1927 CUMMINS MODEL P
When 1927 rolled in, the Cummins Engine Company was in it’s eighth year of operation. Founding engineer Clessie Cummins had started in 1919 with a small shop in W.G. Irwin’s garage and a license to build oil engines using the Hvid (pronounced “Veed”) system. That engine, and a disastrous association building them for Sears, Roebuck & Company, almost put Cummins out of business. Clessie engineered his way out of the crisis with innovative new engine designs that began appearing in 1924, and the Cummins Engine Company started on the road to success.
The new era started off slowly but a big boost came in 1925, when Northwest Engineering Company, of Green Bay, Wisconsin, inquired about diesel engines for it’s line of power shovels (we call ‘em excavators today). The Cummins Model F was still fresh off the drawing board and had been well proven as a stationary and marine engine, with one through six-cylinder variants. As part of the agreement with Northwest, Cummins also developed an enlarged variant, the Model N, which followed the same basic design of the F but the bore and stroke was enlarged from 5.5 x 7.5 to 5.75 x 8.5 inches.
Government, particularly the Bureau of Lighthouses, as a fuel-sipping stationary electrical powerplant but the reputation it acquired in Northwest power shovels was at the opposite end of the spectrum. The laundry list of problems in that applications was extensive. The exposed camshaft and rocker gear did not do well in the extremely dirty environment where power shovels were found and reliability became a big issue.
The dirty environment extended to the fuel as well. Clogged injector nozzles was a common industry problem due to inadequate filtering, poorly refined fuel and carbon buildup. On top of that, the injection system of the F, which worked very well in stationary and marine applications, was ill-suited to the operational environment of a power shovel, which varied from a massive load that badly lugged the engine, to running at peak rpms with little load. The injection system didn’t have the flexibility necessary and tended to overfuel during those heavily loaded periods, causing further durability issues.
These problems had solutions and Cummins instituted several right away. Among the first was an air chamber device, technically known as the cup wiper but is better known as the “sneezer.” It was a small chamber in the piston that stored some of the compression pressure and when cylinder pressure dropped after the firing event, that stored pressure blasted fuel droplets off the injector tip so they wouldn’t make deposits. The sneezer carried on in other Cummins engines into the Model H-Lines.
To solve the worst parts of the valvetrain wear issue, the Models P and W debuted. They shared the bore and stroke dimensions of the Models F and N, as well as the per-cylinder power outputs, but they featured an enclosed, one-piece crankcase that housed the camshaft and lifters. The rocker gear was still exposed. The P and W engines came only as four-cylinder inlines, versus the multi-section blocks of the F and N that could be built with one to six cylinders. Cummins also introduced a new injection system for the P and W with better metering capability, which is detailed farther along.
By the time most of the upgrades had happened, both sides were disillusioned and disappointed with each other. Northwest and Cummins didn’t renew their contract and parted ways in 1927. Clessie was later said to have learned a lot about applications from the experience and the company spent more time matching engines to environments rather than simply making sales. These lessons bore full fruit when the fully enclosed Model U debuted in 1928, along with the legendary Cummins single disc injection pump.
The four-cylinder Model P was rated at between 50 and 60 horsepower at 600-700 rpm, producing about 420 lbs-ft at those speeds. According to Cummins historians, only 24 model P engines were built. About half of those went to Northwest before the contract expired and the rest were sold into stationary and marine applications. Cummins historians recently made a count in the records and determined approximately 491 Models F, N, P and W engines built to 1931 before they were completely phased out after being outclassed by the Model U. The legendary Model H (see Diesel World April and May 2019 issues) came just a few years later and eclipsed all of them, soon putting the Cummins Engine Company into full profitability.DW