This is the very first drawing of the Delage cylinder block side elevation, and a section through the first cylinder. It was dimensioned, but this drawing was all there was to work with initially.

This cylinder block assembly sits on the crankcase, and it was very easy to decide to make it in four parts:

o The base plate

o The cylinder liners.

o The water jacket which encloses the cylinders.

o The top component which contains the sixteen valve gear cam mounts, the spark plugs etc. This is a separate part that will drop on the top of and locate on the cylinder liners. This is very similar to the arrangement on the 1:3 Scale 3 litre Bentley engine.

The only problem is in the top component. As can be seen on the section, there are only two planes that are parallel. The other faces are at either at 30° or 40°. This makes it very difficult to work out a datum.

The intention was to have only one datum on each drawing, and all the dimensions would be taken from that datum. A datum, however, was chosen which will be described later.

This is the first machined part of the cylinder block. Here the cylinder liner recesses have been machined. 

There is a parallel ‘fence’ bolted to the machine bed with a stop at the end. The component can then be put up against the parallel, and against the stop.

It was decided to move the longitudinal datum to the centre of the first cylinder.

The component had to be precisely centred on the bed, otherwise once the cutter got to the other end, it would have run out of movement.

The previous photo shows the job finished with the packers and parallels removed. The “threepenny bit” items are Mitee-Bite clamping devices. They fit in the T-slots, and work around an eccentric headed cap screw.

The next stage is to fix the machined base plate onto a jig block, mounted between centres in the dividing head. This allows the plate to be rotated 47.6mm off centre, in order to machine the curves between the hold down bosses.

Using a 4mm ball-end mill, it’s just a question of setting the datum, and then moving it either side and rotating the component back and forth in the dividing head, so that the requisite curve is machined. The process is repeated at each location until the other end is reached.

Using a ball-ended mill results in a bit of a ‘tramline’ surface, but it is easy to dress that off at the end, with a needle file.

Machining the cylinder liners

Simultaneously turning and drilling the cylinder liners, before fine boring and honing to size.

Turning the expanding mandrel to match the bore of the liners.

All the liners are then put on the expanding mandrel. If there are eight liners, nine are always made. The extra one is used as a ‘setter’ which is used to ‘set’ the tool. Then all the liners are run through with exactly the same setting. This means they all come out parallel, concentric and with the correct dimensions.

Any further operations on the eight liners will be done on the ‘setter’ first.

All the liners are fitted into the base plate.

All fit well.

Note the ridge near the base of each liner that will support the water jacket.

Machining the water Jacket

The water jacket is another block of cast iron that needs to be machined, using the same clamping setup as the base plate. There is a lot of machining here, with the Mitee-Bites used to clamp the block against the parallel fence.

Here the access openings in the side of the water jacket are being machined. These will eventually be closed by screwed on water plates.

Hollowing out of inside of the water jacket. The swarf has been cleared away. There was a lot.

This is the resulting water jacket. There’s not much material left, and it’s a bit delicate.

Everything is in line. Using the parallel fence, the stop and the correct datums everything assembles without needing any filing.

Part one here.  Part two here.  Part  three here.  Part four here.

Bentley series starts here.