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Junkers CLM

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Roger B:
A Junkers pattern opposed piston 2 stoke diesel has been on my build list for some time. I now think that I am close enough to getting my horizontal diesel to run to start on the design for this.
The prototype is the smallest of these engines with 65mm bore and 90 + 120mm stroke which was used in tractors and boats and was manufactured under licence by CLM in France.

There are a number of interesting design features:

The unequal strokes are supposed to allow better port timing. This will require some simulations to reach a suitable design.

The scavenge pump is mounted on top of the top piston and is square. I think this will have to be redesigned round even if this reduces the capacity.

The top of the liner is unsupported and the ports open directly into the crankcase.

The top bearings on the pullrods are ball races, I assume due to borderline lubrication

I am basing my design on a 25mm bore which gives strokes of 35 + 46mm. This will give a liner around 135mm long which I think I can bore using an idea from Jason B of an asymmetric boring bar mounted between centers and the liner clamped to the saddle. The crankshaft also appears possible. Checking on the lathe the clearance over the cross slide is 33.5mm rather than the 31mm in the manual. That extra 2.5mm will allow me to use a chucking piece supported by the tailstock.
I do also have the option of reducing the bore to 20mm but from the diesel point of view the larger the capacity the better.

I am planning to fabricate the cylinder block and crankcase from steel rather than carve it from aluminium so I need a bit of welding practice first.

The outline design is attached in .dwg and .pdf

Hi Roger,
looking good, I am ready to watch every posting.
What a challenge.

Good luck Roger  :)


Ye-Ole Steam Dude:
Hello Roger,

Very ambitious project, I to will be following along.

Have a great day,

Same here Roger. should be a great project!!



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