Obsolete Outboards
by Max Wawrzyniak

Big Twins
We get letters. (Actually, we get e-mails)


Thanks for taking the time to read this email.

I was startng to build one of the AF4G's but the engine pricing was getting a bit out of hand. A used 25hp honda 4 stroke with remote control/electric start is about $3000.00 if not more. A 25hp yamaha with remote everthing is about $2600.00. This was pretty discouraging.

Of the typical boat/motor/trailer rig, the outboard motor is usually the most expensive component. This is how the marketers of fishing boat "rigs" can advertise prices that appear low. Besides the freight and rigging charges, which are always applicable, these rigs come standard with very small outboards. Often the cost to "up-grade" to a larger engine is half of the base price of the rig.

So the cost of your outboard will be a major portion of the total expense for an AF4G or for any home-built power boat.

In my opinion, the power plant that would offer a builder of an AF4G the cheapest source of power able to plane the boat with a reasonable load would be an old OMC-built (Johnson, Evinrude, Gale) "Big Twin." Big Twin was a term used by Evinrude, specifically, but I apply the term to either the Johnson or Evinrude versions, and the Gale division made similar engines old under many different names (see "Gale Warnings" column.) The term "Twin" refers to the two-cylinder configuration of these engines.

The Big Twins made their appearance in 1951 @ 25 hp and went through some rather drastic changes until 1955, which would be the earliest model year that I would recommend. Horsepower was boosted to 30 in 1956 (the year in which the most outboard motors were ever built; about 750,000, compared to around 300,000 today) and then to 35 hp in 1957. In 1960 the horsepower was boosted to 40 and remained there until the early '70s.

A Big Twin from about 1955 until about 1970 or so has a lot to offer; a single, simple carburetor, compared to dual carbs on some of the 4-cylinder in-line competitors. A simple under-flywheel magneto, compared to the belt-driven magnetos used on the 4-cylinder competitors, and just a general simplicity that makes working on the engine less of a challenge.

Commonly-replaced parts, such as carb rebuild kits, ignition componets (for the "old-fashioned" points-and-condenser ignition system), water pump impellers, propellers, etc., are all readily available and fairly cheap compared to parts for more recent engines. And there are plenty of "junk" big twins around to serve as "parts engines."

Although physically larger than some late-model engines of comparable horsepower, the old Big Twins are almost never any heavier, and are sometimes lighter.

And finding these old outboards is not very difficult, as many were built. In fact, it is usually easier (and cheaper) to find, say, a 1959 35 hp rather than a 1959 18 hp. Anglers are always looking for engines of from 10 to 20 horsepower, and finding engines in that particular horsepower range can sometimes be difficult. But few people want the old 30's and 35's, so they generally sell for less.

The "down-side" to the big twins? Well, they drink a lot of gasoline and end-up dumping a good portion of if into the water. Since I do not get to spend anywhere near as much time on the water as I would like, the increased fuel consumption is not a significant factor to me.

And one can buy a heck of a lot of gasoline with the difference in price between an old big twin and a brand- new 4-cycle outboard.

And if given a choice, which engine would you prefer to shear the lower unit off of on a big submerged rock?

As to the harm to the environment, that is a decision you must make for yourself. Since I have driven nothing but 4-cylinder manual-shift autos without air-conditioning from 1982 until the present (while the rest of America went from driving big station wagons to big conversion vans to big sport utility vehicles) I feel I have a little "slack" on the boat motor issue.

The Big Twins were available with remote controls or with tiller control, but are very easy to convert back and forth; in fact, you can have one set-up for remote control from the forward end of the boat, but also with a tiller in case you need to control the motor from the cockpit. The Duckworks columns (Part-I & Part-II) on remote controls apply to these engines and will provide details as to what equipment is needed. Tillers are available through used-part sources and are easily installed without losin remote-control ability.

There are some Big Twins that I would recommend that you avoid; 1960 and 1961 were the first two years of the 40 hp version and had some major stuctural problems; i.e. a reputation for shearing flywheel keys and even breaking crankshafts. Because of these problems, the powerhead for the 40 was completely re-designed for 1962, and the '62s and later 40's are very good engines.

During the mid to late '60s, the 40 was available with electric shift; rather than using a push-pull cable ("bowden wire") to control the shifting, these versions used electro-magnets in the lower unit for shifting. As one might expect, water leaking into the lower unit, while never a good idea, was a real disaster for electric shift engines. In additon, the electric shift models required a special control box for remote controls. A quick way to tell the difference between an electric shift and a mechanical shift 40 is that the mechanical shift version has a shift lever on the Starboard side of the engine, while the electric version will not have the shift lever. Also, the lower unit of an electric-shift model will appear much more "streamlined" than the lower unit of a mechanical-shift version. I would avoid these electric-shift versions.

The only advantage that the electric-shift versions had was that they came standard with a battery-charging generator (not an alternator), whereas the generator was an "extra-cost" option on nearly all the other versions, and it was an option that few people bought. I have had many of these engines and have never had one with a complete charging system, which would include a voltage regulator in a metal box which mounts inside the boat.

In addition, there were "standard" and "deluxe" models of these engines. The deluxe models usually had fancier trim and paint, were almost always remote-control versions (but could still be converted to tiller control) and usually came with electric start (although electric start could often be had as an extra-cost option on standard models.) Sometimes the fancy version was fitted with a fuel pump while the stnadard version used the old pressurized fuel tank (see "pressure tanks" column.) Evinrude usually called their fancy engines "Larks" while Johnson orignally called their fancy versions "Javelins" and later called them "Super Seahorses." The Term "seahorse" was applied by Johnson to virtually all of their outboards after 1929, and does not identify any particular model.

These fancy versions also often featured a very "fat"- looking "mid-section" that was of double-wall construction in order to reduce noise and vibration.

As mentioned, electric start was an option, and many of these engines have it, or it has been added. Electric start can be added to a Big Twin that does not have it, but if electric start is important to you, I suggest you choose an engine with it already fitted. The electric-start versions also had a metal box that mounted inside the boat; this contained the solenoid for the starter, and if one is searching for a generator-equiped engine, do not confuse a solenoid box for a regulator box.

The 35 hp and early 40 hp models were equipped with compression-relief valves that were supposed to make manual-starting these engines (all of which came with recoil starters) easier. The compression release valves where incorporated into the cylinder heads, and were activated by a metal arm that extended up to the top of the recoil starter. Often this arm is missing, and anyway, I never really throught it helped all that much. Hand-starting a 35 or 40 is certainly harder to do than starting a 10 or 15, but it is also certainly not impossible; I used to do it when I did not feel like carrying a 12 volt (6 volt in the case of 1956 and older models) battery around. Being equiped with the magneto, none of the mechanical-shift versions of the Big Twin require a battery to actually run; it's just for the electric start and any accesories you might have on the boat. Hand-starting a well-tuned, warmed-up Big Twin is often a "one-pull" proposition.

While it usually is not necessary, I will point out that a couple years ago, I purchased a complete set of bearings for the lower unit of a 1956 30 hp at an industrial bearing supply house for about 50 bucks; they were standard, off-the-shelf bearings. On the other hand, the '57 and later lower units have a revised bearing scheme that is a whole different "ball game" to deal with, and I suggest that you be a little more selective with those lower units. Fresh lower unit oil, rather than old oil, or no oil, or water, should flow from the lower unit, but be watchful for signs that the oil was changed 15 minutes before you arrived to look at the motor.

Also be aware that some "parts swapping" may have occured on an outboard motor nearing 50 years of age, and, for example, the lower unit on a particular Big Twin may have been swapped from a motor of a different year. That could cause problems that I won't go into here. Just something to be aware of.

Often the wiring harness that connects the motor to the solenoid box, regulator box, and battery, is in tough shape or even missing. This is not a big deal as these engines are fairly simple to re-wire, and a future column will deal with wireing one of these engines. A usefull bit of knowledge is that if the harness is disconnected from the engine, the engine can be manually started and run, but you will need to "choke" it to shut it down. With the harness removed, the ignition is always "on." This, of course, only applies to those engines that were fitted with electric start; manual-start versions did not have an external wireing harness.

A missing solenoid can be replaced with an automotive version. There is a difference between marine and automotive solenoids, but for a trailer-kept boat, and/or one where the battery is disconnected when the boat is not in use (always a good idea) the difference will cause no trouble.

Since the wireing harness and boat-mounted solenoid box makes it a bit difficult to move the engine from boat-to-boat, I have wired-up some tiller-steered versions of these egnines with an automotive solenoid mounted under the engine cowl, and mounted a push starter button on the front of the engine, so the only wires that enter the boat are the two battery cables.

There are a couple of distant "cousins" of the big twins, the mid-to late 1960's 28 hp and 33 hp. Most of the above also applies to this series of engine, which is a bit different than the Big Twin series, but not in ways that would really affect a user. Mainly, one must be sure that the rubber motor mounts on the 28 and 33 are in good shape, because if the upper mount breaks, the powerhead could drop slightly in the clamp brackets and break an oil line hose nipple off the front of the crankcase. This nipple can only be replaced by dissasembling the powerhead and by drilling and tapping for a new nipple.

All of the previous columns dealing with carbs, magnetos, recoil starters, etc. apply to the Big Twins. The only real differences bewteen a 1955 25 hp and the 1955 5-1/2 hp featured in the "Start to Finish" series is the size of the engine.

For those who think a 1958 engine may not be "reliable enough" for everyday running, be advised that I run a 1957 Johnson 18 on my AF4 (except when running on lakes with a 10 hp limit; then I run a 1956 Johnson 10 hp). This engine, over several years of use on different boats, has never let me down. I keep it "tuned-up" and I don't wait for parts, such as pump impellers, to fail: I replace them when they have had a "good run."

Probably the best place to learn about these Big Twins, to ask specific questions, and even to buy engines, is at one of the many swap meets sponsored by the Antique Outboard Motor club, Inc. They have a swap meet schedule posted on their website. Admission to the swap meets is almost always free and open to those with an interest in old outboards.

Although "show-room-new" Big Twins are real collector's items, a beat-up-looking old one, that may be in good mechanical condition, will not have many collectors drooling at a swap meet. But it may be perfect for your "cheap power" needs. And a "beater" Big Twin can have it's appearance much improved with a re-paint, either with automotive touch-up paint of a color which comes close to matching the orignal paint, or with custom-mixed exact-color paints avialable through the Antique Outboard Motor Club.

With reproduction decals applied, a Big Twin can be made to look good as new if that is the desired end result.

Keep in mind, however, that an old big twin that looks like junk may very-well BE junk. Usually, the collectors at a swap meet will give you an honest evaluation, especially of an engine than another collector is trying to sell you. But few of these old engines were run enough hours to actually be "worn-out;" if there is damage, it is most likely due to neglect or abuse, and an engine exhibiting signs of either is best passed-by for a better example, or bought at a low price for "parts' use.

Probably the worst place to buy one of these engines is ebay. The shipping cost alone will probably amount to more than a cosmetically-imperfect swap-meet engine will cost. And I have seen many engines on e-bay, accompanied by statements to the effect that, "I am no expert but it looks OK and complete to me" that had obvious major faults apparent to me.

The Old Outboard Book, mentioned in this colum many, many times, would provide much useful information for identifying the various models and years of these big twins, and the Old Outboard Service Manual (Volume 1 for engines up to 30 hp, and volume 2 for engines over 30 hp) should provide all the assistance a slightly-mechanically-inclined boatbuilder would need to do repairs short of a major over-haul.



Click images
to enlarge

1958 Evinrude "Deluxe"

1958 Evinrude "Standard"

1956 Johnson Standard

1956 Johnson Javelin

1955 Johnson 25

1951 Johnson 25

1957 Evinrude 35

1956 Johnson 30

Mid 60's Evinrude 40

Early 60's Rvinrude 40

Nice 1957 Johnson 35

1959 Johnson 'Super Seahorse'

Another view


External harness

parts engine