Part 4 by Guenter Kallies

Group No.3: The valve gear

Parts list 

The valve gear system used on the original engine was a complicated lever system which was standard at that time on stationary engines. To copy this on a small scale model means that you have to deal with a lot of very small elements. This was the reason that a more simple valve gear system was selected for the model version. 

The Eccentric sheaves (3.1) should be made as a pair. Starting with a piece of brass Ø20 and 25 mm long, turn both ends to Ø 19 mm over a length of  a little bit more than 5 mm. At the same setting, the groove should be introduced. Now, cut it in two pieces and clamp it into the chuck again, but with an offset of 3.5 mm. This is not really a problem if you have an independent 4 jaw chuck and a dial gauge. Please have in mind that you must read 7 mm on the dial gauge for one full turn. 
If you have only a 3 jaw chuck, don’t worry. A packing of scrap material between one jaw and the work piece will give you the required offset. Check it out with the dial gauge.

The Eccentric strap (3.2) is made either from round bar or, if you have it available, from hexagon brass material. An 80mm length of Ø 3 mm brass has to be silver soldered into the lower hole. The exact length of this rod must be determined on the assembled engine.

The Reversing link (3.4) can be filed to shape with the skill and confidence to do it, but most builders will prefer to use mechanical assistance at least in forming the slot. Cut the slot with a small slot cutter either in the milling machine or in the lathe. The material for the link is soldered or clamped to a bar pivoted on a bolt which is fixed to the milling machine table or to an angle plate bolted to the lathe cross slide. Simply using the bar as a hand lever, it is not difficult to control the required movement. Stops on both ends of the movement give more accuracy. 

A lot of other small items are needed in this group. Not shown in the drawings is the Axle (3.7) which is simply cut to length from round material. All the other components are so simple that they do not need any explanation in detail. Some items are silver soldered together from more than one part. A fixture made from scrap material will be helpful to hold the elements in position during the soldering process. 

Click on drawings to download - for personal use only.

Part one here  Part two  Part three  Part four