Mietz and Weiss Restoration

By Staff
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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.

Lubrication is supposed to be automatic. A cast iron oil tank
attached to the side of the block receives pressure from the crank
case and with check valves on the oil lines oil is supposed to be
distributed as the engine runs. I have not been able to make this
system work and have added drip oilers.

Speaking of unique engineering of questionable validity, the rod
bearing shells are not pinned and are supposed to rotate freely in
the rod box so that they will wear evenly.

Finally, a few specifications might be of interest. This is
engine number 6438 and I do not know the exact manufacturing date,
but the tag includes several patent dates from 1897 through May
1906. The engine’s rated horsepower is four at 325 RPM’s
and the bore and stroke are 6′ x 6?’. The engine weighs
1700 pounds and has a flywheel diameter of forty-one inches with a
two and one half inch face.

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