Gas Engine Magazine

Good Technology Never Dies

By Staff

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

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

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

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

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.

  • Published on Oct 1, 1997
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