Water-Inducted Wonder

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Back side of the Mietz & Weiss, crankshaft oilers in full view.
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Jeff Conner’s 1-1/2 HP Mietz & Weiss, serial number
1988. Jeff’s engine is an early example, built before 1905 when
Mietz & Weiss changed from a manually controlled water
induction system to an automatic system using steam. Mietz &
Weiss started building engines in 1894. Remarkably, this engine has
its original muffler

Seven years ago, after finding a nice 6 HP Witte diesel and
getting it running, I got interested in predecessors of true
compression-ignition engines. I knew about Thermoils, and a few
other early examples, but as I learned more I set my sights on
finding an early hot bulb oil engine – and it had to be small.

Coincidentally, I made the acquaintance of engine collector Don
Clickner, Troy, N.Y., after a fellow employee introduced us. Don
and I discussed our mutual interest in old engines, and I asked him
if he had ever seen any small hot bulb oil engines. ‘Sure,’
he said, ‘how about a 1 -1/2 HP Mietz & Weiss oil

As it turned out, Don had a friend who rescued a Mietz &
Weiss – this Mietz & Weiss – from an old farmhouse before the
house (and the engine) was cleared away as part of a reservoir
project. Don’s friend had passed away, and Don had been storing
the engine for the past 15 years as a favor to his friend’s
family. After telling me about the Mietz & Weiss, Don contacted
the family to see if they would consider selling it to me. To my
great fortune, they agreed, and that is how I came to be the
custodian of this interesting little engine.

Mietz & Weiss Engines

Mietz & Weiss oil engines are two-cycle,
crankcase-scavenged, hot-bulb ignition kerosene engines. They use a
dry, hot-bulb head, the hot bulb initially heated with a torch,
operating at a dull red heat to ignite fuel injected into the
cylinder. ‘Squirted,’ might be a better word than
‘injected,’ as the fuel system operates at very low
pressure. A solid stream of fuel ‘squirted’ into the
cylinder hits a small lip projecting from the hot bulb cavity at
the front of the cylinder. The fuel splatters on impact and is then
swept into the hot bulb cavity by the incoming combustion air,
where it ignites from the surface temperature of the bulb. The fuel
is squirted into the cylinder just after the air intake port is
closed by the piston -there is no precise fuel timing.

In a medium- to high-compression engine this could lead to very
destructive preignition problems. Mietz & Weiss engines,
however, had fairly low compression, normally no more than 60 psi
cylinder compression. Even so, they could knock and suffer from
preignition if everything wasn’t just right, and operator
experience was a major factor in running these engines

With the engine working under load the bulb would run hotter
than when running lightly loaded, leading to preignition. To
counter this, a small trickle of coolant water was introduced into
the intake air, cooling and slowing the combustion process and
effectively combating preignition. On early Mietz & Weiss
engines, a manually controlled water sight-glass was used to add
cooling water to the combustion air stream.

In 1905 Mietz & Weiss introduced automatic water feed to the
combustion air. The cooling system was changed from tank cooling to
a gravity fed, pressurized system that allowed the cooling water to
boil in the water jacket. The venting steam was condensed in a
cone-shaped condenser on top of the engine and introduced into the
intake air stream. It was automatic in the sense that the harder an
engine was worked, the more condensate was fed to the engine.

This was a significant development for Mietz & Weiss, and it
probably saved a lot of engines, as operators had a tendency to
introduce too much water with the early, manually-controlled
engines. Yet as much as this development improved these engines,
high cylinder wear was still a problem. But, kerosene was cheap
(and much less dangerous than gasoline – oil engines found great
favor with insurance companies in the 1900 era), and despite any
drawbacks in their design the low operating cost of Mietz &
Weiss engines was highly touted in glowing customer

Fuel System

The fuel system consists of a piston pump and a number of check
valves, with fuel pumped through a small nozzle injecting a solid
stream into the cylinder. Through linkage acting on the fuel pump,
the flywheel governor controls the stroke of the fuel pump, and in
normal use the fuel pump hardly appears to move. One full stroke of
the fuel pump by hand supplies enough fuel to accelerate the engine
for three or four seconds. This momentary acceleration also happens
when you shut down the engine, because the pump gets a full stroke
when it’s put to the shut off position beyond the travel of the
governed fuel pump actuator. Interestingly, Mietz & Weiss also
offered a hit-and-miss fuel system using a pendulum governor, but 1
imagine it was hard to keep the bulb hot if the engine had a light
or even a variable load applied.

A combination of low compression and poor fuel atomization in
these engines hindered complete combustion, and as a result much of
the fuel that went into one of these engines passed right through –
the white smoke commonly emitted from Mietz & Weiss engines is
the result of unburned fuel. Increased compression and timed,
high-pressure injection did much to advance hot bulb oil engine
designs, but Mietz & Weiss chose not follow the lead of
companies like Fairbanks-Morse, Muncie and others that went on to
produce semi-diesel and diesel engines. By about 1923, Mietz &
Weiss was gone.

Restoring the Mietz & Weiss

Weighing in at 600 lbs, my 1-1/2 HP horizontal, serial number
1988, is one of the smaller engines Mietz & Weiss offered, and
it was meant from the outset to be a stationary engine. Of pre-1905
tank-cooled design, it has a water sight glass to control the
introduction of water into the combustion air instead of the more
common steam-condensing cone.

A good side view of the Mietz & Weiss shows fuel pump, water
sight glass, cylinder oiler, flywheel pulley and, just behind the
flywheel, the governor for the fuel pump. Just visible at about the
2 o ‘clock position is the actuating arm off the governor that
contacts the actuating rod for the fuel pump, Brass pipes at top
and bottom of cylinder are cooling lines, black pipe at bottom is

A closer look at the Mietz & Weiss shows the fuel line from
the copper fuel tank at upper left entering the fuel pump at right.
The line exiting the pump delivers a metered shot of kerosene under
pressure, injecting the fuel into the cylinder where it hits the
hot bulb and ignites. Note the fuel pump shut off lever off to the
left side. In it’s ‘off’ position it pulls the fuel
pump actuating rod towards the fuel pump. In its ‘on’
position the actuating rod is allowed to pull back; a flywheel
governor contacts r; actuating rod to pump fuel The fitting to the
left of th.: fuel pump is the sight glass and water line for water
induction to help control preignition.

When I pulled my engine apart, it was clear it had earned its
keep. The farmer who owned it had kept it sheltered, but he either
used oil sparingly or used a lot of water in the engine, as the
cylinder was too worn to reuse as it was. I also found the exhaust
port was plugged almost shut – a pencil would not fit through the
hole in the carbon plugged in the exhaust pipe. I decided this old
engine should get the works, and so began a three-year

Boring a ported cylinder, not to mention one with three ports,
is no easy task. Joe Sykes at Niagara Piston Ring took on this part
of the project, boring the cylinder oversize to clean it up and
then spray-welding the piston to fit. The brass connecting rod
bearing wasn’t too bad, but I went ahead and reground the
journal and fit a new bearing.

Fortunately, all the engine’s pieces were intact. The
original Michigan four-post oilers for the cylinder and rod
bearing, as well as the original oilers for the main bearings, were
still with the engine. All the bolts were original, and not one had
been damaged in the engine’s long life. The farmer who
originally owned this engine was either a very careful mechanic –
or he never did anything to the engine. I am inclined to go with
the latter.

A small amount of original, black paint was still on the block
in a few places, and there was a gritty, iron powder-like filler on
the block as well. I filled it a little, but I let the texture of
the castings (which are rough) show through.

As my restoration neared completion, I was a little dismayed
with the engine’s apparent lack of compression, but a little
research and discussions with another Mietz & Weiss owner made
me more confident the engine would run okay. Finally, the day came
when there just wasn’t anything else left to do or check, and
it was time to see if it would run.

To preheat the hot bulb, I made a vertical blowlamp out of a
gasoline blowtorch. It worked well, so I put it in place and waited
for the bulb to get red hot. I manually stroked the pump and felt a
slight reaction on the piston. ‘Oh what the heck,’ I said
to myself, and I gave the flywheels a gentle spin. To my surprise,
it started immediately, then slowly built up speed to the point I
realized the new governor spring was a little TOO tight. That’s
when I learned that stroking the fuel pump to the ‘off’
position gives the engine a little boost in speed and a reserve of
fuel to run on for a few more seconds. It was a little
disconcerting, especially while I was trying to stop an already
overspeeding engine.

I adjusted the governor spring, and after loosening it quite a
bit the engine ran nicely at about 350-400 rpm. Nicely, that is,
for a Mietz & Weiss. With the amount of smoke it was putting
out, I think I could have rented it out for mosquito control about
then. Since getting this engine running, experience has taught me
that if you run these engines at their rated speed the bulb usually
stays hot and the engine runs cleaner. At slower speeds, the bulb
cools down and the engine starts skipping. I have found that
leaving the blowlamp on low heat keeps the bulb hot enough to
minimize smoking at slower engine speeds. If you place a load on
the engine, however, the smoke resumes. Kerosene was the designed
fuel for Mietz & Weiss engines, although they advertised that a
wide range of fuels could be used. I would be interested in hearing
from anyone who has tried lighter distillates or any other

I find this a very interesting little engine, what with its
unusual vertical copper fuel tank, large diameter flywheels and
top-mounted brass fuel system. The brass nameplate is a
reproduction off another engine like mine, and I have heard that
many Mietz & Weiss engines were shipped without a nameplate.
Mine showed no nameplate mounting holes and was evidently one of
these. I think it’s fitting to have one installed for display,
but in keeping it original I affix it with magnetic tape so it can
be easily removed.

I was fortunate my engine came with an original muffler. With it
connected, the engine sounds more like a steam engine, producing a
very gentle ‘puff, puff, puff’ sound. Nice smoke rings too!
At shows, the noise of the blowlamp as I heat the hot bulb usually
gathers interested onlookers. Then I tap the pump two strokes and
give the flywheels a gentle spin. It has never disappointed me.

Contact engine enthusiast Jeff Conner at: 8269 Dunham Rd.,
Baldwinsville, NY 13027, or e-mail: jconner2@twcny.rr.com

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