Two-Cycle/ Hot Bulb, Kerosene Fueled Water Induction - The Mietz a Weiss Oil Engine Had it AH
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 engine?'
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 successfully.
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 testimonials.
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 exhaust.
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 restoration.
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 fuels.
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: firstname.lastname@example.org