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
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
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
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
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
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
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
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"
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,
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
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.
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.