There is a continuos need for a
reliable, compact, lightweight Hovercraft / Inboard (boat) engine in
the 100 HP category. The fuel injected, overhead-valve Subaru
opposed-cylinder flat-four might be a great choice for this purpose.
Why the Subaru? Besides the good reputation that it will achieve
200.000 plus road miles it is a robust, reliable, lightweight engine -
in the last is the beauty! Block, head, and bell housing are aluminum
and weigh about 279 lb. A Hurt transmission, which nicely matches the
engine output weighs 28lbs. (It, too, has an aluminum housing.)
Start by shopping for the EA-82
Subaru engine in your local salvage yard. Look for low milage 1985 -
1986 Subaru, fuel injected, overhead cam version equipped for an
automatic transmission. You will find them in the 400,- to 800,- price
range depending on their age, condition and mileage. Most recent www
search resulted in an 650,- estimate + S.H. While out scouting, begin
your search for a rebuilt model HBW 150-1.5 Hurth transmission. A new
one costs around 1.200,- , but you can get a rebuilt one for 800,- to
900,- including the vibration damper that will be bolted to the
flywheel and has a splined hole to accept the input shaft of the
transmission. ( The "-1.5" in the model number indicates a forward
output ratio of 1.56)
It is very important that you
acquire a Haynes "1980 - 89 Subaru Automotive Repair Manual". This has
a wealth of information describing the disassembly and reassembly
sequence, specifications, torque requirements for fastenings, timing
procedures, and other vital information. Try to understand each task
ahead. In addition to specific parts replacement guidelines, the manual
is a guide to the accepted rebuilding procedure. If possible, before
purchasing and dismantling the engine, it is a good idea to check the
compression (this procedure is spelled out in the manual and may be
performed without actually running the engine). This test will give an
indication of engine's general condition, and of any internal wear.
Worn piston rings, scored or worn cylinder walls, blown head gaskets,
or sticking or burnt valves, are potential culprits. Before any
attempted is made to convert the power plant for Hovercraft / Marine
use, it is advisable ( if not necessary) to disassemble the major
components, determine their general condition, and replace them if
necessary. The tools required for this , with a few exceptions, are
listed in the Haynes Subaru manual. More in depth work will require
certain special tools, many of which can be rented from a local parts
jobber specializing in automotive work.
While the engine is disassembled,
degrease and clean all surfaces - including carbon deposits. Not only
will this prepare the parts for future painting, but it will make
working on them a more enjoyable task.
A word of caution: Never use a
caustic solution when cleaning aluminum, and always coat internal
threads with an anti seize compound. To marinize the engine you must
modify these systems:
(Hovercraft) To allow your CG to
be in balance with the craft and have a straight belt connection to
your prop shaft install the engine with the transmission facing aft,
(Boating) To accommodate a midship
engine location in a small boat, and still maintain a modest 12 degree
angle, the propeller shaft must pass beneath the crankcase. This
results in positioning the engine so that the transmission faces
( both ) with the power being
delivered to the propeller by means of a molded rubber cog belt having
positive slip proof engagement without lubrication or high belt tension.
Why did we specify an engine equipped
with automatic transmission? Because the manual shift transmission case
and mating half of the bell housing is all one piece, and there is no
way to separate the two. The automatic transmission case, on the other
hand ,is a bolt-on attachment to the outer half of the bell housing.
Once this is disassembled, there is no use for the torque converter and
its drive plate, and these parts may be discarded- to be replaced by a
manual shift flywheel and clutch cover from a model EA-82 Subaru engine
(these parts may also be obtained from a salvage yard). Following a
simple rework consisting of removing the finger springs from the clutch
cover - these to be replaced by a Hurth vibration damper - the new
components can now be mounted to the engine's crankshaft. The
transmission is attached to the flywheel bell housing using 1/4"
thick aluminum adapter plate. The splined input end of the transmission
engages the vibration damper. The output end of the Hurth is designed
for a flexible coupling. As we have no use for a coupling in this
instance, a simple turned stub shaft is attached to accommodate a
commercially available sprocket for the cog belt.
(Hovercraft) Although not part of the
conversion, it will be necessary to support the prop steel shaft on
both ends with self-alining sealed ball bearings designed to absorb
both the thrust and radial loads supported from engine mount forward
and support fins aft.
(Boating) Although not part of the
conversion, it will be necessary to support the inboard portion of the
propeller shaft. This is best accomplished by a welded aluminum member
containing two back to back flange mounted self-alining ball bearings
designed to absorb both the thrust and radial loads. This assembly is
then securely bolted between the boat's fore and aft stringers.
The Mounting System
The engine, when installed, is
completely isolated by rubber shock mounts. Even the prop is
rubber-belt driven, so very little vibration is conveyed to the
craft / boat itself. The mounting system serves three functions:
The weight and torque of the engine
are conveyed to the craft's stringer through a transverse steel
weldment bolted to the stringers. This weldment, referred to as the
engine mount, has slotted holes for attachment to the stringer, and
jack screws bearing upon a steel plate atop the stringer to adjust the
tension of the cog driven belt.
- It bears the weight of the
engine and absorbs torque
- It provides lateral support to
prevent oscillations in the vertical axis.
- It maintains parallelism
between the engine and prop shaft.
Angled channel shaped members welded
to the top of the engine mount serve as support pads for the engine's
rubber isolation mounts, which are attached by a single nut with lock
washer to a stud provided in the mount.
To prevent oscillation of the engine
in its vertical axis, it is necessary to add a lateral support. This
support is located 13 3/4" aft of the load bearing mount and is
comprised of a rubber-bushed support rod attached between the engine
block and the portside engine stringer.
A 1/8 X 1 X 1" strructural steel
angle bolted to existing tapped holes in the engine block will provide
attachment for one end of a 3/8-16 continuous-thread steel rod. The
opposite end will be supported by a flat 1/4" aluminium plate bolted to
the boats port-side stringer. Doughnutshaped rubber bushings applied to
either side of both attachments will isolate the boat's structure from
engine vibrations. These rubber bushings are backed up with heavy
washer on either side and a tubular-steel spacer cut to a length to
span the distance between the engine and the stringer. Hexnuts at the
ends of the threaded rod serve to compress the rubberbushings and
complete the assembly.
Parallelism between the prop shaft
and the engine shaft is maintained by adjusting a turnbuckle within a
rubbermounted strut, the strut being attached to the top of the
flywheel housing at one end and a reinforced transverse beam on the
craftat the other. As there is considderable flexibility in the
load-bearing rubberengine mounts (item 17 in attached graph.), there is
ample angular displacement to maintain parallelism.
The pitch strut is a modified
pitching stopper rod acquired from a 1984 Subaru (on the car, it is
located between the firewall and the top of the bell housing). The
modifications require the rod to be cut in half and a commercially
available turnbuckle welded to it. Angular brackets allow attchment to
the craft's structure.
The engine you purchased had many
automated devices and sensors including the ignition, all controlled by
a "brain box" or electronic module,located somewhere in the trunk of
the vehicle. To avoid the complexity of handling bundles of wires,
hooking them up, and conducting checkout procedures, the electrical
system for the conversion has been basic and simple.
Breakerless ignition is a great
improvement over the earlier breaker type, and many units are available
in the aftermarket. You can purchase one from J.C. Whitney Co.; it is
very easy to adapt following the instructions from the supplier.It's
also recommended you replace the existing ignition coil, ballast
resistor, plugs, and ignition wires with new ones. A safety switch,
activated by the transmission's shift lever, prevents inadvertent
engine starts while the transmission is in gear.
Having dispensed with the "brain
box", the engine must be converted to a carbureted version. The
carburetor chosen for this application requires a remotely located
automatic-choke unit. This device contains a bimetallic spiral spring
which, when heated by an electrical current with the engine running,
will slowly cause the choke to open.
The wiring diagram shows the wire
terminations, and AWG wire sixes, and all are labeled as to their
destinations. All wires must have at least stranded copper conductor
with PVC insulation and be fitted with crimp-on, insultated ring-type
terminals. More than two wires are to be carried in flexible split-wire
loom supported on loop clamps. It's good practice to apply wire markers
to the ends of each wire using a number code. To be of value, this
number should be marked to the corresponding wire on the wiring
diagram; this will be a big help when you wire the whole craft.
The Exhaust System
As the engine's exhaust exits
downward close to the bottom of the craft, two problems present
1.) How to get rid of hot gases
without burning a hole in the bottom of the craft.
2.) How to elevate the water-cooled
exhaust well above the surrounding water in which the boat rides.
Both problems are solved simply by
injecting engine cooling water into stainless-steel mainfold tubes
leading to a water-lift muffler that carries the water and gases well
above the waterline.
The stainless-steel mainfold tubes
are fabricated from 316L stainless-steel tubing having a 90 degree
elbow at the inlet and another 90 degree elbow rotated at right angles
at the exit end. The inlet elbow has a welded exhaust flange mating
with the engine exhaust port, as well as a 1/2" -diameter
stainless-steel tube welded into the bend of the elbow; this tube
sprays cooling water, which mixes with exhaust gases.
The exit elbows of the mainfold tubes
are connected by watertight coupling to the sides of a water-lift
These tubes are structurally robust
and designed to support the muffler without further attachment to any
part of the boat.
The water-lift muffler is a molded,
"glass-epoxy-reinforced, watertight enclosure containing two opposed
entrance pipeson the sides and a larger vertical fiberglass standpipe
extending within an inch of the bottom.
As exhaust and water enter the
muffler, water begins to accumulate, as soon as the water covers the
open end of the standpipe, pressure exceeds the head created by the
elevation of the curfed, reinforced, flexible exhaust hose well above
the waterline, then the combined water and gas are directed downward
and overboard through the transom exhaust port. This results in a back
pressure, to be sure, but this is rearly over 3/4 psi, which is quite
acceptable. The water-lift muffler can be built in a couple of days. It
is compromised of two "glass-epoxy shellsmolded within the interrior of
two inexpensive plastic waste baskets, acquired from almost any
department store. Once cured and extracted, the molded shells are bored
to accept commercially available fiberglass exhaust pipes. These
individual parts are then joined using thickend epoxy as adhesive in
conformance with the dimensions of the drawing.
The Cooloing System
This engine has a closed,
recirculating freshwater cooling system. The primary advantage of a
freshwater system is that contaminated water and / or seawater are
never introduced into the aluminium engine block, which would be
devastating over time.
Basically, the system is quite like
that of an autombile's cooling system. Water mixed with antifreeze ( a
good rust inhibitor ) is circulated at a thremostatically controlled
temperature throughout the engine whereupon it is directed to a
heatexchanger, the equivalent of a car's radiator; the water is than
routed back to the engine.
The vertically mounted heat exchanger
in the application contains many small - diameter copper tubes
through which raw water passes on its way to mix with the exhaust gases
and out through the boat's exhaust line. The space surrounding
these tubes contain's the engine cooling liquid. As both liquids are
being circulated by their seperate pumps, the engine heat is
transferred or given up to the cooler raw - water tubes. In addition to
this, an expansion tank is affixed to the upper portion of the heat
exchanger to acommodate the volumetric changes due to temperature
differences from a cold start to a running condition. A pressure fill
cap is used to prevent boiling and loss of coolant.
In practice, raw water is picked up
near the after portion of the boat's bottom and drawn upward through a
screentype strainer, then through an oil cooler,then to the inlet side
of an engine-belt-driven impeller-type pump.
The outlet from the pump is directed
to the heat exchanger. Once leaving the heat exchanger, the water is
guided to a reducing tee, where the stram is divided to enter the twin
mainfold pipes, joining with the exhaust gases.
Since the raw water exits into the
exhaust mainfold tubes which are locatedbelow the boats waterline, it
will be necessary to provide a siphon-break valve installed at the
discharge side of the raw-water pump. Without this device, water could
fill the muffler by siphon action and eventually flood the engine upon
shutdown. In general, all hose clamps should be stainless-steel (please
verify that the screw is as well ss) and unless otherwise
specified, all fittings should be brass.
The Fuel System
The fuel-injected version of this
engine requires six electronic engine controls including a costly
electronic control unit (ECU) along with seven enviormental emission
control devices. Since a boat never has to contend with continual
variations of engine speed, hill conditions, altitude changes, and
severe temperatures, a simple single-barrel carburetor matched to the
displacement of the engine offers the best alternative, providing ease
of maintenance, reliabbility, and low cost.
As the engine will be operating on an
incline due to the angle of the propeller shaft, it wil be necessary to
provide a wedge beneath the carburetor to create a horizontal level of
fuel chamber. Since the temperature of the intake mainfold is well
below ignition temperature, the wedge may be fashiond from closed-grain
hardwood such as maple.
In order that the carburator may have
an automatic choke feature, it is only necessary to attach an electric
thermostate choke element to the carburetor choke linkage.
The one remaining task task is to
plug the fuel injector ports on the intake mainfold. Only two simple
aluminium componentsare requierd for each of the four cylinders. When
the occasion arrives to install the engine, it will be necessary to
providethe following : fuel tank, tank vents, filler pipe, fuel line
hose, electric fuel pump, and fuel water strainer (a fuel shutoff valve
is a good option, too although not reqierd by the USCG if the
carburetor conection is above the level of the fuel tank and the fuel
tank and the fuel line is less than 12' in lenght). Not knowing the
specifics of your craft, it is best that you order these items, all of
which may be found in the many discount marine catalogs or stores.