Mietz and Weiss Restoration


| January/February 1987



4 HP Mietz and Weiss engine

Mike McArthur of 26425 S. E. 39th, Issaquah, Washington 98027 restored this 4 HP Mietz and Weiss engine.

26425 S. E. 39th, Issaquah, WA 98027

Fortunately, when I acquired this four horsepower Mietz and Weiss engine, only one unique part was missing, and Mike Moyers, with his machining expertise, produced a replacement. In addition, the engine had spent most, if not all its life under cover, and in western Washington, that makes a big difference.

During the summer of 1984, with the help of another friend, Dan Grin-stead, I managed to start and run the engine for its first time in many years. We discovered its idiosyncracies and worn parts and then I disassembled it for restoration during the winter.

Some unique features made this two stroke hot bulb engine more of a restoration challenge than any engine project I have tackled so far.

The tank on top holds the fuel which is forced, by a low pressure pump, through a fairly primitive nozzle and the spray hits a blade from the hot bulb that protrudes through the head. The engine will start only when the bulb is red hot. Once it starts the engine slowly builds speed and then runs very steadily as the governor controls the stroke of the fuel pump. I can see why Mietz and Weiss engines won major recognition for running dynamos in about 1900.

The cooling system involves a typical water jacketed cylinder but water is consumed and must be supplied constantly under pressure. A supply line connects to a float box on the side of the block, and as the water level drops, the float allows a valve to open and more water to enter. Water will boil in the block right away and the steam produced rises into the copper expansion dome on the top of the block. Then it continues to rise in the semi-circular brass pipe, where it condenses. This hot water enters the cylinder through a small port on top and is fully compressed along with the injected fuel until combustion occurs. The claimed effects of the water were cleaner burning, increased power, and more even running.