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Ainsworth Abbott's huge semi-diesel engine

Updated: Dec 22, 2020

In 1919, just over a hundred years ago, Ainsworth Abbott and Joseph J. Smith went into partnership and for $7000 bought an old mill that had been operated by various members of the Johnson family for most of the previous century. The mill sat on what was then known as Bowman's Branch, a tributary of lower Delaware's Mispillion River. Most of the river forms the boundary between Kent and Sussex counties and the stream is now known known as Johnson's Branch. Abbott soon bought out Smith's share and operated the mill alone for over 40 years until he retired in 1963.

There are four other millponds on the short Mispillion River and old 1868 maps indicate that three of them supported both a grist mill and a saw mill. Abbotts Pond however, being on a tributary, has barely enough water to operate the one mill, which originally consisted of two 48" stones, one for corn and the other for grains. In the late 1800's a Wolf Company roller mill was added because of the demand for a much better grade of "pure white" flour and both stones were then used to grind corn.

With the competition from several other grist mills within a three mile radius, Mr. Abbott couldn't afford to have his business down for very long because of insufficient water, so in 1925 he found a used 1919 Fairbanks-Morse 20 hp semi-diesel engine at the Farmers Supply Company in Arbovale, West Virginia. He purchased the engine for $550 which included shipping from Cass, W.Va. on the Chesapeake and Ohio Railroad. It probably arrived at the freight depot in nearby Milford and from there the 3400-pound engine must have been loaded on a sturdy freight wagon and hauled by a team down four miles of dirt roads to the mill. It was then somehow unloaded and was installed on a concrete pad on the downstream side of the mill. A 6 foot section of the basement wall was then knocked out to give access to the main driveshaft. A dog and spline clutch in the driveshaft separated the roller mills from the mill stones when the engine was running.

A couple of years later, after the engine was operational, Mr. Abbott had a two and a half story addition built over the engine and that's where it has sat for the past 95 years. In 2017 when it was decided to restore the engine the only repair necessary was to rebuild the fuel pump, work that was donated by Diamond State Machining in nearby Farmington, DE. We also had to cobble together pieces of several 8 inch wide drive belts to make just one that was long enough.

The main differences between a standard diesel and a semi-diesel is that semi-diesels have a lower compression ratio and they have a bulb in the cylinder head that must be pre-heated with a kerosene (or propane) torch for about 20 minutes. After the engine is manually started the torch can be removed. Manually means that the large flywheel is spun around backwards and bounces off of the compression, which then spins in the correct direction. After a little practice the engine can usually be started on the first try. Often mistakenly called a hit-and-miss engine, this type Y, Style H semi-diesel actually fires with each revolution, about 350 times a minute.

An interesting feature to Ainsworth Abbott's huge engine is the automatic cooling system. The engine has a water jacket and water is supplied by a pitcher pump on a well right beside the engine. A belt running off of the main engine shaft turns an eccentric pulley. A long arm is attached at one end to the pitcher pump and the other end rides on top of the eccentric pulley. By this means, whenever the engine is running it is constantly pumping water out of the well to cool itself. At the same time the horizontal 6” exhaust pipe blows large smoke rings across the mill tailrace.

A short video of the engine can be seen on Youtube at "1919 Fairbanks Morse 20 hp engine" :

The engine is run for a couple of hours during the scheduled mill tours each month on the third Saturday, from March through November, 2:00 to 3:30 pm. Tours are free for Delaware Nature Society members and $5 for all others. Special group tours can be arranged for most anytime by calling the Abbotts Mill Nature Center at 302-422-0847. (During these Covid times tours are limited to four guests at a time and masks are required.) Previously published in "Old Mill News" - Fall 2020

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