be rougher than the original

 

Ruler

 

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