The crankshaft jounal for the connecting rod was finished by lapping with a home made tool.

The temporary wings cast on the end of the crankshaft for turning were removed and the shaft ends turned to size. Even though the shaft was located on lathe centres, there was a small amount of chatter as I was turning the ends of the shaft. The addition of a fixed steady eliminated the chatter.

The shaft diameters for each pulley/eccentric were stepped for ease of assembly so the inner most one slid over the outer one and did not require pressing over it.

Keyways then cut with one end clamped to jaw in a rotary table and the other supported in a lathe centre. (Again, special tooling had to be made to raise the fixed centre. Making tools took longer than the actual machining of parts).

Thanks Dave,

I have received lots of helpful information from members and just returning the favour.

Paul

The eccentric straps could not be held in a lathe chuck because of their shape so make a simple jig to machine the final bore. I use a dial indicator to locate and clamp it approximately on centre and then bored it to size. As the running surface is the smaller diameter, it could simply be bored thru and easily measured to achieve the exact size.

The outer groove was then cut on the outside edge. Then the strap turned over in the jig to machine the groove on the opposite side using the DTI to centre the strap in the jig. This diameter only requires clearance with its mating part, and a small inaccuracy with running axis is not critical.

Eccentric Boss

The design for the 2 eccentrics on the supplied drawing had them both as part of the same part but I made mine as two separate units with a dowel pin setting the angle between them.

The outer shape of the eccentric was turned on the late. (checking for a running fit with the sleeves). Locating the position of the offset hole for the shaft and dowel hole is difficult on the lathe, so I transferred it to the mill and used a rotary table and the digital readout on the table.

Then moved back to the lathe and held the eccentric on centre while tightening the 4 chuck jaws. The hole for the crankshaft then bored to finish size.

Piston Head and Piston Rings

Piston rings were turned from a solid piece of cast iron round bar. A bore gauge used to accurately measure the cylinder and the rings made for a sliding fit. They were then parted with a Dremel grinder.

The rings were very tight when I tried fitting them in the cylinder. On checking the bore diameter, I found that the cylinder liner had been compressed at each end as a result of the heat/shrink fit with steam chest and had to be honed to the correct size.

The rings were cut with a grinding wheel on a Dremel leaving a 1mm gap.

Spring action in the rings made by expanding them over a piece of 6mm rod and evenly heating with a blow torch until they fell off, resulting an enlarged gap of 4-5mm.

Stephensons Valve Linkage

The valve linkage was modelled in 3D to check clearances in all positions of its motion. Solidworks models can be automated and the crankshaft rotated which in turn moves the linkage arms and opens and closes the slide valve. The reversing lever can be moved to reverse the action of the slide valve. Very handy for checking slide valve/port overlap dimensions.

The quadrant link was laser cut from plate and faced on the mill to finish size then the holes for pivot pins drilled and reamed. A mounting plate to extend clamping face of the rotary table was made for holding the links. A CAD drawing with dimensions for the pivot point and for the hold-down bolts made the location of the link easy. With the axis of the RT set at 0,0 the required radius for the slot in the link could be made. The end of the mounting plate was held captive in a slideway, top and bottom and rotated by a lead screw at the end. (The radius was too big to rely on the worm in the RT).

The middle piece made in a similar way but because of its smaller size and only one hole, I made it twice as long and cut it to length after machining.

Compensating Centre

The compensating centre (differential) is normally made from a casting but this was missed when I ordered the other castings for my engine. The original order was sent to Australia by sea freight and the extra weight would not have increased the delivery by much. Sea freight cargo has to be sent in a large wooden box so it can be loaded by forklift. It also has to be fumigated making it expensive.

It is a large, heavy casting which sells for about £120 but would have cost another £160 for air freight. Too expensive, so I fabricated my own from plate and hollow bar.

As well as designing a fabricated version of the hub, I modified the lubrication arrangement. In the original design, a pipe was used to carry oil to the drive gear bush and a hole in the casting to oil the pinion gear shaft. As the gears and bush rotate slowly, I prefer to use grease. Oil lubrication without shaft seals is messy and drips onto the ground. (and my driveway).

A hole in the centre of the pinion gear shaft carries grease to both bushes. Access to the grease nipple is thru the holes for the wheel locking pin. The pin is removed and outer gear rotated slightly to expose the grease nipple. The nipple also prevents the shaft from rotating.

Left: Preliminary machining of hub prior to welding hollow bar, Middle: Final machining, Right: Drilling and reaming holes for bevel gear shaft