The TH aka Triad engines used lost foam casting technology. The heads, cylinders, intake manifold, and upper crankcase half were cast as one piece. it uses overhead cam with a timing belt. The way the engine was made they couldn't mold the cast iron cylinder liners into the block at casting, so they were bored and pressed in from the bottom, which is the way the pistons and valves have to come out. The problem with the engine was when the engine overheated due to debris build up in the engine, which it did, it would overheat the cylinders, the liners would become loose, and move down slightly, at that time the top piston ring would get above the liner and slam it into the crankshaft, which in turn would break both rods.
There is a lot of the parts that are no longer available for this engine. I had one come in last year on a walker, that needed the timing belt replaced, The timing belt also runs the oil pump on this engine. The problem with this engine was the oil pump gear turned about 1/4 turn on the shaft. The oil pump gear is not available.
