1/3-Scale Model Pacific Vapor Engine

Modeler's Corner

pacific 1

Lester Bowman made this 1/3-scale Pacific vapor engine after seeing photographs of Anton Affentranger’s full-sized example in Stan Grayson’s book Beautiful Engines.

Photo by Lester Bowman

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My copy of Stan Grayson’s Beautiful Engines is no coffee table book. It is dog eared, dirty and very well read. On page 41 is Anton Affentranger’s beautiful 2 HP Pacific. These lovely photographs inspired me to duplicate the Pacific in miniature.

As I thought about the project, I happened to remark to master model craftsmen Roland Morrison, “Wouldn’t it be nice to build a Pacific?” I quickly found out that a guy needs to be very careful what he says to Roland because a few days later, a large envelope arrived with copies of the original Pacific build prints. Roland also included his own thoughts and sketches on how to best approach the building of the model. He said he felt the world was ready for a little Pacific. We had a vision.

Background on the Pacific
Only a handful of Pacific vapor engines have survived. Stan has written extensively on patents assigned to Pacific from Daniel Regan and the litigation which ultimately led to the Union Gas Engine Company.

Pacific vapor engines have a gearless 4-stroke design using a unique “crossover” cam. The crossover cam provided the 4-stroke cycle, and a secondary lift cam attached to its face opened the exhaust valve. Speed is controlled either by hit-and-miss or a centrifugal flyball governor and wedge setup to control the intake valve opening. I don’t think the marine engines used governors but I’m not sure.

Ignition is low tension using an insulated “finger” protruding from the center of the piston head. There are two insulated spring steel blades with points situated within the cylinder itself. When the piston approaches top dead center (TDC), the finger compresses the two blades together completing the electrical circuit. As it rolls over TDC, the points separate causing a spark and ignition. A spark saver is incorporated into the circuit as well, working off the swing arm.

Very simple in theory but mechanically complicated, the valve operating gear was prone to rapid wear. These engines were difficult for new owners to understand, but when set up right they run well. It’s fascinating to watch the cams do their magic.

Making the model
What happens in the process of making a scale model is that you scale all of the full-size pieces and translate them into wood patterns. Then you add shrink and machining allowances and perhaps a chucking piece. By the time the little patterns come along, it is hard to tell if anything will fit.

I suppose I spent more time on the patterns than on actual machining. The thin beading around the crankcase openings can be duplicated on the pattern using solid core solder planed to half its thickness with a sharp block plane. I shaped it then attached it with quick-set epoxy. The patterns were then shellacked and smoothed with fine steel wool.

The crankshaft was turned from solid stock between centers. My little 7-inch AMMCO shaper was used to machine the main bearing flats within the crankcase using extended cutters. The main cap holes were also drilled from within using a special tool I designed.

I babbitted and line bored the main bearings with shims in place using my lathe. Oil grooves were cut with a Dremel and burr.

The cylinder has a cast iron sleeve bored and honed. The cylinder head is also water cooled, using shrink fits to make the jacket.

Troubleshooting as you go
I tried to replicate every part as closely as possible to the full-scale appearance, but some changes were required to build a safe and practical engine. The crankshaft diameter was increased for strength, which affected the crankcase clearance for the big end on the rod. Changes on the big end affected the stroke, and so it goes. I spent many a night slumped over the drawings making sure the parts would fit.

The crossover cam was a challenge. Before I built the Pacific, I made the machine to cut the cams. In the end, I had seven useless face-cam dies, but the eighth cut a cam that worked with some file work. Success? I don’t know – you tell me.

It’s wonderful to see all of the big castings machined and assembled. The small parts come next and this is tedious work. Do a little here then a little there; fit this shim to that; too loose then too tight; binds here, then there and so it goes. I wondered at times if the little pieces would work at all in the valve actuating mechanism. I was surprised and very pleased that everything came together with no changes to the basic patterns. It all worked exactly like the original and I felt a great sense of accomplishment. It felt like the Pacific was giving back to me.

Future plans for the Pacific
I have a few things left to do such as making a cooling system and surface carburetor. The little Pacific engine suffers from the same drawbacks as the full-size ones, mainly retarded ignition timing. The nature of its make-and-break ignition allows the spark to occur only after TDC. In a model, this characteristic is amplified. The engine runs but needs to hit several times before it “comes up on the governor.”

The engine has a fully operational low-tension ignition system incorporated into its design. However, after much experimentation with the low-tension system with varying degrees of success, I installed one of Roland’s Rimfire spark plugs and used a high-tension coil for ignition. This did the trick! Performance greatly improved and the engine comes up on the governor like it should. All of this testing has been done on propane fuel using a model SD demand regulator. I am going to build a small gasoline carburetor and see if this helps the running characteristics. If so, then I will go back to the original make-and-break ignition and see if that changes anything.

Some of the items I couldn’t make myself included  the lovely little bronze clean-out plates mounted on each side of the cylinder. They are embossed with “Pacific Gas Engine Company, S.F. CAL.” Roland Morrison and Marvin Hedberg partnered together to create the beautiful plates using somewhat more modern techniques than I would have used. You need to check out their website at www.morrisonandmarvin.com. They have the highest quality scale model engine castings available anywhere in the world. I’ll also add they are two of the nicest and most knowledgeable guys you’ll ever meet. The lovely plates are just one of the many contributions they made to the Pacific, adding immeasurably to its form and beauty.

Appreciating the craft
A lot of small engine work is spent building different fixtures to hold various parts for machining. Serious thought is involved in trying to determine how the old timers did it. I made it a point to use the same type of machine tools to build the parts that would have been used in 1889.

Most of the time, the work is hard and dirty but there are crystal clear moments when one can see into those old machine shops and almost hear the voices of the great men who pioneered the early California-built engines. There are moments when the same sense of accomplishment is felt along with a heightened appreciation of the astonishing work done by the early builders. There is a tremendous reward in building these engines with old techniques and doing things by hand. It is the gift of building scale engines.

Every craftsmen has their own way of doing things and, generally speaking, the end result is the same. One man cuts a keyway with a CNC mill, programming the computer, loading the vice and pressing a button. The mill does the rest. Another man takes his hammer and a bag of chisels and cuts the same keyway. It takes much longer and requires greater skill, but which man better appreciates the end result? The journey to this end result is where the difference lays and determines what we learn from the result. The journey teaches us the stories behind these small engines and reveals their great significance during the unfolding of the machine age.

Contact Lester Bowman at 175 N. Santa Ana Ave., Modesto, CA 95354 • (209) 527-4665 •  samsonironwks2003@yahoo.com