Part 5 by Guenter Kallies

Group No.4: The crank shaft and connecting rods

Parts list

While the crank shaft on the original engine was obviously forged, the model version is assembled from various components. Due to the requirement for a functional model, a Flywheel (4.8) was added. There was, of course no need for one on the original design because the two paddle wheels installed at each end of the Crank shaft had the effect of flywheels.

Another deviation from the prototype is the use of needle bearings on the crank shaft. This type of bearing reduces friction considerably when the engine is running.

For the Shaft elements (4.1)(4.2) and (4.3), ground stock material like silver steel or, even better, stainless steel should be used. The Crank webs (4.4) are made from brass. It is not so important to keep the 20 mm hole distance but it must be equal from one to another of the four parts. It is advisable to solder or clamp all the parts together temporarily to drill and ream the holes in one path. The crank webs are fixed to the shaft ends using Ø 2 mm roll pins or split pins. Don’t forget that one crank must have an offset of 90° to the other.

The Bearing housings (4.5)(4.6) should also clamped together, but with one or two layers of paper between both parts. The holes can now turned out on the lathe with the assembly fixed to the faceplate. When the paper is removed, a clamping action is achieved to hold the needle bearings. The outside shaping of the top cover can be done using the same tools as used on crown plate. The Flywheel (4.8) , the Spacers (4.9)and the Oilcup (4.11) are simple turning jobs which don’t need explanation.

Flat brass 20 mm x 10 mm is a good starting point for the Connecting rods (4.10). Bolt a length of 10 mm onto a piece of 65 mm using two M2 screws. Centre drill both ends of the assembly and turn to size between centres. Cross drill and ream the head and the bottom part. Turn over the side face of bottom parts held on the faceplate of the lathe. The last operations are slotting of the head and drilling and tapping the oil hole in the bottom part.

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