Sheppard Six-Cylinder Prototype Replica

R.H. Sheppard Company, of Hannover, Pennsylvania, began manufacturing diesel engines in 1937, carving out a small chunk of the diesel engine market. As with many engine manufacturers, they managed to expand considerably during World War II making a variety of products for the war effort. After the war, again like so many other manufacturers, Sheppard struggled to find a place in the post war marketplace.

Their first idea was diesel repower kits for farm tractors and Sheppard briefly offered a kit for the popular International Harvester Farmall M. At the same time they began developing a line of tractors. The repower kits and the first of their tractors debuted in 1949 at about the same time. The overpriced and largely redundant repower kit soon faded away but the tractors continued. During various parts of 1949, Sheppard debuted three tractors, the single-cylinder SD-1, the two-cylinder SD-2 and the three-cylinder SD-3. The SD-1 would be short-lived, 1949 only, and the line would be joined by the SD-4 (yep, a four-banger) in 1954.

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Failing Finals and Big Tractor Dreaming

Sheppard built their engines and produced many castings in house but they bought the tractor final drive for the SD-2 and SD-3 from Timken-Detroit. It was largely the same unit being used by Cockshutt and other smaller tractor manufacturers. Those Timkens would play a part in the evolution of the Sheppard tractor.

The business end shows basic tractor… swinging drawbar, PTO and little else. Hydraulic remotes were an option but Sheppards never got three point hitches.

At some point around 1950, failures began occurring with the Timken final drives, most often in the SD-3. The specific failure area was at the ring and pinion interface. Under heavy load, the ring gear and carrier was deflecting just a little and under the right circumstances, teeth would be stripped on the ring or pinion. It was a very simple fix to add a load bolt limiting the deflection to 0.010-inch. Adding the load bolt also became a service fix but it seems clear the company had doubts about this final drive being able to support tractors with more powerful engines. And by all reports, Sheppard had power upgrades on their minds.

From here the history, timing and motivation are not all that well documented. It’s known Sheppard was planning a four-cylinder version of their basic engine design, with a projected output of about 50 horsepower and it’s likely it would find a home in a tractor. We also have reports that they were considering a six-cylinder powered tractor.

The Model 12 engine was offered for a number of applications, including marine, generator, power unit (shown) and as an automotive engine. It came in two bore sizes 4-inch and 4.25-inch. The larger bore was denoted by a particular suffix, either D (for power unit or generator) or E for the automotive unit. The bigger bore unit (larger bore wet sleeves) made six more horsepower. As a power unit, the Model 12 weighed in at a hefty 2,100 pounds. Bare in automotive form, it was just shy of 1,800 pounds. It’s known that one Model 12 engine was installed into a Mack truck the factory used to deliver parts and tractors.

After the final drive problem was discovered and largely corrected, it highlighted a need to evaluate the Timken against future power upgrades. It was a simple answer to install an existing Sheppard Model 12 six was into an SD-3 and see what was what. The three-cylinder Model 6 engine made 32 continuous flywheel horsepower at 1650 rpm. The Model 12 made 60 horses at the same rpm and more if spun up to 1800 or 2000 rpm. If there was a final drive issue, yeah, that would uncover it.

It seems clear putting the six in front of the Timken convinced them to start development on a stronger in-house built final drive. This 10-speed unit (5×2) would be complete late in 1953, just in time to debut in the new four-cylinder powered SD-4 tractor. People who worked at Sheppard at the time, including Richard Eastham the owner of the SD-6 replica featured here, have said a six-cylinder was going to be the next step. Fate and changing times would prevent that from happening.

The six-cylinder test tractor had two-year working life at the Hanover Canning Company, presumably working in their nearby crop production areas. Richard Eastham is the very guy that brought the tractor back to Sheppard, where it was dismantled.

Coulda Been a Contenda!

The SD-4 was a big step into a higher powered realm of diesel ag tractors and an SD-6 would have been a huge step. By the time the SD-4 appeared, the ag side of the company was lagging. Sheppard tractors were generally good machines in their era and farmers liked them. They lacked some of the refinement found in other makes, but the SD-4 was evidence they were working towards correcting that. The biggest problem with Sheppard was not with the tractors but with the dealer agreements. The company didn’t make it easy or attractive to become a dealer versus the other manufacturers so they just didn’t get around all that much. Over almost seven years of production, only around 1,600 Sheppard tractors were sold and just 177 of those were SD-4s.

The Model 12 six debuted right after World War II and was a development of the Model 6 three cylinder engines. All the Sheppard engines were “modular” in the sense that they shared a common bore and stroke and most internal parts. The 4-inch bore Model 12 delivered 280 lbs-ft of peak torque from 1000-1200 rpm and the 4.25-inch bore engine did 325 at the same rpm. The automotive 4-inch bore engines could crank out up to 90 horses at 2000 and the 4.25-inch made 100 horses. The continuous ratings, which a tractor would use, were much lower… 61 and 67 horses at 1800 for the two bore sizes.

A powerful 60-plus horsepower, six-cylinder diesel tractor in the mid-fifties could have changed the tractor landscape but by then, Sheppard had discovered it’s true destiny. They had invented a power steering system for the SD-4 and it turned out to have applications in other areas… trucks, tractors and more. Soon, steering systems became the focus. Tractor production stopped after 1956 and diesel engines faded in the 1960s. R.H. Sheppard Company remains in business to this day still building steering systems.

Be sure to see the second part of this Sheppard Two-Fer in the Vintage Smoke column.

Well, it’s not the lap of luxury, unless you’re a masochist, but it was typical of the time. Farming in the early ‘50s… steel tractors and iron butts!

The Sheppard diesels were indirect injected, with a prechamber built into the cylinder head. The injection system has been touted by history as being “farmer repairable.” While it is a simple (and imprecise) system, we kinda doubt Sheppard wanted any Farmer John digging into his injection pump.

Richard Eastham’s SD-6 replica is a showstopper. The six-cylinder SD is legendary among Sheppard collectors and at least three replicas have appeared. This one was built by Richard Eastham, the only guy left who can claim to have actually driven the original one. It’s largely as he remembers it when he worked at Sheppard. One divergence is the addition of a hood, which the original test unit didn’t have. Eastham’s was built on an SD-3 Timken final drive as the original was. The other SD-6 replicas, one built by John Camden and the other by John Hershey, both use SD-4 powertrains. These SD-4 based units represent what the SD-6 might have been had it actually gone into production. Richard says the conversion was relatively simple. He added a longer frame rail to accommodate the longer engine and extended a few lines and the steering linkage. The six added about 600 pounds to the tractor.

SPECIFIATIONS

1950 Sheppard SD-6 Replica

Engine: 6-cyl. diesel, Sheppard Model 12
Displacement: 377 ci
Bore & Stroke: 4 x 5 in.
Flywheel Power: 60 hp @ 1650 rpm
Compression Ratio: 22:1
Transmission: 8-speed (4×2)
Weight: 5,300 lbs
Fuel Capacity: 15 gal.
Tires: Front – 6.00-16
Rear – 11 x 38