KISS -- Keep It Simple (add your own second "s")...
My previous post gave a brief history of the early 2-stoke marine engines. Stan Grayson, who wrote "Old Marine Engines: The World of the One-Lunger," noted that even though they were relatively expensive, they were quickly accepted among the working watermen because they provided a competitive advantage -- and were useful when the wind and the current did not cooperate. And they were simple -- to operate and to maintain.
Before there were reliable spark plugs, and even after, there were alternate ways to ignite a compressed charge of gasoline or kerosene. Of course, Rudolf Diesel had developed his sparkless engine -- which depended on high compression pressure (at least a 15:1 compression ratio) to generate the temperature required to ignite the vaporized fuel (his first patents were granted in 1892; the first diesel engine ran in 1897). But the easy-to-build and easy-to-maintain 2-stroke engines in the early 1900s were not high compression engines -- the development of non-leaking seals and strong materials is a science as well as an art (and living with leaky shaft seals is quite acceptable to most boatmen, even today). The early 2-stroke engines utilized the relatively low-pressure piston and seal technology and were designed to produce moderate compression ratios, in the range of 3:1 (easy to crank over) to 6:1 (very tight). In fact, Grayson notes that it was possible to replace a blown head gasket with material at hand while out on the water. Not the best situation, for sure, but possible. The early engines tended to be overbuilt, with steel pistons and extra metal in the castings, which most certainly reduced the number of manufacturing rejects. Weight was a factor, but not a limiter, and some of the engine builders did not even bother to quote weight. And the extra iron certainly helped if the cooling pump was beginning to limp a bit.
Compression ratios -- Old Marine Engine discussion board: www.oldmarineengine.com/discus/messages/3430/7949.html
With lower-compression engines there was plenty of space for a charge deflector -- sometimes just a piece of angle iron bolted to the top of the piston -- to enhance exhaust evacuation. And there was room for the spark source, even with a simple flat head. The old marine 2-stroke engines basically used one of two ignition sources: "make-and-break" igniters; or spark plugs. Both had their advantages and disadvantages and Grayson breaks it down as "low tension" (that is, low voltage) versus "high tension." The former is a mechanical "sparker" solution, perfect for a simple engine. Here's a nice video of a make-and-break Acadia Atlantic running along. Try slowing the video down so you can see the operation of the mechanical mechanism at the top of the cylinder that is driven by an eccentric near the flywheel. Seems like a pretty complicated mechanism to me. But...it would also seem to be relatively easy to repair or adjust with a couple of basic tools, and without a lot of high-tech training. And since it operates at low voltage (like around 6 volts), it can get liberally doused with seawater -- and still work; the parts that actually spark are all inside the cylinder. Corrosion of the connections -- easily observed and remedied -- were the biggest electrical issue, once the mechanical contraption was adjusted correctly. But since the igniter is a mechanism with lots of bits and springs, how long will it work before it needs additional adjustment; or before something breaks?
For those of us who grew up with points and plugs, it's not immediately obvious how exactly this make-and-break ignition system works. Here is one description, dated 1906, by K.K. Williams, E.E.
"Without the aid of a coil, no spark can be produced that is large enough to ignite the gas when using batteries to generate the current for either [make-and-break or jump-spark] system. The make-and break coil consists of one continuous winding of coarse insulated wire wound over a soft-iron core. When the electricity passes through the coil, and the circuit is suddenly broken — that is if two wires are separated after being connected — a spark of high intensity follows the break or gap for a very short period of time. To produce the spark in the cylinder a mechanical motion is imparted to one electrode or end of the wire as it might be, at the proper point in the revolution. The moving electrode touches the stationary point, to permit the current to flow, forming a circuit, just before it is broken.
The important point here is that the actual make-and-break igniter, shown below, is a pretty simple mechanical device that bolts onto the top of the cylinder. AND, it has to open quickly to create the "spark", actually the arc across an interrupted electrical circuit. As you can see on the igniter below, the part with the springs (on the outside) rotates to strike a stationary "anvil" inside the cylinder (kind of reminds you of an old flintlock rifle striker mechanism). On this igniter, it looks like the stationary "hot" electrode is electrically insulated from the base so that the rotating hammer is a simple close-clearance sleeve.
"Make-and-break spark as ordinarily utilized requires a large voltage as generally compared with jump-spark, and uses more at each time of ignition or contact, because the contact is made during a certain length of the revolution. This makes the make-and-break system stem utilize a larger amount of battery power per hour than the jump-spark, as will be explained further on in this article.
"The spark generated by using the make-and-break system is. however, larger and hotter than the jump-spark. Properly designed, an advancing arrangement can be made to advance and retard the spark through the same useful portion of the revolution as jump-spark, but very few designers seem to care to arrange this important feature of the make-and-break system, being satisfied to set the spark at one point in the cycle, and generally not being able to change unless the engine is stopped. The hammer type of make-and-break has given very good service. The power to be derived from a gas engine is proportionate to the proper combustion of the gases.
"Make-and-break gives the hotter spark [and] consequently more power [than jump-spark] because it ignites the gas more quickly. It gives a very instantaneous ignition and less advance is required. because the action is quicker than jump-spark. Then again, this system has only one circuit and is easily understood by the novice and appeals very readily to the beginner."Make-and-break advantages are: it's simplicity, using one circuit; a test of the battery circuit is a test of the sparking circuit; ignites the gas quickly and thoroughly; low voltage circuit; not readily effected by spray or rain; and coil not easily burned out. Its disadvantages are: working parts in the cylinder firing chamber; loss of compression sooner or later through the movable electrodes bearing; inaccessible generally, although not always, to advancing the spark; requires setting regularly; sparking points wear; springs cams, levers rods; and requires an unnecessary amount of battery current. The claim of unnecessary amount of battery is better explained in considering that ten times more current -- or the time of ignition is ten times longer -- at 100 rpm than at 1,000 rpm, with a waste of 9/10th of the battery power at the former speed.
While it's not a marine engine, here are a couple of great videos of the innards of a 1908 Matheson automotive engine that has a make-and-break ignition, www.youtube.com/watch?v=egbCVxAKvX0. The second video shows the same engine "sparking" -- the sparks look pretty "fat." This ought to convince you that, once all the adjustments are right, the make-and-break ignition works very well, www.youtube.com/watch?v=KZyuCpoXYgU
In contrast to the mechanical, low-voltage make-and-break ignition discussed above, jump-spark engines use spark plugs and points. And they require step-up coils to generate high-voltage sparks. They are what we grew up with in our cars. Williams continues...
"Comparing the two systems. jump-spark advantages are its accessibility to advancing and retarding; consumes less electricity; the strength of the battery can be determined by the vibrator's action; requires no engine apparatus such as rods, cams, springs, levers; the plug screws into the cylinder leaving no possible means for loss of compression to be traced to this source; and jump-spark ignites the gas more readily in starting because the points are so small that heat enough is generated to warm the gas at the flame.
"The disadvantages are: leaks in secondary or high tension circuit; cracked or fouled plugs; a positive current in the primary circuit is no guarantee of a spark occurring at the plug points; liability of burning out the secondary winding if too many batteries are in circuit; lags slightly at high speed requiring a further advance than make-and-break; spark-plugs carbonize; is affected by dampness or moisture, such as rain or spray; and extreme high compression blows out or insulates the spark.
K.K. Williams, E.E., "Make-and-break versus Jump-spark", Powerboat News, Volume 2, No. 4 (August 26, 1906), www.oldmarineengine.com/technical/MBvsJS.htm
John Davis' video of his Detroit Engine Works motor is a great demonstration of a 2-stroke spark engine and how it operates. Notice how he can use the advance lever to easily reverse the rotation -- no gearbox needed. KISS.
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If you are still curious about make-and-break ignitions, here are some more resources that you can check out:
"Internal Combustion Engines and Tractors, Their Development, Design, Construction, Function and Maintenance," notes of a series of lectures, delivered by Oliver B. Zimmerman of the Engineering Staff, International Harvester Company, Chicago, 1920.
www.gasenginemagazine.com/gas-engines/function-ignition-apparatuses-engine-systems/
www.gasenginemagazine.com/gas-engines/function-ignition-apparatuses-engine-systems/
A more contemporary EEs take on the old engine ignitions and how they operate, see David Cave's article in Gas Engine Magazine (Sept 8, 2000)
Hooking up a make-and-break motor, www.youtube.com/watch?v=yWINn34ixPQ
In addition to Stan Grayson's book and whatever information I could find via Google, I have used photos of old motors from several messabouts and museums around the Chesapeake Bay. I need to give a shout out to the Upper Bay Museum in North East, MD, which has a nice display of early small marine motors, both outboards and inboards. Finally, the absolute best place (in my opinion) to see restored and working old marine motors is at the Calvert Marine Museum (Solomons, MD) Maritime Festival that is scheduled for May 1, 2021. Collectors come from across the country, but it's still a very accessible and low-key gathering, and much easier to get to (and less expensive) than the show in Mystic Seaport, CT. And the best place to research the old 2- and 4-cycle engines is the Old Marine Engine discussion forum.
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