The HK30 was a three hp four-stroke engine made in the early 1970s. It was a Lauson design (a subsidiary of Tecumseh). Because of import restrictions at the time, the ones sold in Australia were nearly all made here under licence, by Kirby, so they are commonly called Kirby-Lauson engines. They were quite durable engines.
The crankcase drain plug is a horizontal plug right at the center of the very base of the engine, clearly visible in your first picture - the front view of the mower. It is just below, and to one side of, the plastic oil level plug. It has a square head, and screws out. I will be surprised if the drain plug is not made from steel. A plastic drain plug would not be a workable concept, because of the crud and garbage that drains out with the oil, and gets in the bottom of the thread. If you put a plastic drain screw in, it would be destroyed very quickly by the crud.
The recommended oil was SAE 30 viscosity, to the automotive standard of the time (MS). Single grade automotive oils are uncommon these days, but you might find, say, a 20-40 oil that would be fairly suitable. The old MS designation is long gone - a modern oil would be SF or SG standard. I'd avoid using a 10-30 or 10-40 oil if possible, since the engine will have huge clearances by now and the very thin base stock would probably result in heavy oil consumption, maybe even some smoke.
Last edited by grumpy; 21/01/11 10:40 AM. Reason: Add oil detail
