|How to maintain
a boat engine.
This page updated: March 2013
Sailnet - Tom Wood's "Drive Train Vibration"
"Drive Train Tune-Up" article by Harry Swieca in issue 2002 #1 of DIY Boat Owner magazine
"Diesel Engine Electrics" article by Don Casey in Mar 2002 issue of Blue Water Sailing magazine
BoatDiesel - Tony Athens' "Engine Life"
BoatDiesel - Ian Hodgkinson's "How to Beat the Detroit Overheat Blues" (acid flush of cooling system)
Sound Marine's "Some Common Questions" (about diesel engines)
New to Diesel Engines ?
The Boat Doctor
David Pascoe's "Diesel Maintenance Or Lack Thereof"
Engine maintenance article "The Three Hour Oil Change" by Don Casey
in 10/2000 issue of Blue Water Sailing magazine.
Don Casey's "Changing Engine Oil"
Mostly from "Good Boatkeeping" by Zora and David Aiken
(on Amazon - paid link):
From David Pascoe's "Diesel Maintenance Or Lack Thereof":
- Most damage to diesels is due to lack of cooling system maintenance.
Unlike gas engines, diesels will suffer serious damage from even minor overheats.
- Install an air-intake filter on your engine. Even inside
an engine compartment, dust, sand, fibers, salt in the air
can take a toll.
- Old 4- and 6-cylinder naturally-aspirated diesels are rugged and
dependable and somewhat tolerant of neglect. New smaller
high-performance turbocharged diesels are not.
- Clean around the oil filter before removing it,
to prevent dirt from getting in.
Wrap a plastic bag around it before unscrewing it,
to minimize oil spill.
Use wrench to remove old spin-on filter,
but only hand-tighten new filter.
- If your engine has a cartridge-type oil filter, you may be able
to buy an adapter or new filter base
to make it take a spin-on filter (better).
- Get a good brass hand pump for oil changing.
- If you use a dipstick pump for oil changing, use the largest
tube that will fit into your dipstick hole.
Also, maybe hose-clamp it on.
- When changing engine or transmission oil, measure oil
taken out so you know you got most of the old oil.
- Have a piece of clear plastic ready to
defend against hot squirting oil if a hose leaks or slips.
There could be oil and dipsticks for:
- Unlike an automobile engine (which gets hit by road dirt), a marine
inboard engine can and should be kept spotlessly clean.
- Tom Neale advocates: Every hour or so while running engine,
go in and listen, feel, smell engine. You'll catch problems
before they become serious. Also, use mechanic's stethoscope to learn
normal sounds of parts of engine, so you can diagnose it when
something is wrong.
- To check alignment of two pulleys, remove the belt and
lay a length of 1/2-inch dowel across the pulleys.
Or lay a straightedge across the faces of them.
- If outside of belt is much below rim of pulley,
belt is worn or wrong size.
- To check belt tension, grasp belt between thumb and index finger and twist it.
If less than 90�, too tight. If more than 90�, too loose.
- Turning pulley with a wrench should turn the belt;
if it doesn't, belt is too loose.
- After you replace an engine belt, run the engine for 3 minutes
before making the final tension adjustments.
- Tandem belts must be replaced together.
- After bleeding air from the fuel system, run engine
for 10 minutes to make sure all air is out.
- Oil stains/drops along bottom of engine
may mean leaking oil seals.
- Flush the raw water system with 1) the engine running
and 2) the engine providing the pump suction (not the
pressure of the water hose). Otherwise you may get water
through the exhaust system and into the crankcase.
- At least once a month, motor for at least 1.5 hours
at hull speed to keep engine healthy.
- Reduction gear.
- Injector pump.
Possible fuel filter locations:
Your boat may have more fuel filters than you suspect; don't overlook:
- Engine primary filter (water separator).
- Engine secondary filter.
- Engine fuel lift pump strainer.
- Fuel tank pickup tube strainer (remove it if you can).
- In-line sealed electric fuel pump may have filter inside it.
- Anti-siphon valve, maybe with a ball-and-spring check valve,
in the fuel line from the fuel tank.
- Genset filters.
- Outboard motor filters (tank, in-line, on motor).
If your engine has a cartridge-type fuel filter, you may be
able to buy an adapter (such as from ABC Precision Machining
to make it take a spin-on filter (better).
Possible oil filter locations:
Your boat may have more oil filters than you suspect; don't overlook:
- Engine main oil filter.
- Engine oil sump strainer (have to remove sump to get at it).
- Transmission/gearbox oil filter.
- Genset filters.
- Outboard motor filter (if 4-stroke).
Possible air filter locations:
Your boat may have more air filters and screens than you suspect; don't overlook:
- Engine (main intake, crankcase breather).
- Transmission/gearbox breather.
- Engine compartment vents.
- Outboard motor.
- Fuel tank vent.
- Holding tank vent.
- Water tank vent.
Adjusting the valve clearances (maybe every 2 years or so)
can improve performance ?
From John Dunsmoor:
> I'm thinking of measuring/adjusting my valve clearances.
> Simple procedure specified in manual, but I have to
> rotate the engine to different crankshaft positions.
> There is nowhere to put a big wrench on the flywheel
> or anything. Won't cranking the engine with valve-cover
> open spew oil everywhere ? How can I do this ?
Should not spew oil, not just bumping the starter.
Oil is pumped through the rocker arm shaft, then drains
back into the crankcase. So there is no real squirting per se.
Not to say that you can't get a mess going if you have the
valve cover off. I have actually adjusted the valve
on an engine while it is hot and running. With solid
lifters you can do a pretty good job just listening to
the clicking of the lifters. You do not want to overtighten,
you will burn a valve if they do not close all the way.
And with a diesel, it is running so slow, a little
loose is not much of a problem either.
From Gary Elder:
Throw decompression lever [or loosen all injectors],
so you can rotate the engine by hand.
Troubleshooting via exhaust:
BoatDiesel - Tony Athens' "What is white smoke?"
- Black smoke / soot = unburned diesel:
- Not enough air.
- Too much load (maybe reduce propeller pitch, clean propeller,
clean bottom, turn off watermaker/refrigerator, fix shaft alignment).
- Too much back pressure in the exhaust (corrosion, deposits, kinked hose).
- Too much fuel (defective injectors, incorrect injector nozzles,
bad injection pump settings). If injectors recently serviced,
check for too many washers under injectors.
- Low compression.
- Low-grade fuel.
- Valves not seating.
- Defective turbocharger.
- Clogged air intercooler (in air or water passages) on turbocharged engine.
- Blue smoke = burning oil:
- Overfilled crankcase.
- Plugged crankcase vent.
- Gasket, valve guide, valve seal, cylinder wall, piston, or piston ring problem.
- Defective turbocharger seal.
- Oil leak into air intake.
- Steam (rises, and disappears quickly without a trace):
- In a very cold climate, may be normal.
- Inadequate raw water flow (plugged strainer, bad impeller, kinked hose,
intake not open, corrosion or deposits).
- Coolant leaking into exhaust.
- White smoke (doesn't rise; leaves fuel residue) = unburned fuel (didn't even ignite):
- Air in fuel.
- Low-grade fuel with poor ignition properties.
- Misfiring (low compression, defective injector, bad ignition timing).
- Very cold external air (add intake air heater).
- Water in fuel or cylinders (quenches ignition).
- Unburned engine oil in exhaust:
- Leak in oil cooler.
- Bad shaft seal on raw water pump.
- Could be fuel, not oil ?
Smoke at startup is normal; cold engine can't burn fuel completely.
Engine won't turn over,
mostly from "When Your Engine Won't Crank" article
by Harry Swieca in 6/2000 issue of Sail magazine,
some from "Servicing the Starter Motor" by Roger Hellyar-Brook:
- Shift lever in neutral ? Neutral safety switch bad ? Try moving gearshift lever back and forth.
- Breakers and battery switch set correctly ? Ignition switch correct ?
- Battery voltage okay ?
- Inspect battery terminals; clean and tighten.
- Check all big wire connections, especially ground connection. Look for any loose wires of any size.
- Check large fuse in starting ciruit.
- Label, remove, clean and re-attach wires on starter solenoid.
- Check voltages at starter solenoid:
- Large red wire should have battery voltage,
- Trip-wire S terminal (connected to ignition) should
have zero or battery voltage depending on ignition switch position.
- Check voltage at starter solenoid while cranking.
- Turn battery switch off and tap sides of solenoid and side
and end of starter motor lightly with hammer. Then try to crank engine.
- Turn battery switch on, and repeat tapping while
someone else turns ignition key on and off rapidly. Then try to crank engine.
- Make sure engine will turn over physically: put a wrench
on the crankshaft end and see it you can rotate it.
- If engine won't rotate at all, remove injectors, crank engine, and see if water
comes out of any cylinders.
- Remove the starter, check to see if teeth look mangled,
and oil its gearing (where it engages the flywheel) a little.
Starter solenoid does two things: acts as relay (activated by low current from ignition switch) to send high current
from battery into starter, and pushes gear up starter's shaft to engage flywheel.
If no click when ignition switch is turned, ignition switch circuit is bad or solenoid is stuck or failed.
If one solid click but no cranking, solenoid probably is okay, but current is weak or starter is bad or engine is seized.
If rapid clicking when ignition switch is turned, there is insufficient voltage at the starter (low battery or
From The Marine Doctor's Forum
If your starter does not work, follow these steps:
- Check the terminal of the starter motor. If there is 12 volts, the starter is faulty.
- Check the small terminal of the starter solenoid/relay. 12 volts indicates the following possibilities:
- A faulty starter solenoid/relay.
- Starter relay not grounded.
- A faulty lead wire from the solenoid/relay to the starter.
- Test the neutral safety switch (output side). 12 volts here indicates:
- A faulty lead wire from the neutral safety switch.
- Check the input side of the neutral safety switch. 12 volts here indicates:
- Gearshift not in neutral.
- Neutral safety switch not adjusted properly.
- A faulty neutral safety switch.
- Check the S (Starter) terminal on the ignition switch. 12 volts here indicates:
- Faulty wire in the harness.
- Test the B (Battery) terminal on the ignition switch. 12 volts here indicates:
NO voltage here indicates:
Less than 12 volts indicates:
- An open circuit from the Battery.
- A poor connection or a short or your battery is low or dead.
My experience with my starter motor 2/2011:
- Don't have it repaired by a guy you can't communicate with.
French-only guy in Martinique overcharged me, I don't know what he actually did, and the motor
was failing again a couple of months later.
- Research price of a new motor-and-solenoid before going to repair shop.
- No one sells rebuild kits for starter solenoids any more; buying a complete new solenoid is pretty cheap.
- Find service manuals (PDF files) online.
- Service manual for my starter motor warns: "Solenoid contacts and plunger will be
damaged if current is applied to solenoid when removed from starter motor".
Not sure exactly why that is.
There are two windings inside the solenoid, and one of them gets turned off after the
solenoid moves, so maybe that's a factor ?
- Problem eventually turned out to be in the battery and wiring.
Bought a starting battery, positioned it very close to the starter motor,
ran doubled 1/0 cables from battery directly to starter solenoid and side of
starter motor. Now the engine starts instantly.
Hard to start:
- Decompression lever or valve loose ?
- If it has glow plugs, make sure they are getting power, and voltage is good.
- If starter motor is slow, check batteries and voltage at starter motor.
- Fuel filters or injectors clogged ?
- Air leak into fuel lines ? Crank with one injector removed,
see if spray is delayed.
- If fuel problem, try starting while spraying WD-40 into air intake.
- Make sure head bolts are properly torqued.
- Carbon buildup on valves causing compression loss ?
- Worn rings causing compression loss ? Check for fuel in oil.
- Injection timing slightly off ?
- Low pressure from fuel injector pump ?
- Do compression test.
- Make sure you have water flow out the exhaust, and exhaust sounds normal.
- Make sure raw water intake seacock is open.
- Make sure raw water strainer is clear.
- Anything blocking raw water intake through-hull ?
- Low level in fresh water coolant loop ?
- Check oil level.
- Water pump belt slipping or broken ?
- Check water pump impeller.
- Air bubble in cooling system, maybe from heeling ?
- Faulty thermostat ?
- Too much antifreeze in coolant (50/50 cools better).
- Faulty temperature sensor (not really overheating) ?
- Cooling hoses constricted, crimped, kinked, blocked anywhere ?
- Corrosion or obstruction in exhaust elbow ?
- Plugged-up or slime-coated tubes in heat exchanger ?
Flush with high-pressure hose at car-wash,
or clean out with wood dowel,
or with oxalic or muriatic acid.
- Check fresh water pump.
- Air leak into water pump can make it lose its prime.
Summarized from "Keeping It Cool" by Don Casey
in 1/2001 issue of Blue Water Sailing magazine
- If runs cool, or takes too long to get to temperature: bad [or disabled] thermostat.
- If runs hot under load, but not at idle: overloaded.
- If runs hot at idle: broken pump belt, low coolant, bad thermostat, blocked circulation.
From Thomas Theisen on SailNet's Gulfstar mailing list
... We could run at about 1700 RPMs
but anything over that and we would overheat. We cleaned the heat exchanger
several times and replaced and checked the thermostat. Finally, we went
through the hoses, every rubber hose between the seacock and the exhaust
manifold. We found that several had cracks and wear that were actually
slowing the water flow. We replaced every rubber hose and this has solved
From Brian Armstrong on SailNet's Gulfstar mailing list
... had overheating problems. My
solution was to put about a pint of "lime-away" in the fresh water
cooling system and run the engine for an hour or so. The temperature
gage came right down to normal after about fifteen minutes. After a
very thorough flushing the cooling system was as good as new. I have
not had any temperature problems for the last two years.
Running too cold:
- No thermostat installed (many people remove or "punch" it to mask
an overheating problem).
- Too little antifreeze in coolant.
Sluggish / loss of power / stalling:
- Listen for engine knocking or misfiring;
could be compression or injector problem.
- Plugged-up fuel filters ?
- Water or gunk in fuel ?
- Plugged-up fuel tank vent, or crimped vent hose ?
- Plugged-up pickup tube in fuel tank, or fuel line ?
- Fouled hull or propeller ?
- Plugged-up exhaust elbow or hoses or muffler ? Flapper
valve sticking ?
- Not enough air; plugged air filter ?
- Other air-intake problems: air pre-heater not working, rebreather loop open ?
Engine quits while running:
- If just quietly shuts off, as if you hit the kill switch, maybe ran out of fuel.
- If just quietly shuts off, as if you hit the kill switch, perhaps an overheat sensor is bad,
or the stop solenoid (on injector pump) is being activated somehow.
- If engine stops with a bang, probably something stopped rotation, such as a line in the propeller.
- If RPM surges up and down before engine dies, probably fuel system problem.
RPM surges up and down:
- Fuel supply problem ? Most likely an air leak into the fuel system.
Also could be clogged filter or failing fuel pump. Or severe sloshing of fuel in tank.
Look for leaks around fuel pumps and fuel line fittings.
- Oil getting into cylinders ?
Won't go over certain RPM (but no black smoke / overloading):
- Plugged-up fuel filters ?
- Plugged-up fuel tank vent, or crimped vent hose ?
- Plugged-up pickup tube in fuel tank, or fuel line ?
- Engine compartment sound insulation.
- Valve clearance ?
- Vibration coupling on propeller shaft ?
- Idle RPM too low ?
- Is vibration the same in and out of gear ?
If so, not a shaft or propeller problem.
- One cylinder not firing, or various cylinders misfiring ?
Injector clogged ? Bad fuel ? Injector pump problems ?
- Bad or broken engine mount ?
Mount should not have rubber bulging up in center.
Nut should not be loose.
- Loose harmonic balancer on front of engine ?
- Bad propeller shaft alignment (versus transmission) ?
Observe the coupler while the engine is in gear (be careful)
to see if it is out of round.
- Bad propeller shaft or transmission bearings ?
- Bad Cutless bearing ?
Shaft shouldn't wiggle more than 1/16" at the bearing.
- Warped propeller shaft ?
With engine off and transmission in neutral, rotate shaft by hand;
shouldn't deviate by more than 1/4".
- Warped propeller ?
Remove propeller and run engine in gear. If vibration is gone,
propeller is unbalanced.
"What's Making Your Engine Vibrate?" article by Harry Swieca in 9/2001 issue of Sail magazine
Rising oil level:
- Raw water leak into oil system, through heat exchanger leak or blown gasket ?
- Transmission fluid leak into oil system, through heat exchanger leak, or gasket between engine and transmission ?
- Fuel leak into oil system, through bad injection pump, bad fuel lift pump, blown gasket, bad injector plus bad piston ring ?
- On dipstick, rust or water bubbles above oil level mark: coolant leak into oil.
- Rancid-smelling oil: engine has suffered overheating.
- Wipe oil on a white rag, look at the thin film, see a pasty abrasive soot-like
deposit: sign of blow-by from worn cylinders.
- White or emulsified oil on underside of oil filler cap: moisture in oil from head gasket of cracked block.
Water in oil:
- Bad head gasket.
- Bad exhaust elbow or siphon lock; water into exhaust port and to cylinder.
- Bad seal on water-pump shaft ?
- Bad oil cooler ? See oil in exhaust water.
- Cracked head or block.
- If oil in both fresh and seawater systems, probably blown gasket.
- if oil just in fresh water system, water pump seal.
- Look for water in cylinders. If so:
- Remove fuel injectors.
- Pump/sponge water out of cylinders.
- Turn engine over briefly (by hand if possible).
- Repeat previous two steps until no more water.
- Pour diesel into the cylinders.
- Turn engine over briefly (by hand if possible).
- Fix the leak.
- Change oil:
- Change oil and filter.
- Run engine for 15 minutes.
- Repeat previous two steps until oil is okay.
- Run engine up to normal temperature and
then run it for 30 minutes there.
Fuel leak into oil system:
- Bad injection pump lower seal, where shaft/gear from engine drives pump ?
- Bad fuel lift pump seal, where shaft/gear from engine drives pump, or main diaphragm ?
- Bad injector plus bad piston ring, dumping fuel into cylinder and then
letting it down into the crankcase ?
Don't run engine with much diesel in the oil; it thins the oil a lot and
can damage the bearings.
Loss of oil pressure:
- Oil pump problems: stuck valve inside oil pump, lost prime, etc.
- Bad oil pressure sensor or gauge.
- Sudden failure of main bearing.
Oil leak from bell housing between engine and transmission: probably means
oil leak from the main bearing seal where the drive shaft comes out of the engine. Not supposed
to be any oil inside the bell housing (on a Perkins diesel).
Black gunk in primary fuel filter
(summarized from "Feeding the Beast" by Don Casey
in Nov/Dec 2000 issue of Blue Water Sailing magazine):
- If it smells like varnish, you have old "flat" fuel: discard the fuel.
- If a couple of drops of bleach turn it white, you have algae: treat the fuel and then clean everything.
- If it dissolves in WD-40, you have tar: use the fuel until nearly empty before refueling.
From article by Steve D'Antonio in 11/2001 issue of Cruising World magazine:
- If pulley groove is highly polished, or there is belt dust
on the front of the engine, fan belt is slipping.
- Light-colored engine paint makes it easier to spot leaks.
- Oil designation: "C" means for compression engines; 2nd letter
denotes additives (higher letter is better).
- Lightly-loaded engines are harder on oil; change oil more frequently.
- Fuel: want cetane rating of 45 or higher; never go below 40.
Diagnosing fuel contamination:
- Asphalt: looks like tar, dissolves in WD-40.
- Biological growth: turns white when sprayed with bleach.
From "Oil Test" article by Larry Blais in issue 2003 #3 of DIY Boat Owner magazine:
Reading results of engine oil analysis:
- Aluminum: should be 15 PPM or less. Usually comes from pistons, maybe crankshaft or camshaft bearings.
- Chromium: should be 15 PPM or less. Usually comes from piston rings, and ball/roller bearings.
- Copper: should be 25 PPM or less. Usually comes from oil cooler.
- Iron: should be 100 PPM or less. Usually comes from cylinder liners, piston rings, oil pump.
- Lead: should be 25 PPM or less. Usually comes from main, rod or camshaft bearings.
- Molybdenum: should be trace amounts. Usually comes from top piston ring.
- Silicon: should be 15 PPM or less, unless oil contains it as an additive.
- Sodium: indicates coolant or wet exhaust leak, unless oil contains it as an additive.
- Tin: should be 15 PPM or less. Usually comes from main, rod or camshaft bearings.
- Zinc: common oil additive; better oil may have 1000 PPM or more.
- Rate of soot accumulation in oil indicates quality of combustion. More soot means
bad combustion, and degrades oil effectiveness.
- Oxidation and nitration: increase over life of the oil. If high, caused by too long between
oil changes, or overheating.
- Sulfonation: low TBN and high TAN mean too acidic, from low operating temperature or lots of idling.
- Water: could be from low operating temperature, as well as a leak.
Also can test coolant, hydraulic fluid, transmission fluid.
From Al Herrle on SailNet's Gulfstar mailing list:
I have a Perkins 6-354 with compression at 320 psi, 420, 415, 270, 380, and 400 for
cylinders one thru six respectively. The mechanic suggests that a valve job
be conducted at a cost of approximately $1500. If that fails to address the
compression problem, they further recommend removing the block and repairing
as necessary. They suggested that the cost of this venture could exceed
From Roland Storbeck on SailNet's Gulfstar mailing list:
The compression problem is going to be either the valves or blow-by at the
rings. Try this: squirt a little lube oil into each cylinder (I find that 80
weight gear oil works the best). Repeat the compression test. The oil
will substantially help seal the rings, so if your compression improves a lot
then your problem is the expensive rebuild. If the compression only improves
a little, then you're looking at the valve job.
On underside of coolant filler cap, slimy white paste or very dark coolant:
exhaust gasses are getting into the cooling system.
Jim Kerr's "Fuel Injector Cleaning"
Injection pump service / injector service:
Blue Ridge Diesel Injection
Foley Marine (a pain to work with)
Fred Holmes Fuel Injection (Canada)
J & H Diesel Service
Jobbersinc (best pump price I found)
Real Diesel (888-349-9461)
When sending injectors out to be serviced, do not send washers with injectors.
My injectors came back without the washers, and I had a difficult time getting
From Gordon Endler, and consensus of others:
[When replacing fuel injection pump on my Perkins 6.354, I asked if
getting the timing wrong could damage the engine, injectors, fuel lines
or injector pump.]
If your pump timing is out it will not damage your engine.
Depending on how far it is out, it will either not start at all, or if just out
the engine will have no power and be hard to start. Might smoke as well, but
you can not damage the engine; it is only if you get the valve timing out that you can damage the engine.
Fuel line thread sealants: Rectorseal #5; Whitlam TU-555 Thread Sealing Compound.
Gunk/growth in fuel tank:
Summarized from Steve Wolfe in 4/2005 issue of Sail magazine:
Algae doesn't grow in diesel; bacteria, fungi and yeast
can grow in the water in the tank and tolerate diesel.
Some eat the hydrocarbons in diesel and produce sludge.
Others eat the sulfur in the fuel.
Keeping water out of the tank will prevent most growth.
Magnets don't work to destroy growth; if they did,
every sewage plant in the world would use them.
From TTollef552 on the Morgan mailing list
I had a similar problem in the Bahamas far from tank cleaning services.
What I did was remove the tank access lid, use the dinghy hand-pump to draw
the fuel off the tank bottom where the microbes exist and into a bucket.
When the bucket was full, I would pump the fuel back into the tank through
clean rags and shop towels. We did this pumping for three hours on each 35
gallon fuel tank. Then I would change out the Racor filter element. The engine
mounted spin-on filter did not need change-out every time as the Racor
primary blocked most of the grit. I would recommend a supply of a dozen fuel
filter elements of each type on board until the contamination problem cleans
up. And lots of toweling in your engine supply stores.
An amazing number of black grit (dead critters ?) were captured by the
improvised rag filters. This method worked, cleaning up the fuel adequately;
the filter blockage went from every three hours to twenty-five hours. Filter
changes were necessary all the way home. Now the interval is back to a
hundred hours after tank cleaning by fuel extraction, filtration, tank
scouring under fuel pressure and scraping behind the fuel baffles. The
latter scouring behind the baffles was very important;
fuel cleaning services usually avoid this time-consuming effort. You
should also change out the fuel tank access lid gasket (hardware store item)
before you close up the tank.
Water in fuel tank:
From John / Truelove on the IRBS live-aboard mailing list:
I suggest that if you have water in your fuel tank, the best solution is to
remove it. Using alcohol [additive] in the fuel may damage your injection pump and
injectors. Properly designed tanks will have a "low spot" in the bottom and
an ullage opening (for a sounding rod) in the access plate. If so, you can
use a handy-billy pump like the ones used for oil changing to withdraw the
water. Otherwise, pull the access plate, pump the fuel off the top and then
pump the water out. You can use water-finder paste to find where the
interface is. This latter method should be done every few years anyway; while
you're at it, you'll find yourself looking at all those "hidden" things like
fuel hoses which really ought to be looked at more often. When you're done,
the tank should be completely wiped out and dried. You may be surprised at
what you'll find in there.
When you're finished, you'll rest easy with the knowledge that you won't get
caught changing fuel filters while in a bad spot on a stormy night. That
peace of mind, IMHO, is worth even many days work.
From Mike Toledano on Cruising World message board:
My experience has been that rebuilds on old diesels are pretty much
a waste of money and time - unless you do all the labor yourself (and
know what you're doing). The cost and trouble of getting the old
engine out and putting it back in again, plus the labor and parts
on the rebuild, in my experience, are usually a very large
percentage (70% ?) of the cost of a new engine.
From "Installing a New Auxiliary" article by Don Casey in 4/2001 issue of Sail magazine:
One gallon of diesel fuel will produce around 16 HP for 1 hour.
So the average load on a diesel engine can be estimated by multiplying
fuel consumption (in gallons per hour) by 16.
David Pascoe's "Drive System Alignment"
"Do It Yourself Engine Alignment" article by Don Casey
in 6/2001 issue of Blue Water Sailing magazine.
Jack Harden's "Get In Line"
From "Do It Yourself Engine Alignment" article by Don Casey
in 6/2001 issue of Blue Water Sailing magazine:
My idea: after checking and fixing alignment, I would run engine a bit and then
check alignment again. Repeat until no fixing is needed.
- Misalignment puts strain on shaft and transmission seal and cutless bearing, and
- Should check alignment once a year.
- Do alignment with boat in water.
- Check condition of engine mounts before checking alignment.
- To check alignment:
- Pencil or punch marks on two halves of shaft coupling, so you
can put them back together the same way.
- Loosen or remove bolts on shaft coupling.
- Use feeler gauge to measure gaps between halves on the coupling ("face alignment"),
at top, bottom, port, starboard. Want differences no more than .001" per inch of flange diameter.
- Rotate coupling halves 180 degrees relative to each other, and check
again. If numbers are different, flange is crooked on the shaft ("flange run-out"), and
must be fixed before fixing rest of alignment.
- Lay a straightedge fore-and-aft across the shaft coupling to
see if two lengths of the shaft are in line ("bore alignment").
Check alignment from top and from side.
Tough to do, because prop shaft will sag with bolts out.
Maybe leave bolts in but loose ? Or support shaft with a rope,
letting it assume natural direction from cutless bearing ?
- Typically, each engine mount has three nuts on the vertical stud: two locknuts,
and a jacknut between them.
- Engine position is adjusted in two ways: moving jacknuts to move engine corners up or down,
and loosening engine-bed bolts and banging mounts with a mallet
to move engine corners sideways.
- Vertical adjustment: adjust jacknuts 1/4 turn at a time.
- Sideways adjustment: trace around mounts before loosening them, to record
starting positions. Use a mallet, bottle jack, come-along or turnbuckle to move
the loosened mounts (not directly on the engine).
- When fixing face alignment, adjust forward mounts first.
Adjusting aft mounts tends to change bore alignment.
- Alternate between checking and fixing face and bore alignment
until both are correct.
- After tightening engine mount nuts and bolts, check alignments again.
If off, try releasing top nuts one at a time to see if one is affecting
Replacing engine mounts:
- You replace the whole
mount, not just the rubber insert (which probably is pressed in).
- Do with boat in the water, and not right after a haulout.
Want normal hull loading and shape.
- Probably need to support engine, even if removing
only one mount at a time.
- Best to replace them all at same time, but not
- Big job: re-aligning the transmission output
shaft flange and prop shaft's flange.
Need feeler gauge.
May have to do it multiple times as new mounts get
"broken in" over time.
- May be able to get away without disconnecting hoses
and wires, if there is enough slack in them.
- Usual problems: rusted/frozen bolts.
- Could use a come-along or chain hoist to raise/support/move engine.
Requires an overhead attachment point.
- Could use a hydraulic ram to raise/support/move engine.
Maybe "power pac" or "Enerpac" used by body shops for car straightening.
But expensive and you may not be able to rent.
- Could use hydraulic jack ($130 at
Northern Tool and Equipment)
and manual Hydraulic Ram Pump ($43 at Northern).
- Could use Adjustable Stubby Hydraulic Bottle Jack ($35 at
Northern Tool and Equipment).
Room to swing handle ?
- Could use a car jack (if room for upright, and room to swing handle).
- Someone told me a cautionary tale: someone noticed huge vibration of their small
(1-cylinder, 2-cylinder ?) diesel, so replaced the engine mounts.
That resulted in horrible vibration being transmitted into the entire hull,
vibrating the whole boat. So they put the old mounts back in.
From Lew Hodgett on The Live-Aboard List:
After having gone thru several engine mount change-outs because my Yanmar
YSM12 could snap 3/4-16 engine mount studs like they were old pretzels, I
found the Aqua-Drive and installed it.
The Aqua-drive is basically a CV joint that allows the engine to bounce
around freely on soft rubber mounts and definitely does not require, even
want, engine-shaft alignment.
After installation, the noise level dropped at least 25 dB, screws quit
backing out of things because the vibration was reduced, and it quit
snapping engine mount studs.
Without question, the boat I'm building will have one.
IMHO, it is the best money you will ever spend.
From Roger Rippy on The Live-Aboard List:
Having never tackled motor-mount replacement before, I was a little apprehensive.
But looking back on the project, it was a piece of cake!
First thing I did was borrow a small hydraulic lift kit that contained
several different types of expansion lifts that attached to a hydraulic hand
pump by a 3-foot hose. This really made it easy. I then
sprung for all 4 motor-mounts ($400). I figured if one
was bad, they probably were all on their last legs.
I then carefully measured
the clearances and adjustments on the existing mounts, since the motor was
fairly well aligned. I disconnected the shaft coupler, took off the top lock
nuts from the old mounts, and jacked up one mount at a time and replaced it
with a new one. I set the lower adjustment nut to the clearance of the old
one on each of the mounts. The hydraulic lifts helped because there is not a
lot of working room around an auxiliary on a Bristol 31.1 !
the mounts, I reconnected the shaft coupler and used a pry bar to get the
alignment close and then I proceeded to align the couplers using a feeler
gauge and a little patience. I am glad that this project is over!
Replacing head gasket, from Gary Elder:
One of the biggest risks is breaking a head bolt or a
head stud (I don't know which you have). If that happens, removing the
'remains' can be a bit intimidating. I've had it happen to me, and I had to
drill out the broken portion of the bolts - with a hand-held electric drill,
without damaging the female threads in the block.
Another consideration is cleanliness. All the crud that can fall into the
cylinders when you remove the head and gasket must be removed before you
install the new gasket and head. Sometimes small pieces of 'carbon', or even
gasket material, will fall between the piston and cylinder wall, above the
top ring - ya gotta remove that crud before the head goes back on. Don't
let any seawater get into the cylinders either.
Also, you will need a torque wrench, probably in the range of 75 - 150 ft
lbs. They can be rented from the better equipment rental companies. You
will need to find out what the actual torque specs are, and the tightening
sequence for YOUR engine.
When removing the head and/or valves, don't mix components;
keep the valves, rocker arms and push-rods sorted out in
matching sets. That way, you won't have to adjust the valve
clearances (much) after reassembling them.
Removing gaskets, in general, from NAPA Auto bulletin:
- Older engines are made of cast iron and steel; you can be very aggressive
when removing gasket remnants from surfaces. Newer engines use a lot of aluminum
and plastic; you have to be more careful. Power-grinding or aggressive scraping
can damage a surface; using a proper gasket-scraper tool, or spray gasket-solvent,
- Older engines typically used cork/rubber gaskets to seal valve covers,
oil pans and timing covers. Intake manifolds used fiber or metal gaskets.
Head gaskets were embossed steel or fiber-faced composition.
Newer engines often use cored or multi-layer gaskets, silicone rubber, or just sealant.
Multi-layered head gaskets can require very fine tolerances on the mating surfaces.
- Follow recommendations on whether to add sealant to a gasket when installing it.
In general, sealant can be used with cork/rubber, fiber or paper gaskets,
and not with molded rubber, soft-faced or coated head gaskets.
- Some sealants interfere with oxygen sensors on newer engines;
use a "low volatile" sealant instead.
Dealing with a seized engine (seized because of rust/disuse):
From Arild Jensen on The Live-Aboard List:
... Remove the injectors, pour penetrating oil into the cylinders and let it seep in.
Refill every few days as necessary.
[Try] to slowly force the crank over by applying a four-foot bar
bolted to the flywheel.
Repeated applications of penetrating oil and continual movement
may eventually free up the pistons
The worst thing you can do is try and rush it, or try and run
the engine as soon as you free up
the pistons. If you can free the pistons, continue to turn
over the engine by hand, while
adding lubricating oil.
This will help minimize the amount of scoring to the cylinder walls.
It will also minimize the possibility of breaking the rings
while they are still in the piston
If you do find actual water in one or more cylinders,
first try and suck up the water with a thin
plastic tube, then use something like WD-40 which does displace water. Fill those
Don't let air in to sit and allow more rusting.
Patience and perserverance could well save you a bundle of $$$ and an engine.
From Mark Mech on The Live-Aboard List:
If you can free it up with Kroil or some other penetrating oil, turn it over
a few times, then fill each cylinder and suck out the oil to remove some of
Once you start and run the engine you will need to run it for a while to see
if the rings re-seat.
If the compression is still weak after couple hours of run time, you can try
this next step.
This sounds radical, but it works on engines with poor compression due to
You mix some Bon Ami with water and slowly pour it down the air intake or
carburetor while reving the engine.
It is slightly abrasive and will polish the rings and cylinders together
without scoring anything.
Repeat the process several times and check the compression again.
Jesse Brett's "Replace Diesel Engine"
From SC Seaside on SailNet's Gulfstar mailing list:
I've been a mechanic for 40+ years and any first-rate mechanic should be able
to tell you whether your problem is a valve job or a complete rebuild. A
previous writer suggested using a heavy gear oil to test your compression and
this usually produces a pretty good result. Expect to smoke up the yard/marina a
lot when your fire the engine back up. As previously stated, if the
compression improves dramatically with the oil in the cylinder, you need a
I have a Ford 120 in my Gulfstar 43 MS and we rebuilt her bottom to top without removing
the engine from the boat.
We removed the head and had it reworked at a local machine shop. This
included replacing all valve springs, valve guides, milling the head, and
grinding and reseating the valves. Total cost, $750.
New injectors, $420.
I purchased a new crankshaft, main and rod bearings, new compression and
wiper rings, and honed all cylinders. Total cost $680. We reused all
pistons, pins, and connecting rods.
Water pump $65.
Gasget set, $125.
Misc clamps and hoses, $25.
Of course we did all the labor, which is the main cost associated with this
undertaking, but she now purrs like a kitten and at a fraction of the cost
of a new engine or having to pay outrageous labor charges. Not to mention
ripping out the cockpit floor.
If you've got as much room around your engine as I have around mine, I would
suggest you entertain bids from local diesel mechanics to rebuild her where
she sits, if that's what is needed. Be sure and put plenty of absorbent in
your bilge and change it regularly, seal off the engine room as much as possible
to prevent smelling up your cabin and vent, vent, vent. We did the project
over the winter and even with the cold outside, it got pretty steamy in the
confines of the engine room at times.
From BMW Touring on SailNet's Gulfstar mailing list:
We have a Gulfstar 50 MkII. I had the Perkins
removed by means of
a cable lowered into the engine room which is attached to the engine lifting
lugs using a lifting bar.
This is done via the round access plate put there for that purpose just
forward of the steering pedestal.
The engine/transmission are unhooked from everything, then lifted and slid
forward into the companionway using timbers placed under the mounts and a
come-along. The engine is removed
from the boat straight up by a crane and that's it.
Personally, after having gone through all of this - I think an in-boat
rebuild is the way to go.
From Arild Jensen on The Live-Aboard List:
Re: hoisting engine: A word of caution.
Slinging any load from the boom which is supported by a halyard to the masthead
will create an effect similar to having that same weight suspended from the
This will cause a lot of heeling.
Because you have removed the engine from the hull you no longer have that
ballast effect to assist with righting moment.
Therefore the heeling amount will greatly increase.
My recommendation would be to use a gin pole crane or else a tractor with a
bucket or similar to lift the engine from boat to shore.
The last thing you need is a stability issue dropping the engine overboard at
the last moment.
How much can it cost to have the yard guy help with the tractor for half an hour?
From Mike on World-Cruising mailing list:
Re: Repowering a Cruising Sailboat:
One caution for replacing an Atomic 4, it is important to
keep the same prop rotation direction. Many boats have the
prop shaft at an angle to counteract prop steer; if you
reverse the rotation with a new engine and transmission
the boat may not want to steer properly under power.
Jury-rigging coolant system, from "Bypassing a Raw-Water Pump" article by Patrick Childress in 11/2001 issue of Sail magazine:
- Substituting with a bilge pump: bilge or wash-down or drinking-water pumps may overheat if run continuously.
- Engine raw-water pump flow varies with engine RPM, so may have to adjust engine
RPM to match flow of substitute pump.
- 3 GPM pump worked okay to replace raw-water pump; some engine raw-water pumps
move 10 GPM at 1800 RPM.
- Flow of fresh-water pump is much lower than that of raw-water pump.
And many pumps can't stand the higher temperatures in the fresh-water loop.
- If fresh-water pump fails, remove thermostat to improve flow.
From Brett in Benner Bay:
If leak from fresh water (antifreeze) coolant system into oil system, drain both systems
and refill both with oil (lightest possible is best in coolant system). Engine will
run a bit hot, but leak will now be harmless.
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