Restoring a 1903 5 HP Samson Gas Engine

5 HP Samson engine

Lester Bowman's 1903 5 HP Samson Model N.

Photo by Lester Bowman

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1903 5 HP Samson Model N
Manufacturer:
Samson Iron Works, Stockton, Calif.
Model: Model N
Year: Circa 1903
HP: 5
RPM: 300
Serial number: unknown
Bore: 5-1/2-inch
Stroke: 10-inch
Flywheel diameter: 36 inches
Governor: Flyball, volume governed
Ignition: Low-tension
Cooling: Tank

Samson engines have always intrigued me, and I've always wanted an early Model N. Fortunately, a good friend helped me to acquire a circa-1903 5 HP 'web spoke,' so named by Samson collectors for the inboard counterweight cast into one of the 36-inch flywheels. Designed by John M. Kroyer, this Samson is a long-stroke (5-1/2-by-10-inch bore and stroke with a 2-inch-diameter crankshaft), slow-speed, volume-governed gas engine equipped with Samson's later-style one-piece igniter.

The past owner started restoration but, unfortunately, died before he could finish it. When I bought the Samson in 1998, it was set up on a cart with a cooling tank. Another good friend hauled it to my home in Modesto, Calif., and before I worked on it all 1 could do was sit and admire it for several days.

Samson engines are beautifully proportioned with large flywheels and turned connecting rods that are fitted with heavy brasses. Both valves - as well as the igniter - are mounted in the pre-combustion chamber. The governor is belt-driven using a balanced valve while a peculiar valve link controls the four-cycle events. All Samsons are tank-cooled, throttled-governed engines using poured babbitt for the mains and low-tension ignition.

If it's not one thing, it's another
Once the initial thrill of acquiring the Samson had passed, I began checking it over. For starters, the timing was so far advanced it wanted to take the skin off my hands even on retard. I reset the ignition and tried again, but it would only run for a little while and then die. But if I waited a few minutes, it would start right up again. While dealing with this problem, I learned a very important lesson. Studying the points under a magnifying glass, I noticed they were 'brassy' looking. Further inspection revealed someone had built the points up with brass brazing rod. I made new points to correct the problem and reassembled the Samson. I now had excellent spark, but the engine turned over too stiff. Checking into it, I found the main bearings were tight so I shimmed them as needed.

Now I had the Samson running, but the governor spindle shaft kept binding in the valve body. It turned out the shaft was bent and I ended up making a new one because I couldn't straighten the original to my satisfaction. Now the Samson governed properly, but the igniter trip rod kept sticking, causing the engine to die. I repaired that problem as well as the flooding mixer, which had a rotted-off fuel needle valve. Finally, the engine ran very well, never missing a lick.

Accidents happen
The Samson engine had suffered an accident at one time, which was the hardest problem to overcome. Somehow, about 30 percent of the large cam gear's teeth had been fractured off, leaving only about a third to a half of the teeth remaining. I was afraid to run the Samson very much in this condition, especially since I could envision another tooth breaking off causing irreparable damage. I even considered letting someone else have the problem as it seemed beyond my abilities and resources to repair or find a good replacement cam gear.

I thought about the problem for a few years, and I even discovered what had caused the breakage. Apparently, a piece of heavy wire got tangled into the gear mesh, wrapping itself around the large cam gear, causing teeth to fracture and in the process bent the timing gear pin. The gear on the crankshaft suffered no apparent damage since it was made of steel, which is harder than the cast iron cam gear.

I took the original cam gear to a shop specializing in gear work in Stockton, Calif., about a mile from where the original Samson foundry was located. The teeth on the gear have an odd angle and a standard gear blank couldn't be found that duplicated the correct profile. Because of this, I was forced to have a new gear machined from solid steel, which as you can imagine cost me a princely sum. I told the gear shop to leave the bore diameter alone as I would machine it later to fit.

To fit the new cam gear I made a tapered mandrel that fit the inside diameter of the old cam gear tight enough to keep the gear from turning. Mounted between centers on a lathe, I very carefully turned off the old teeth until the cam was small enough to accept the 'ring gear' I envisioned in my mind. Then, I made a fixture to hold the newly machined blank gear and bored it out leaving a 0.006-inch shrink fit. Heating the 'ring gear' with a torch expanded it, and making sure I had my marks lined up 1 dropped the old cam gear (with no teeth) into the 'ring gear.' It cooled down and voila! I had a beautiful new set of teeth on the original assembly. I had preserved the original integrity of the cam gear while doing a first class repair job. Next, I installed a small set screw to lock the ring gear in place just in case it needed a little more re-enforcement. The finished repair done to this cam gear is nearly invisible to the naked eye, and the original patina is still inherent on the assembly.

Trading one problem for another
With everything assembled, the gears made a grinding noise! Oh boy! Finally, 1 found the time to pull off the flywheel and small crank gear, and I was forced to return to the specialty gear house. 1 paid yet another princely sum to have the crank gear made - but it was worth it. When I assembled everything, I was worried the Samson might have a problem with misalignment. Those fears proved unfounded since the Samson now runs beautifully with only a faint whisper of mesh. I'm very proud of my work on the gear train.

I run this engine on propane and have run the rpm as low as 60 using a demand regulator and air/gas mixing valves. The large flywheels really let this engine run slow.

No nameplate is present on this Samson, and there's no indication it ever had one. The cylinder shows little 'dimples' where the plate holes should be drilled. The holes are spaced to fit the large early plate, and I believe the cylinder may have been replaced at one time due to wear or frost damage. I also believe the late-style pre-combustion chamber and one-piece igniter were fitted at this time. 'X33' is stamped on the governor pieces, and '6' is stamped on the end of the crankshaft, rod and brasses. I believe this number means these parts would also fit a 6 HP engine.

The Samson's history
Through a unique series of events, I discovered this Samson was originally used on the Osterman Ranch north of Clements, Calif. The fellow who salvaged it told me the Osterman Ranch is now under Camanche Lake, which now covers the whole area. My Samson engine evidently pumped water out of the old Mokelumne River. Despite the unavoidable and numerous headaches incurred while restoring my 5 HP Samson engine, I feel very rewarded and satisfied. After going through an extensive restoration like this, I can share one shred of wisdom: Every month I read about the wonderful engines in Gas Engine Magazine that require hours of machine work and about guys who build seemingly impossible parts, but I just want all you guys who don't have machine shops or expertise to know it's possible to do first-rate repair with limited facilities. Don't get discouraged - I didn't, and now I have a great-running Samson engine.