Mining for Gold: A Rare Stover Model U Gets a Makeover

A 1913 8 hp Stover Model U used for crushing gold and silver in the mines of New Mexico is restored and running.

By Staff
article image
by Mark Winscott
Mark Winscott's 1913 8 hp Stover Type U.

1913 8 hp Stover Type U

Manufacturer: Stover Manufacturing & Engine Co., Freeport, IL
Year: 1913
Serial Number: OE50391
Horsepower: 8 hp @ 300rpm
Bore & stroke: 6in x 12in
Engine Weight: 2,300lb
Flywheel dia: 42in x 3in
Flywheel Weight: 373lb
Ignition: Igniter w/coil and battery
Governing: Hit-and-miss flyweights
Cooling: Hopper, 15 gallons

Gold nuggets are attractive to most folk, as is silver ore. A lot of effort has been expended to find, grind and sell gold and silver. Precious metal mining in central New Mexico has a short but diverse history, stretching from the ghost town of Bland, New Mexico (including the better known Albemarle Mine), south to Los Cerrillos, on to Madrid (where coal was mined for heating nearby boilers for power) and farther south to San Pedro. The smaller San Pedro mountain chain south of Santa Fe was the site of many precious metal mining claims in the late 1800s to the early 1900s. Many “one-lunger” engines, likely melted down for their steel once their work life was over, were employed in the day to power air compressors, mine hoists, rock crushers and electrical systems.

The Stover

This 1913 8 hp Model U Stover was purchased for the intent of crushing gold and silver ore from the San Pedro Mine in the then-bustling San Pedro, New Mexico, mining community one year prior to the start of World War I. It was manufactured in Freeport, Illinois, shipped through the John Deere Plow Co., Kansas City, Missouri, and then arrived in San Pedro.

It is suspected that the engine also powered water pumps for removing water from deeper shafts. Today, some of the shafts are full of water. Sometime around 1950, the engine was moved 5 miles to a Hyer, New Mexico, cattle ranch to pump well water. Then around 1985, the engine was moved to its current site at Camp Oro Quay, New Mexico. The camp retains some artifacts from the mining era for youth educational purposes. Staff and kids have really enjoyed seeing and studying this antique, now restored and running. Few schools today have an engine or shop class that would teach engine operating mechanics. The Stover has an open-crankcase, allowing camp staff to teach interested kids how an engine operates.

Engine inventory

Due to its age and multiple use locations – and who knows how many operators – the engine had been pillaged for brass parts and experienced several cold weather freezes. Given the Model U’s rarity, we’re fortunate to have it around and in working condition.

The flywheel-driven Wizard dynamo, fuel pump and exhaust pushrod were missing. Also missing were the rocker arm, igniter trip assembly, cylinder/wrist pin oiler and the priming cup. The connecting rod bushing was missing, as were the crankshaft bushing grease covers. Oddly, the original wrist pin brass bushing was still present.

For a period of time, likely months, water had remained trapped in the horizontal cylinder, 1-1/2 inch deep. Corrosion evidence and pitting on the piston crown, cylinder wall, head and intake valve faces can be easily seen. The 6-inch x 10-inch piston measures 5.965 inches at the crown and 5.993 inches 1 inch up from the skirt; a draft of less than 0.1 degree!

The as-machined original cylinder measured 6.025-6.040 inches. The cylinder developed scabs that could be dislodged with a fingernail. The scabs were 1-3 inches long, about 0.5 inch wide and 1/16 inch deep. Since they were in the piston stroke region, cylinder re-sleeving would be required.

A raw ASTM A-48 G2 cast iron cylinder was obtained from Dura-Bar in Woodstock, Illinois. Dura-Bar already had the correct A-48 gray iron and rough size in stock. Without the help of Dura-Bar’s Al Kendall, this engine would still be a roosting spot for birds in the yard.

Triple H Pumps and Engines of Lovington, New Mexico, machined the new sleeve and bored the cylinder. Without their help and expertise in large-diameter boring this Stover would be yard art. Sam, the machinist, did the boring on a Berco vertical boring machine – a machine we’d recommend using doing this work. A total of 0.10-0.15 inch was removed from the cylinder for cleanup. It took 9 tons of pressure to push the new 20-inch sleeve into the bored-out cylinder.

The resulting clearance from the piston to new cylinder wall is greater than 0.03 inches at the crown, but approximately 0.008 inches between the piston skirt and wall. The overall cylinder length is 24 inches, but the 4 inches from the head to below the igniter port is never swept, so the sleeve was made to a 20-inch length, which encompasses the top piston ring extent, while not boring into the igniter port.

The 104-year-old piston had seen some hard use, to the extent its ring grooves were badly trapezoid-shaped. The grooves were squared on a lathe, which resulted in four different groove widths. Noting the existing porosity in the wrist pin hole, the skirt fractures and existing ring groove pits, the least amount of material was removed for a square cleanup and four custom cast iron rings were purchased from Mary at Niagara Piston Ring Works. The ring end gaps were adjusted against the new cylinder sleeve (0.012-0.015 inch) and installed on the piston. The old ring gaps measured 0.065-0.075 inch. The groove-to-ring width gap was measured with a feeler gauge at less than 0.003 inch, per each groove. The piston skirt edge shows micro-fractures, which may be from use or 1910 casting practices. Those have not been brazed or welded, by choice.

The cylinder head and water hopper have had their freeze cracks brazed. The head’s crack was right across the outside face, necessitating a new brass exhaust valve guide. The hopper’s cracks were at the 4, 5 and 8 o’clock positions, looking into the cylinder. The valve seats were also re-cut.

More work

The camshaft boss had cracked into several pieces, but has now been properly welded together. Credit goes to Scot Cushman (a descendent of Everett Cushman) for welding these pieces back together. A new lower connecting rod bushing was also designed and made by Scot and the finished pair – along with the camshaft boss – looks really nice!

We found the engine with its crankshaft journals in an un-shimmed state. New shims for each side of each babbit bearing were fabricated and stacked. There are now eight custom-fit steel shim stacks in the engine.

The replacement exhaust valve pushrod, igniter trip assembly and exhaust valve rocker arm were designed and fabricated by Jim McQuatters. He did a great job, especially since he had no original pattern.

After all the parts were in place, Jim mentored us in setting the timing, troubleshooting and getting the engine running. Jim has adapted a 12-volt engine starter for use on starting bigger engines, and especially diesel 2-stroke and hit-and-miss engines. As it took multiple efforts to start the engine and troubleshoot why it wouldn’t start, the starter came in very handy.

An oops

The author does not care to talk much about this next situation, but a hole was accidentally bored in the piston’s crown. Anticipating that someone else has made this mistake, exhibited here for educational purposes is how we fixed this one.

The hole intercepted the two gussets on the inside of the piston. Whatever remedy was to be employed it needed to avoid heat, mechanical stress or extreme vibration, and not add to the overall weight of the area. After much deliberation and research, we decided to tap the remaining 0.50-inch thick porous piston crown to 1/2 x 13 TPI coarse thread and screw a steel plug into the hole coated with 3M DP420 epoxy.

Two holes were then drilled opposite each other, so that half of these holes would be in the steel plug and half in the piston cast iron. Then, two set screws were threaded in, 180 degrees apart, and coated with DP420. The two set screw holes were not drilled through or tapped through so that the screw threads would impinge against the tapering thread, against the 1/2-inch plug and the piston material. As of this writing the engine has three solid hours run time and no epoxy deterioration has been observed.


We were not initially successful in starting the engine. It had compression, fresh fuel, air, correct timing and spark. After playing that round-robin game a few times, we focused on the spark, because there was no “pop” or even a back-fire regardless of ether or fuel mixtures used. The igniter would spark off the engine and in hand and manually tripped (momentarily closed, snapped open). The question was then, is the igniter sparking inside the cylinder cavity?

Slowly rotating the 42-inch flywheel and observing the tripping process, we watched the trip lever contact the hammer, and then the hammer would snap back. Then we manually closed the hammer against the anvil and checked continuity; good! Still no boom, though. Therefore, we zoomed in on the hammer and anvil motion. We watched the trip lever push the hammer around and make contact with the anvil, but the trip would release before the anvil began to rotate; adjust timing.

Now the trip rotated the hammer, the hammer contacted the anvil and rotated maybe 1-2 degrees, then the trip would release the hammer. This confirmed that the points inside would momentarily close, then snap open making a spark! It was assumed if the hammer was rotating and getting close to the anvil, that the anvil had closed points building up a current – not so: The hammer was snapping back to its resting spot without contacting the anvil.

Now, with the fuel, choke and battery all set, the engine was rolled over and it fired! What a relief.

Today, the engine runs on either gasoline or propane. The igniter is battery and coil operated. A lack of funds has prevented us from obtaining a dynamo for originality. It would be nice to have the associated fuel pump and igniter trip assembly re-cast for authenticity, as well. Maybe those items will come later.

Many folk played a part in getting this engine running again. Without Jim, Sam, Scot and Al, the engine would only be a monument.

Lessons learned

As this project progressed, and knowing that we’re dealing with parts that can’t be easily or inexpensively fabricated, it became very apparent we needed to handle the parts with increased care. Where any machining had to be done, porosity pits were discovered in the meat of the metal. A crack or fracture can occur in any spot with any type of slight mishandling. These parts, as with other machines from the same era, suffered from the state of the art of casting practices of the time; be aware.

If an engine has to be outside and exposed to the atmosphere, orient the engine with the head end up a few degrees to allow any moisture in the cylinder to eventually run out through the rings. A small vent would be necessary to balance the air pressure. Leaving the primer cup valve cracked some would help. We realize an engine being outside and uncovered is not the best of options, but a slight tilt of the head above the horizon may have saved having to re-sleeve this cylinder. Lastly, be aware of how deep you’re drilling. You may not have the thickness you assume. If you know of another 8 hp Stover Model U, we’d be interested in hearing and knowing about it.

Contact engine enthusiast Mark Winscott via email at:

  • Updated on May 18, 2022
  • Originally Published on Jul 10, 2017
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