| By: Scott
Fratcher - Marine Engineer/Captain
Changing the main engine of a boat sounds like a huge project.
Cranes, plans, alignment, choosing the right engine, it can all
seems overwhelming to the yachtsman.
In reality for the DIY changing a main engine in a yacht
is relatively straightforward. You don’t have to learn all
the special skills of a master mechanic as you never rebuild or
even work on the diesel engine.
It’s a simple matter of removing the old engine, rebuilding
the engine mounting rails, and then bolting the new engine in
place. It might sound complicated, but it’s really rather
simple.
Do it yourselfers often take over three months to get their engines
installed. I have devised a system outlined below where we can
change a main engine in just one week. The one-week engine change
means the boat, and often the family living area is only torn
up for seven days.
Step 1-Buy New, DON’T REBUILD!
This is a very important point. Boat owners will often look
at their worn out, leaking, engines wanting a rebuild of the old
trusted “friend”.
Unfortunately the numbers don’t add up. Consider that a
rebuild job will normally cost about half the price of a new engine.
Most rebuilds only come with a short term and local guarantee.
In other words head to the islands and if complications arise
the local mechanic that rebuilt the engine will want the engine
returned to his shop or marina for service.
I come across engines all the time on the cruising circuit that
have five hundred hours after a new rebuild. They are blowing
and burning oil leaving the owner back to square one.
Besides, the price estimate I just gave is only the cost of rebuilding
the block. The old heat exchanger, oil cooler, gear box, alternator,
and high priced injection pump may still have five thousand original
hours on them. Rebuild all of the extra components and your well
on your way to the cost of a new engine.
Measure before you pull the old engine
Ask many “do it yourself” yacht owner about an engine
change and the sticking points will be:
1. How to measure for the new engine.
2. How to move the new engine.
3. How to make a perfect alignment.
Lets start with how to measure. This semi-simple process takes
about two hours and is outlined below.
The Measurement
The measuring technique is the heart of an engine change. The
first thing you will need to do is find the existing height of
the crankshaft center to the bottom of the existing flexible engine
mounts. To do this take a flat edge and lay it across the engine
beds. Use this straight line to measure down from the crankshaft
center to the engine bed line.
This is your first important figure. This is the line of the
prop shaft progressed forward. If the gearbox has an offset, or
a drop, then you must add or subtract this figure to your final
measurement.
Now look at the drawings for the new engine and find the distance
from the center of the crank to the engine beds. Add in the gearbox
offset if any and you should now have two separate measurements.
The difference between them is the thickness you will have to
make up, or cut down from the excising mounts to make the new
engine fit.
Simple Now that you know
Strangely after many engine changes with this system I have not
come across an engine bed that needs to be lowered. For some reason
they all have to be raised 10mm to 50mm.
The difference between the old engine and new is the all-important
measurement. If you got this right then you can have the “adapt
a rail” pre-made before you remove the old engine.
Lift the old engine, bolt down a pre-made piece of steel rail
(to make up the height difference), and set the new engine in
place.
Often two inches is the magic number. If you got lucky and the
new engine mounts sit exactly two inches high then buy a piece
of two by four steel extrusion 5mm or thicker. Lay the new rail
right over the old engine beds, bolt them down, and set the new
engine in place. Sometimes I have to take the extrusion to a shop
and have it cut and welded to the special thickness I need. Either
way make this particular, all important adapt-a-rail before you
lift the old engine.
Tip-While the old engine is out it is the perfect time to paint
the engine area white, and maybe service the bilge hoses or anything
else that runs under the engine.
Tip 2-Consider installing a series of lights that illuminate the
engine from below. Your new engine is going to be very clean and
nothing helps keep an area clean like really good lighting.
Price saver
Often the DIY can save a bit of money by measuring, and doing
the heavy lifting themselves. Once this is complete call your
mechanic to do the alignment and inspection. This can be a win/win
for all. The local mechanic gets some of the work and catches
the basic mistakes, while the owner pays to have the difficult
part of the work completed and yet does the easy work himself.
The Rest of the Fit
You will have to measure width, height, and depth of the new
engine along with the motor mounts, but most modern engines are
much smaller than the twenty year old diesel you will be removing.
The only time size has been a problem has is when we remove a
small engine and replace it with a much larger model. The popular
Perkins 4-108 is now replaced by a Yanmar that is about 2/3rds
the size of the original.
The 56hp Yanmar is about the same size as Perkins 4-108 giving
almost half again the horsepower.
Lifting the Old Engine
The lifting, and removal of the old engine is the next step of
what some do it yourselfers may find overwhelming.
I almost always lift from the main boom supported by halyards.
I attach a block and tackle to the lifting point and then run
the bitter end to a winch.
I use a land crane to set the engine on deck then take over myself
with a boom lift. I always use two lifting points on every aspect
of the lift. If any single line were to break the engine would
not fall. The lifting lines are tailed to the two largest sheet
winches on the boat
The crane lifts the engine onto the yacht’s deck. Unless
you really trust your crane driver it’s often better to
move the engine by block and tackle the rest of way to the new
engine beds where the movement can be controlled with precision.
Lifting the engine using the boat’s rig. Pay particular
attention to the gooseneck or connection between the boom and
the mainmast. As long as the boom is in center line with the boat
the load should be in compression, or pushing into the mast. The
problem can occur when we attempt to swing the boom out to the
side. The load on the gooseneck turns from one of compression
to side load. Inspect the gooseneck carefully and keep the load
inline with the mast as much as possible.
Throttle connections
A common challenge with a new engine is a reverse throttle action
on the injection pump. At the helm push might become pull, or
however you move your throttle control now may be reversed. We
can choose to get used to his new throttle linkage, or we can
build a throttle reversing mechanism.
This reversing mechanism should not be taken lightly. Engine
control systems must be 100% dependable. If the throttle linkage
were to fail during docking it could cause an expensive accident.
For this reason take your time and over build all shifting/throttle
linkages. Notice in the photo we used 4mm plate on the reversing
system and red Locktight on all bolts.
Occasionally it may pay to haul the vessel for the engine change,
but this is only if other work needs to be performed, or if the
prop and maybe shaft are to be changed. Otherwise it’s almost
always easier to do the engine change while the boat is at the
dock.
Tip: If you’re lifting the engine on it’s end then
consider slipping a plastic garbage bag right over the bottom
to catch any oil drips.
Tip2: Cut up a piece of plywood to cover the floor around the
work site. Often times the new engine arrives in a plywood box
that can be cut up to use as material to protect the floors.
Engine Alignment
The final engine alignment is often the last tricky item on the
DIY’s mind. Will all the measurements be correct? Will the
shaft simply slip onto the new gearbox?
By learning a few engine alignment tricks you can save a big
chunk of money and time by preventing the rebuild of gearboxes,
broken shafts, or worn couplings.
Remember, if your on a new engine installation we should align
the engine before we make the holes to bolt the mounts in place.
Only once the engine is perfectly aligned should the first mount
be bolted down. Then the alignment is checked again. If all is
still correct then bolt another mount in place and so on till
all the mounts are securely bolted in place.
The first step to aliening an engine is to locate the prop shaft
in the middle of the stern tube. I like to start with the shaft
just over center (at the 3/5ths mark) so as the flexible engine
mounts sag over time the shaft will remain in the center of the
stern tube.
You may have to block up the shaft to keep it in place. Remember
the engine aligns to the shaft. Once the shaft is in place the
engine should follow, not the other way around.
Clean both flanges using a wire brush. Push the prop shaft flange
against the gearbox flange. Ensure the centering rings set in
place. Give the flanges a twist back and forth to make sure they
are seated well together. Slide a feeler gauge between the flange
faces. Measure and mark the area of greatest gap.
Before you proceed rotate the prop shaft one hundred and eighty
degrees or a half turn. Check the feeler gauge readings. They
should remain constant. If the readings changed from our first
measurement then the shaft is bent or the flange is bad. If you
find a bent shaft and it exceeds the four thousands tolerance
of the alignment then fix that problem before you continue with
the alignment.
Often times we suspect the shaft is bent or some other aspect
of the drive system is out of true. This simple shaft rotation
test confirms the problem or sets our mind at ease.
Adjust the engine mounts a bit at a time to close the gap in
the flange faces. Keep all four mounts as even as possible. Keep
checking alignment till you are within .004”. At that time
tighten all the mounting bolts and check alignment again. Wiggle
and shake the engine as much as you can.
On larger engines you may have to get two people pushing and
pulling to get the engine to move around. The idea is to make
the engine settle on her mounts. Check the alignment again and
adjust your mounts to fix any gap that reopened. Keep repeating
this procedure until the engine is sitting in perfect alignment.
Expect to take about six hours to do a perfect engine alignment.
A good experienced technician can normally complete this process
in about an hour. Of course this means all the bolts are loose,
clean and access is easy.
Tip- Resist the urge to move a single mount that builds up a
little pressure on the opposing mount to make a small adjustment.
When the rubber in the engine mounts get hot it will soften and
fall out of alignment causing the engine to begin vibrating.
Tip- If you find you have to lay on top of the engine to reach
the flange to measure your weight will almost assuredly change
the compression of the mounts and thus your alignment. If this
is the case then you will have to find some clever way to keep
your weight off the engine while you test the flange.
If I have to lay over the engine to work on it lay some carpet
over the engine to help keep comfortable. If you’re comfortable
you can almost always do a better job.
Exhaust system
The next step in the engine change is hooking up the exhaust
system. Although this seems straight forward some thought should
be put into the part of the project. If your new engine has a
higher horse power than the original engine its possible the exhaust
diameter will need to be enlarged. Consider this project carefully.
It can cost more in labor to enlarge the exhaust system than to
change the engine.
Tip-Often the exhaust manifold outlet on a new engine will be
on the opposite side as the original. If this is the case a simple
solution to connect to make an S curve from exhaust hose and two
45 degree elbows that allows an easy, inexpensive connection to
original system.
Engine panel
Most new engines come with a “plug and play” wiring
harnesses. In other words the wire loom installation is simply
a matter of pressing together the supplied connections. Still,
the wire loom should be secured to the engine with wire ties to
prevent vibration. Where the wire loom passes from the vibrating
engine to the rigid hull a loop of extra cable should be left
to take up the vibration. The wire loom should be secured every
eight inches along the complete rout to the engine panel. This
may seem like a lot of securing points, but in years to come all
new wires from the panel to the engine will eventually follow
the wire loom possibly adding up to a large amount of wires.
Preventing water backing up into the engine
The most common cause of damage to a marine engine is salt water
intrusion due to poor installation of the water cooling hoses.
In order to reduce the chances of filling a new engine with salt
water remember:
- Put in an anti siphon loop between the engine water outlet
and the exhaust elbow inlet
- This loop should be at least a meter above the outside water
line
- The loop should be on center line
- The top of the loop should have anti siphon break, or better
a anti siphon loop that feeds a small hose that trickles somewhere
the operator can view, such as the cockpit floor.
Tip-Resist the urge to tee into the sink drain as a place to
“trickle” the anti siphon water. More than one new
engine has been ruined when the sink was plugged and filled with
water to wash the dishes thus sealing the anti siphon loop.
Remember, just because the engine did not flood for the first
year does not mean the water system installation is correct. It
may simply mean the rubber impeller in the salt water pump is
blocking the flow of seawater at rest. The day may come when the
impeller wears and allows water to creep pass filling the exhaust
system and the engine with destructive seawater.
Take one last look at your installation. Check for loose bolts,
leaks, drips, oil in the engine and gearbox, and coolant in the
heat exchanger. If all is ready then were ready to sea trial.
Tip-On initial start up be sure to hold the stop lever and turn
the engine with the starter till oil pressure builds. This will
lubricate the dry engine before the first start.
Sea Trial
When you finish your installation it’s time to test. If
this is indeed a new installation then the manufacturer representative
should be on hand to activate the warranty.
Have the engine access open and be ready to observe the engine.
Hold the stop button and turn the engine over for a few seconds.
Did the oil pressure build? Did the engine sound smooth? If so
start it up and let it idle. Check the engine control system and
look for leaks. Follow the exhaust system to verify it all looks
and feels right.
Put it in gear at low rpm’s. Does the back of the gearbox
make little circles following the prop shaft? This is a sure sign
of a misalignment, bent shaft or other drive train issue. Take
the boat out for a test run. Will the engine reach maximum rpm’s
while driving the boat? This verifies the prop is of the correct
pitch.
When run at higher rpm’s does the engine shimmy and shake
or maybe pump for and aft? Not just vibration, but a cyclical
motion that is not present when the engine is run at high rpm’s
in neutral? If the engine sits smooth take one last alignment
reading at the coupling to verify your final reading.
Author profile-Scott Fratcher has served as Senior Technician
for Yanmar Engineering Services in Auckland where he used many
of the tricks shown in this article. More information is available
Yachtwork.com, or see “How
To Make Money With Boats”
Engine change - info part 2
Note- We no longer change engines. The information presented
is just for general use of the boating public.
We have perfected the one week mobile
yacht engine change. Below are some examples of our system and
work.
Step 1
We asses the existing engine installation, the fuel reserve of
the vessel, the propeller apertures, the shaft diameter, the space
available for the new engine and access to engine service points.
With this information the owner can make a decision of what new
engine to install. This step normally takes about two hours.
Step 2
Scott measures the existing engine and compares this information
with the measurements for the new engine. This will tell us how
the new engine will fit on the old engine beds. With this information
we can design a set of engine rails to sit on top of the old beds.
Scott then makes a list of materials that the owner collects while
waiting for his new engine to arrive. The owner doing the shopping
and expediting saves money and time. This step normally takes
three to four hours of Scott's time and two to three days of shopping
by the owner. Depending on the yacht's location the engine may
be on the shelf (Panama City) or take up take up to two weeks
in shipping.
Removal of an old Mercedes 636. Notice
we have the floor and deck covered to protect the woodwork.
Step 3
With a pre-scheduled starting day Scott and the owner begin
removing the old engine. We normally have the old engine
out and the new engine rails in place by the end of day one. At
this point many owners choose to have the beds and open engine
area painted. If we schedule this before hand we can leave a lay
day for the paint to dry. If the owner is in a hurry we can just
let the paint dry overnight with fans exhausting the fumes.
Step 4
We lower the engine onto the new rails and begin alignment.
This is the slowest and most important part of the job. The lowering
of the engine must be done carefully to prevent scrapes and dings
to woodwork. Once the engine is on the new rails we slide the
engine back and forth to line it up with the excising prop shaft.
The shaft must be supported to place it just above center of the
stern tube. If all goes well at the end of day two l have the
new engine in place, sitting on the new rails, with the couplings
together and in line. Sometimes this takes until the end of day
three if the rails are especially challenging or the access was
restricted.
Step 5
Bolting it all down. Once we have the engine in place we can begin
to bolt the engine mounts to the rails. We have to be careful
here because if we bolt the mounts down in the wrong place this
wastes time and effort. We normally vice grip all four flexible
mounts in place and then start by putting in one single bolt.
Then we realign the engine to the prop shaft, re-clamp, and then
put in the second bolt. By repeating this procedure eight times
we now have the engine bolted in place and we are ready to begin
hooking up the water, exhaust, diesel, etc. In most installations
this will be completed on the end of day three.
Step 6
This day is normally the most fun and exciting for the owner.
We can see the light at the end of the tunnel as we begin hooking
up the salt water in, the diesel lines, the electrical, hooking
up the exhaust, and all the little things that make the engine
seem complete. By the end of day 4 we normally can start the engine
and test the shifting.
Notice everyone is starting to smile.
Step 7
Sea trial. If you thought yesterday was fun, just wait till we
put the engine in gear the first time and power up. No blue smoke,
smooth start, big bow wake, large speed over ground showing up
on the GPS, smooth engine, everything we had hoped for.
Scott always keeps a bottle of cleaner
handy!
Have a question about how to buy a boat cheap? How
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career counseling question? How to maintain your metal boat? Corrosion
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Special considerations
Sometimes engine changes can have special
circumstances. For example if the vessel had 40hp engine and the
owner wanted to replace it with a Yanmar 75hp then the exhaust
system may need to be enlarged. In the examples below you see
a Perkins 4-108 being replaced with a Yanmar 75 hp and a 2"
exhaust being enlarged to a 3". The prop was also changed
from an 18" to a 22". This vessel, a Passport 40 achieved
7+ knots from a dead stop in about 8 seconds. Amazingly we changed
another engine in a Passport that same season and only installed
a 56hp in that vessel. Both had the same top speed, but the 56hp
took almost twice as long to reach 7+ knots. For the vessel in
a seaway that should mean the ability to motor into a heavy head
sea with more punch.
And the boat is ready to go back into
the water.
This was the process of enlarging the
exhaust system and enlarging the prop. The old aqua lift built
into the keel had to be opened and a new cover plate with the
new SS tube installed. The old 2" through-hull was removed
and a new 3" put in it's place. Much of this through-hull
work was done expertly by Jason on Baggywrinkles.
Commonly asked questions
Question - What is this all
going to cost?
The cost of the whole package varies
wildly depending on Yacht location, equipment available to help
with the change, and how much the owner wants to do himself. With
all those varables we can start the pricing.
The cost of the installation process
normally runs about $400 to remove the old engine. $600 to build
the new rails, place the new engine in place and align. The hooking
up of all the extras is in the $750 range. This tends to be a
total package of about $1700-$2500 in labor to change an engine.
If the owner decides to add a dual alternator at this time they
can normally save about $200 as we will have all our tools on
hand. I must stress these prices are all general. Everything is
time and materials. If the yacht was built with difficult access
that takes more time and thus more money. The prices given above
are general, but realistic.
Question - I have a Perkins
4-108 and I want to change it with the Yanmar 56hp. Are there
any special considerations to think about?
This is a very common engine swap.
There are two added difficulties. First the exhaust comes out
on the port side of the Yanmar and the Starboard side on the Perkins.
Sometimes the exhaust hose will just swing over, other times we
have to make up a double 45 to reach the old aqua lift. This sounds
much more difficult than it tends to be. The second challenge
is the Yanmar has reverse throttle action on the injection pump.
Push becomes pull, or however you move your throttle control right
now will be reversed. The owner can choose to get used to his
new throttle linkage, or Scott can build a throttle reversing
mechanism. This can not be taken lightly. Engine control systems
must be 100% dependable. If the throttle linkage were to fail
during docking it could cause an expensive situation. For this
we take our time and over build all shifting/throttle linkages.
Notice below we used 1/4" plate on the system.
Question - Can I do some of
my own work?
Sure, you can do any and all work.
Scott works by the hour. You can have just a consultation where
Scott can give you a detailed explanation of how to do your own
work. Many cruisers are comfortable with much of there own mechanic
work, but the thought of a complete engine change seems daunting.
For that you could have Scott help with the consultation, remove
the old engine, build the new rails, then align and bolt down
the new engine. Then the owner can continue with hooking up the
water, power, diesel, etc. We have helped install engines by just
consulting and the owner took over. Other owners have had us change
their engine by just communicating with us by email while they
were in the states. The biggest single savings the owner can do
on an engine change is the installing of the new instrument panel.
This can take hours and needs lots of thought by the person who
is going to be at the helm. This is a common area of savings for
the owner.
Question - Does an engine change
ever take longer than ten days?
Ten days would be long engine change.
It all depends on whether more than a normal engine change is
needed. Some things that can cause delays are the prop shop sending
the wrong prop. Parts stuck in customs. Money transfers stuck
in international banks. Most of these types of difficulties don't
cost much money, just time. Things that cost money are the rare
situations where the engine beds need to be cut down, or even
more rare we find structural problems in the vessel itself. Also
the one week engine change is for the basic engine change. Many
times the owner wants to use the special access to the bilge to
change all the bilge pumps, hoses, and wiring. This all adds to
the total time, but this is normally planned out in advance.
Question - Does the boat have
to be hauled for an engine change?
No, definitely not. In fact having
the boat hauled makes the engine change more difficult. We need
a very calm anchorage or dock and electrical power. Most modern
yachts have an inverter and battery bank that will hold through
the project. The boats used in these examples had special reasons
to haul. For example one wanted to do a bottom paint and combine
both projects to keep the number of down days to a minimum. The
other was upping the horse power and thus needed a bigger prop.
Question - You mention Yanmar
often. Do you install other engines also?
Yes, we install whatever engine or
generator the owner chooses. We do tend to replace most power
packs with Yanmar as they dominate the 12-100hp yacht engine market
and I feel they are the best yacht engine made. Isuzu, Kabota
and Perkins are also available but they don't tend to have all
the options available. The other consideration is Yanmar is often
an off the shelf item. You can walk into the Yanmar dealer and
choose your engine on the day you want it. If they have to order
they can have the engine in as little as four days.
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