David Auld was a steam toy maker in New Zealand. He only made one type of roller so it has no model number or name. It's just known as the David Auld Steam Roller. From it's appearance, it is very obviously a toy but it is very sturdily built and has some interesting design features.
The original meths burner is similar to a Mamod vapourising type but is different in that most of the length is blanked off. This means that it should have a small flame which should last a long time. It sits under the boiler with the exposed section of the mesh located under the centre of the boiler, with insulating material between the flame and the sides of the firebox/chassis. The boiler is a simple pot type; 45mm diameter x 185mm. It has a safety valve, steam feed and chimney. The steam is fed directly to the engine block.
The engine block is a solid lump of brass supported at one end by the steam pipe and at the other end by a strap wrapped around the boiler. Built into the block is a valve which reverses the feed and exhaust connections to the cylinder, thus reversing the engine. It also provides some speed control.
The cylinder is a single acting oscillating type; 7.8mm bore x 22mm stroke. The crank is a simple bent end on the crankshaft. The crankshaft is supported in a long tubular bearing with an oil hole in the middle. At the other end of the crankshaft is a mazac flywheel 40mm diameter. The hub of the flywheel has a groove for a drive belt.
The drive belt goes from the flywheel to a large pulley on an intermediate shaft. This intermediate shaft has small rubber wheels on each end which bear on the rims of the two rear rolls. The shaft is fitted into slots in the chassis and is spring loaded so that the two rubber wheels are pressed against the rolls, thus providing a reliable friction drive.
The paintwork appears to be original and is in reasonably good condition, apart from the flywheel and the rims of the rolls, which is to be expected.
As acquired, using the original (I assume) burner, the engine is a very poor performer. The small flame appears to be insufficient to maintain a good boiler pressure. I have obtained another burner which fits and produces a much larger flame, but not as long lasting. The engine runs ok with that one so I use it for running and the original for display.