Model Review

| August/September 1992

  • Allman engine
    The Allman engine.
  • Radiator connections
    View of radiator connections, and valve cage assembly.
  • Cam gear, hit and miss gear'
    View of cam gear, hit and miss gear. The governor is in the pulley.

  • Allman engine
  • Radiator connections
  • Cam gear, hit and miss gear'

32 South Street, Apt 1 Clinton, New York 13323

The first time I saw the Allman model was at the North American Model Exposition in Ann Arbor, Michigan in 1991. The Allman is the third in a series of limited run scale engine models made by DeBolt Machining. The model is of an inverted vertical, single flywheel side crank engine, with an unusual valve gear and hit-and-miss governor. It certainly isn't just 'another push rod engine'. This engine also sports a cast iron radiator, and a gas tank to be mounted below the floor level. The governor is located inside the belt pulley on the offside of the engine. The connection from the cam to the exhaust valve is an unusual system of rocker arms that wraps around the engine from one side to the other. Some other features include oil lubrication, a ported scavenging exhaust, and a neat looking muffler. It runs on regular unleaded gasoline and Coleman lantern fuel. I prefer the latter, because it doesn't smell as bad (although gasoline has a more familiar smell). There is a small thumb screw on the governor mechanism for speed control.

Since there are no living Allman engines that I know of, and the only reference to one that I have seen is a period drawing reproduced in the American Gas Engines, it is hard to compare the model to the original. I am told DeBolt used patent drawings in their research. The original presumably had a jacketed cylinder. The model has no cooling passages in the cylinder at all. The piping from the (functional) radiator to the engine ends at the cylinder casting in blind, tapped holes. It seems that this arrangement can provide only a token amount of cooling, but I have run my engine for hours with NO water, and the engine doesn't seem to mind. This was done, no doubt, to keep the price of the model down. The original used a gaseous fuel (probably natural gas or producer gas), and hot tube ignition.

The model has a rather conventional fuel mixer, and uses high tension ignition with a 10mm spark plug. This was done to save the owner the hazards and extreme aggravation of hot tube ignition.

I purchased this engine from DeBolt as a mechanics kit. They sent me the engine in two batches of parts. The smaller parts came first, all sealed in plastic, and grouped by assembly order. All parts were CNC machined, including the dome head bolts. The castings, most of which came later in a second batch of parts, were a bit rough, with a few flaws here and there, but nothing that detracts from the operation or appearance of the engine. The model is made of iron and bronze castings and steel and brass stock. A painted, brass tag with a DeBolt serial number was also included. The model is a substantial hunk of iron. It is not as heavy as some I have seen, but it will still build your muscles.

The assembly instructions that came with the model are very brief, and some potentially confusing assembly drawings are relied on to complete the model. The only problems I had were assembling certain parts before others, having to remove them to put other parts on. This is probably due to my chronic reluctance to follow directions. Each part has a drawing and numbered for identification. Drawings for a base are included, as well as timing and wiring diagrams. No photos of the model are included, nor is there any indication of what the overall model will look like when finished. Overall assembly went well, and was completed in the course of a couple of evenings. Tolerances in parts were good, if rather tight in a few places. Some filing was needed to fit some of the parts properly.

Helen Randall-Matthews
2/7/2011 7:49:12 AM

I am the only living direct descendant of Isaac Fox Allman - the inventor of the Allman Engines. I just wanted to say that it is so wonderfully heart warming to see that people are still interested in his work. I'm sure he would be very proud. Isaac Fox Allman was my Great Grandfather, he was born in 1844 in Patterson NJ. He fought in the Civil War and returned home to raise a family, become a Mechanic and then open his own company where he designed Engines among other items. Later in life he sold the Allman Engine Company and retired to Selden, Long Island NY where he Enjoyed his family - including my father as well as the respect of his neighbors and friends until his death in 1910. Many of his original drawings, designs and advertising ephemera have been handed down to me and are still in my possession. I am looking for either an Allman Engine Model kit or perhaps an original engine (even one that needs to be rebuilt) so that I can pass this wonderful legacy down to my Children and Grandchildren. If any one has any information as to where I can locate one - I would very much appreciate it. I can be found on if you have the capability to use the website and I will also watch for comments on this site. Thank you for keeping my G-Grandfathers work alive. Helen Randall-Matthews Orange County, New York


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