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Ainsworth Abbott's HUGE Semi-Diesel Engine

In 1925, almost 100 years ago, and not long after Mr. Abbott bought out his partner,

he must have realized that his waterwheel didn't supply enough power or speed to properly operate his roller mills.

The mill sits on Johnson's Branch, a tributary of lower Delaware's Mispillion River. Most of the river forms the boundary between Kent and Sussex counties and Johnson's Branch (then called Bowman's Branch) is just one of it's many tributaries. There are four other millponds on the short Mispillion River and this old 1868 map indicates that three of them supported both a grist mill and a saw mill.

1869 map of the NW corner of Cedar Creek Hundred The arrow indicates where the mill is, owned in 1868 by William H. Richards

Abbotts Pond, however, 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 for sale by 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. $550 was a lot of money in 1925, equivalent to over $9600 today.

The engine 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 5-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 he used it for the next 38 years.

The engine is snug in this wing in the back of the mill

It then sat idle for over sixty years, but in 2017 when it was decided to restore the engine, few repairs were necessary. The main thing was that parts of the fuel pump had corroded and it needed rebuilding, work that was graciously 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.

When the belt then proved to be slightly TOO long, we added an idler pulley, so what you see above is not 100% original. Shhh, don't say anything.

It's important to realize that the engine doesn't operate the entire mill. The clutch in the driveshaft disconnects the engine from the turbine and the millstones. The engine runs much too fast for the millstones, but is perfect for the roller mills. On the other hand, the turbine turns the millstones at the correct speed, but barely has enough power to operate the roller mills at all, and certainly not at the proper speed.

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 8” 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" or

Normally the engine is run for a couple of hours during the scheduled mill tours each month, but with the mill temporarily closed for visitors, it's just run several times a year to make sure everything is working well.

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