Intro:
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.)
The Task:
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:
The Drive System
(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 forward,
( 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:
- 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.
Detail:
Load Bearing
MountThe 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.
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.
Lateral SupportTo 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.
Pitch StrutParallelism 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.
Electrical System
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 themselfs:
1.) How to get rid of hot gases without
burning a hole in the bottom of the craft.
( Boating)
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 muffler.
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. |
