Trials & Tribulations: 5-Year Dempster Engine Restoration

By Staff
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1920 1-1/2 hp Dempster Model 1K
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The 1-1/2 hp Dempster as found, looking a bit worse for wear but fairly complete.
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The stripped engine base was fitted to the new cart.
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Before getting a fresh coat of paint.
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Garry Anderson turned the axles for the Dempster's cart on his lathe.
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The broken igniter bracket in the process of being repaired.
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Getting ready to fit the cylinder head.
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Fitting the crankshaft to the almost assembled engine.
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It took five years, but the Dempster finally came together.
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The Dempster running. Note the gas tank, made from a Coleman lantern.

The email note came unexpectedly in October 2012 from a nearby engine collector I’d never met. Randy Aldous had a Dempster Mill 1-1/2 hp engine he’d found on a farm in Aberdeen, Idaho, as a teenager and had hauled around for 55 years, never having had the money or time to restore it. He had read my story in the October/November 2012 Gas Engine Magazine, “A Farm Team Resurrected,” of the restoration of a 1917 Fairbanks-Morse Z and its companion Typhoon pump, and wanted to know if I would be interested in the engine.

A Vietnam veteran, Randy was at the tail end of life with advanced cancer, and didn’t want the old engine that had been a lifelong companion to go to the scrapyard after he died.

Well, of course I said yes and went down to see Randy and his engine. I was not familiar with Dempster engines, but I could immediately see this would be a challenging restoration! It had been sitting outside exposed to the elements for many years. Besides being heavily corroded and seized, many parts were missing. Yet I simply didn’t have the heart to say no, so I made arrangements to bring the sad old engine to my shop in Idaho Falls, Idaho. I learned later that Charles Randall “Randy” Aldous passed away only a month after our meeting.


The Dempster Mill Manufacturing Co. started in 1878 in Beatrice, Nebraska, making windmills and water-pumping farm equipment. Their first gasoline engines were 2-cycle models and were introduced around 1898. The 4-cycle engines were introduced after 1900 and looked similar to early Olds engines, with a vertical, box-like water hopper. Engines manufactured up to about 1922 were typically igniter fired using a right-hand mounted Webster Tri-Polar Oscillator magneto, after which they apparently went with the popular WICO magneto.

After more research, I confirmed this was a hit-and-miss, igniter-fired Dempster Model 1K, 1-1/2 hp engine, serial number 12897, manufactured about 1920. An exact date is unknown as there is no Dempster engine registry. Fortunately, this is one of the more common Dempster engines. I made an inventory of missing parts and sketched out a restoration strategy for this rusted engine remnant. I reached out to collectors from GEM, Smok Stak and HitNMiss to glean advice and develop sources for procuring missing pieces.

It quickly became evident that few of these well-built engines survived and finding parts would be difficult. The generosity within the old engine hobby for sharing information and the trust for providing original parts for re-casting was heart-warming. Over the next few years, original parts were generously shared by collectors, from which I cast and machined replacement pieces for my project including flywheel weights, the rocker arm and the rear crank casing.


Dempster engines are somewhat unusual in that the hit-and-miss timing assembly, igniter and magneto are located on the right side of the engine. The most challenging piece for this restoration was finding a correct magneto bracket, for which I only had a broken remnant stubbornly attached to the hopper. I found out that there were different brackets made over the years for this Dempster engine model and that the brackets are rarely found intact.

Finally, I found a collector who had a broken bracket piece that corresponded to the missing section of my bracket. The piece was purchased, and with the help of a local welding and machine shop a complete bracket was made. It took several rounds of trial and error to get the advance-retard timing lever mount correctly welded to the bracket. Rudy Adrian of Adrian’s Magneto Service, Lancaster, Minnesota, was immensely helpful, furnishing a complete copy of the original 12-page Dempster Mill Mfg. Co. Gasoline Engines Instruction Book and Repair List, a well-illustrated brochure for timing adjustments for old-style magnetos and igniters, and ultimately finding a correct and original Webster Tri-Polar Oscillator magneto in hot condition! Rudy was familiar with the “right hand” igniter and 180-degree rotated armature magneto for the Dempster and was able to beautifully restore the assembly over a period of several months. Overall, two years elapsed just in the restoration and fabrication of the magneto-igniter bracket and procurement and setup of the Webster magneto and igniter assembly!

Meanwhile, progress in freeing up the seized engine and photographing and cataloging parts gradually moved forward as time and budget allowed. When I finally was able to remove the head from the hopper, two cups of loose rust were found! At this point I took the heavily corroded engine core consisting of the hopper, seized flywheels and connecting rod assembly and base to a local bead-blasting shop to get everything to a clean cast surface to better soak and free the remaining stubborn engine parts.

Soaking the main and connecting rod bearings with Kroil followed by tapping with a ball peen hammer over several months finally released the seized bearings, allowing dismantlement and restoration of the flywheels and connecting rod assembly. The sliding governor collar broke during this, requiring machining of a replacement. With repeated heating, generous Kroil soaking and finally persuasion with a 2-ton hydraulic press in good friend Les Fossum’s shop, we finally released the captive piston with a loud “pop” from the badly corroded cylinder. I installed new cast iron rings on the carefully cleaned piston and took the engine block to Troy’s Engine & Mfg. in Rigby, Idaho, to machine and install a new cast iron sleeve. At the same time, new exhaust and intake valves, springs and keepers were made and the valve seats reground and mated.

During the same period, I designed and built a non-original – but correct for the period – handcart of laminated red oak for the Dempster, employing a set of vintage cast iron wheels I had previously found. Fellow collector Garry Anderson machined the axles and bearings for the antique wheels, at which point I completed the cart and pull handle.

The original fuel-air mixer had long been missing, but a generous Dempster collector provided a carefully dimensioned cross-section sketch from which Mark Moen, a colleague of mine, kindly machined a replica assembly to match the Dempster original! Rather than fabricating a new gas tank (the original was long gone), on eBay I purchased a nickel-plated 1950 Coleman lantern base and modified it for use as a replacement gas tank. It looks the part for the old engine!

Finishing touches

I was now at the point of priming and finish painting the engine parts for re-assembly. I had found from my research that the original Dempster engines were typically painted a dark “Brewster Green,” which is almost black. Instead, I chose to go with “Dempster Gray” as used on the original Dempster windmills to more distinctively highlight this unique engine (per C.H. Wendel, “Dempster Dumpster Gray” was referenced to DuPont 42677 or simply DuPont Gray 91992, which I was able to precisely match at Stan’s Paint in Idaho Falls, Idaho). Using original Dempster literature, Landmark Signs in Idaho Falls recreated the correct shop labels and engine tag to complement the engine restoration.

The Dempster engine uses two oilers – a typical piston oiler through the water hopper and a second, smaller oiler for the connecting rod bearing within the enclosed rear housing. The Dempster 1917 catalog specified a No. 1 Exploso oiler for the piston and No. 0 Emergency oiler for the crank. After several years searching for these elusive oilers, I picked up on eBay original No. 1 and No. 0 Lukenheimer oilers, which look like they belong on the engine, matching perfectly! The crank oiler requires a leather or bristle wick extension to brush and apply oil to the spinning connecting rod bearing. Essentially, the enclosed crank housing collects oil discharged from the piston, the rear crank oiler and oil for the timing gear, thereby acting as a splash oil pan for the moving parts at the rear of the engine.

I then assembled the refinished engine components from the base up on the newly built handcart, reassembling the newly restored engine piece by piece.

Finally, good friend and local engine collector Rick Thurmond provided invaluable help and expertise in adjusting the exhaust and ignition timing of the newly restored Dempster and we got it back smoking and popping in late September 2017. After five years – on and off – the Dempster restoration is more or less complete. I’m still looking for the correct slatted muffler and flat-belt flywheel pulley, but neither is essential at this point. Any help on these remaining items would be much appreciated!

The engine is a quiet, relatively steady runner, typical of a small hit-and-miss engine. I’m still getting accustomed to it, particularly the fuel mixer adjustment to keep it steady – but run times are smoothing out and steadily getting longer.

It’s always satisfying to see these old, long forgotten engines come back to life! My sincere thanks go out to all the generous people who helped and encouraged me along the way for this challenging restoration. This old engine came back to life and avoided the scrap yard! I just regret that Randy wasn’t here to see the culmination of this extended project – but perhaps he’s looking down now and smiling. Thanks, Randy, for the opportunity!

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