5523 So. Peach Fresno, California 93725
Fuel check valve open, plunger moving up, fuel enters plunger chamber being heated in annular fuel space 'A' 180°.
Plunger fully retracted, correct amount of fuel deposited in plunger chamber. Hot air being forced thru fuel charge. Next charge being heated in annular space 180°.
Injector plunger moving down injecting fuel into combustion chamber until seating against inner cup. Injection begins about 25 ° before top center, finishes about 10° after top center. Next fuel charge still being heated in annular space180°.
Plunger seated against inner cup. Fuel being heated in annular space180°.
Illustration No. 1
How many engine designs can you think of made 70 years ago that are still in use today? Well, I can only think of one, and it's in many trucks that pass you on the Interstate. It was designed by Clessie Cummins. It is known as the Cummins Diesel Cycle. The idea was conceived in 1927 and put to use in 1928. Take a look at Illustration No. 1. I am sure all of you have used an air tool at one time. As you use the tool, it becomes cold as the compressed air is released. Just the opposite happens when air is compressed. It gets hot. That is why your compressor has cooling fins. Now, Cummins fuel injectors go through four cycles. What a lot of people do not know is that air is injected into the injector on its second cycle. This happens on the piston's compression stroke.
The compressed air is forced into the injector heating the fuel causing it to convert into a gaseous state. Then when the injector plunger moves down, the mixture is injected into the combustion chamber and we have ignition.
The above information, illustration, and further illustrations were taken from a 1931 Cummins Engine owner's manual. The following statistics came from a Cummins newsletter titled 'The Way We Were.'
Cummins built about 600 engines from 1924 through 1931 consisting of six models: F, N, P, W, U and K. Serial numbers 8000 to 8600. Engines built in this time period are considered rare today.
What I have restored here is a 1928 year, Model U, serial number 8266. It is rated at 16 HP @ 800 rpm and is a 2 cylinder 4 stroke diesel. See test record.
U's were produced in 1, 2, 4 and 6 cylinder configurations. They operated on the Cummins Diesel Cycle and look very much like today's engines on the inside.
I found this particular engine at an auction in Los Angeles. It had been used at a silver mine in Silver Pines, California. It may have been used to pump water or run a compressor. It is a marine style engine equipped with an over center clutch pack and brake. Inside the clutch pack are three planetary gears which increase the output speed three times the engine rpm. They also cause it to change direction from right hand to left hand rotation. This clutch gear box combination was made by Snow-Petrelli Manufacturing and was called 'Joe's Gears.'
The engine must have been used at a high altitude since it had a lot of water freezing damage. At the lower elevation it does not usually get cold enough to do damage here in California. Most of the damage was done to the cylinder heads and fuel pump. These items were each put into a forge, heated cherry red and welded with cast iron welding rod. A torch and welding tip were used, not nickel rod. Welding rod made out of cast iron. The engine must have been very dependable because every moving part was worn out. It was very well used! I spent over 600 hours machining bushings, shafts, roller, bearings, you name it. Some parts were a real challenge. The only parts available from Cummins were the injector tips and the cam rollers which are the same as the small cam 855 cubic inch series engines. The flange and hole centers on the crankshaft ends of the U are the same also. This hole pattern is considered standard on most Cummins engines. The connecting rods are very similar to the 855 cubic inch engines. Same length and width, but with Babbitt bearings.
The fuel pump is a work of art (see Illustration No. 2, and Picture 1). It has two cam operated plungers with fuel delivery metering achieved with adjustable centric. The fuel pump took me a day to put together and a day to get it adjusted right. The engine timing is achieved through cam roller activated injectors. The cam rollers or follower are adjustable (see Picture 2). They are moved in or out in relation to the cam lobes. The timing is adjusted by changing the gasket thickness on the box. Dial indicators are used to do this. The same tool used on today's engines fits perfectly in this 69-year-old Cummins (see Picture 3). The injector timing was set at .030 of an inch of travel when the piston was at .2032 of an inch before top dead center.
The pistons have four compression rings and one oil ring. They are also equipped with sneezers or cup wipers. A second explosion occurs during combustion in a small cup within the piston and is blown through a small orifice directly at the injector cleaning the tip (see Illustration No. 3).
The water pump is solid brass with a built-in flow regulator. The block and radiator hold about 30 gallons of water.
All pictures on this page are of Floyd Schmall's now restored Cummins engine.
The cylinder heads are cooled with water cooling nozzles that are set in the block (see Picture 4). They concentrate the water flow toward the center. The only problem was the cooling water did not completely drain out of the heads. This became a problem in cold weather. The exhaust manifold is also water cooled. The governor works off of centrifugal force and is hooked up to the fuel pump with linkage. The oil pump is huge. It measures out to be about a 10 gallon per minute pump. The oil pan holds five gallons (see Picture 5). I found casting stars in the block. They were used to clean the castings out. All the castings were coated with paint or sealer at the factory.
This engine was originally equipped with a 32 volt Leece Neville starter generator combination. It was chain drive and mounted above the clutch housing. I have not been able to locate one of these. Perhaps you can help? I would also like to find an extra cylinder head and more literature. I am using a 12 volt starter now.
Does anyone know Mr. Johnson?
The original color for Cummins marine engines was a sea green. Though the engine looks blue it is actually turquoise. I matched the original paint to Peacock Green Dupont #49618A acrylic enamel.
There is nothing like the first start up after a long restoration. After priming the fuel pump it took right off. The old Cummins sounds like a John Deere diesel.
In 1931 Clessie Cummins put a four cylinder version of a 'U' in a race car entered at Daytona Beach on Memorial Day. Two months later he put a 'U' in a truck and the rest is history.
I would like to thank the following people for help, parts, information and interest in this project. Bryce Morris, Ralph Richie, Leroy Trytton, Frank Silva, Tim Crabtree, Jim Rogers, Margot Green, Glenn Karch and Lyle Cummins.
Lyle is writing a new book about his father and the Cummins Engine Company. He has tons of new information. As with most companys' history, they have very colorful beginnings. Cummins is probably the most fascinating of them all. Look for the book here in GEM.