When a new outboard engine is being broken in, the continuous utilization of full power should be avoided for the initial five to ten hours of operation. Full throttle operation should be increased gradually to afford moving parts the opportunity to seat themselves. The following operation schedule is recommended to break in two cylinder outboards that are rated up to 35 horsepower:

First hour: you should operate the engine at its lowest speed for a minimum of fifteen minutes; thereafter, operate the motor at full throttle for brief periods of up to 1 ½ minutes, leaving intervals of from five to ten minutes between each.

Second hour: increase the duration of full throttle bursts to from 2 to 3 minutes; between bursts of full throttle operation, slow the engine to half throttle to allow it time for cooling.

After second hour: full throttle operation may be increased, but you should still avoid continuous use of maximum power for lengthy periods for the next three hours. Consult your engine service manual to unearth further operating restrictions.

During the break in period of an engine, you should periodically check the operation of the cooling system to ensure that it is functioning properly, and that the engine being seated is no danger of overheating. Check the overboard indicator located at the rear exhaust housing just below the powerhead. If this overboard indicator is discharging water, it indicates that the cooling system is operating properly. However not all engines are so equipped. Some contain temperature sensitive devices in their cylinder heads. This feature guarantees that if engine temperatures ever rise beyond their maximum safe levels, switches will close and a warning horn will sound in the control box.


In most areas of North America, the climate allows for outboard engine use just part of the year. During the off season, engines must be stored; this storage period may be as lengthy as ten months. Before an outboard is stored, steps must be taken to prevent deterioration and the formation of rust. Particular attention must be paid to the cylinders, the pistons, and the cooling system.

To prevent rust from forming on pistons and cylinder walls, the cylinders should be protected with either a coating of engine oil or rust preventing compound. Remove the engine spark plugs, and pour a small quantity of engine oil or compound into each cylinder. Then turn over the engine by hand, using its recoil rope, several times to evenly distribute the fluid.

To protect the crankcase, crankshaft, carburetor and intake manifold, and leaf valves, outboards should be fogged before storage. In fogging, a rust preventing compound is sprayed into the carburetor intake, or into a special fogging hole which some engine models possess, while the engine runs. Fogging is continued until the engine stalls or begins to smoke excessively.

If an outboard contains a built in fuel tank, it should be drained. Then check the fuel lines and fuel filter, cleaning them if necessary. If the engine utilizes a remote tank, the tank can either be emptied before storage, or the fuel treated with a stabilizer which gives standard gasoline a life span of up to one year.

Next, the cooling system should be drained. The system should also be flushed if the engine was used in salt water or in silty conditions. Drain and flush the lower unit, then refill its gearcase with the proper lubricant.

Now you can remove the propeller and grease its shaft thoroughly. Lubricate the engine as described in WHAT SHOULD BE DONE IN AN OUTBOARD TUNEUP. Apply a coating of automotive wax to the exterior of the lower engine cover and exhaust housing. Finally, place the engine in upright position in a dry well ventilated area for storage.

When you remove the engine from storage to prepare it for use, thoroughly inspect it for worn or damaged parts, leaky gearcase seals, and loose screws. After the engine is started, check the operation of the cooling system to make certain that the water pump has not seized. Before returning the engine to regular service, perform a thorough tune up as detailed in WHAT SHOULD BE DONE IN AN OUTBOARD TUNEUP.


If you discover a mechanical problem in the powerhead, the powerhead will need to be removed and disassembled, cleaned, and then repaired before it is reassembled. As a general rule, to remove a powerhead from its engine exhaust housing, you should disconnect the following components first(remember that these are general procedures which apply to most outboards; for information about a particular engine, always consult its service manual):

1)The fuel tank(if the tank is powerhead mounted)

2)The carburetor(s)

3)The intake manifold and leaf valve assembly

4)The fuel pump and fuel lines

5)The flywheel and armature plate

6)The power pack(s), and ignition coils

7)Spark plugs

8)The starter(or starter motor and its solenoid)

On some larger engines, to reduce powerhead weight, the cylinder heads and exhaust covers should also be removed.

After these components have been removed from the powerhead, the powerhead itself can be disconnected from the exhaust housing. This may involve removing part of the lower engine cover for appropriate access to the powerhead mounting screws. The powerhead mounting screws are often located near the base of the manual steering arm or steering linkage. Remove the powerhead mounting screws, then lift the powerhead off of the engine exhaust housing. Larger engines may require the use of a hoist for powerhead removal. When you are placing the powerhead on your workbench, be careful not to damage or bend the inner exhaust tube. Studs in the powerhead can be protected from damage by screwing a nut over each, and tightening it until it is flush with the end of the stud.

Once the powerhead is safely aboard a workbench, you can begin the disassembly and inspection process. Powerhead disassembly is normally a straightforward procedure. Detailed instructions for it will be provided in most engine service manuals. Most manuals will also contain exploded diagrams which identify all engine parts. These can be extremely helpful when disassembling and reassembling an engine.

Some repairs may not require that you completely disassemble the engine powerhead. Upper and lower main crankshaft seals, for instance, can usually be replaced absent powerhead disassembly. Replacement of the upper crankshaft seal often will not even require powerhead removal. However any time that you need to service the cylinder or pistons, the powerhead must be completely disassembled.

When disassembling the engine, it is a good idea to have several clean, covered containers available that can be used to hold and organize small parts like fasteners and bearings. For example, you may wish to use a separate container for the parts of each powerhead area. Parts should always be replaced in the exact location from which they were removed. This is especially true of moving parts, such as needle bearings and connecting rod caps. It is also important to tag or identify larger parts as engine disassembly occurs. You can try using a grease pencil to mark the cylinder number on each piston so that you know exactly where it should be reinstalled. Connecting rods should be tagged so that they can be reassembled with the correct piston. To prevent larger parts from becoming contaminated with dirt or old oil, always keep a work area as clean as possible.

You should begin powerhead disassembly by removing the cylinder head or heads, and the exhaust cover covers(if they had not been removed earlier). If the pistons must be removed, the crankcase will need to come off first to allow access to the connecting rod caps. Be careful to protect the crankcase gasket surfaces and cylinder block from damage. Usually there will not be a gasket placed between the cylinder block and crankcase.

When the powerhead is disassembled, you will need to clean its components with solvent, and blow them dry with compressed air. Pay attention to the cleaning of oil and water passages. When all parts have been cleaned, inspect them for wear and damage. If components show damage or extraordinary wear, try to identify the source of the mechanical problem that fostered it. Below is a general procedure that can be used to inspect and rebuild powerhead components:

1)Inspect the cylinder walls for scoring and scuffing; then measure their roundness and taper, and compare these measurements to service manual specifications

2)Deglaze the cylinder or cylinders with a honing tool. If necessary, resize the cylinders so that they meet specifications

3)After the cylinders have been deglazed or resized, clean the cylinder block with soap and water; then clean the block again with solvent, and blow it dry with compressed air

4)Check the exhaust ports for an excess of carbon deposits; scrape away any carbon deposits which are found. Even a sliver of carbon buildup can interfere with proper exhaust flow

5)Check the piston or pistons for wear, and verify that their rings are not sticking as a result of carbon accumulation. Clean all petroleum gum and varnish deposits from the pistons with cleaning solvent; carefully scrape any carbon deposits from the piston tops

6)Measure the pistons and compare your measurements to the service manual specifications(PISTON)

7)Install new rings on each piston

8)Clean and inspect the crankshaft and crankcase bearings. Bearings that exhibit signs of corrosion, wear, or undue discoloration should be replaced

When all parts have been cleaned and serviced, you can reassemble the powerhead. Always employ new gaskets during reassembly; remember to thoroughly clean any old gasket residue and cement from the gasket surfaces. Unless otherwise specified by a gasket manufacturer, lightly coat both sides of gaskets with gasket sealing compound before installation.

Before the cylinder head is reinstalled, it should be resurfaced to remove any high spots from the gasket face. Then the cylinder head can be reinstalled with a new gasket. As before, lightly coat both sides of the gasket with gasket sealing compound unless the gasket manufacturer specifies otherwise. Cylinder head bolts should be tightened in their recommended sequence, and to the proper torque value.

Once you have identified and repaired its mechanical problem, and reassembled the powerhead, the engine should be tested, either inside a tank or on a boat. Following the test, wait until the engine has cooled, then retorque all cylinder head bolts, observing their proper sequence. Whenever the powerhead has been disassembled and serviced, the engine must also be broken in as if new(see the procedure described above).


Outboard engine overheating is commonly caused by a faulty water pump. To service an outboard water pump, you will need to remove the gearcase from the exhaust housing. Gearcase removal does not require removal of the powerhead. The ignition system should be disabled to prevent accidental starting. If you are working with an electric start, the battery should also be disconnected to prevent accidental engagement of the starter motor.

The procedure utilized to remove and service the water pump will vary by engine model, however the removal procedure described here can be applied to the water pumps of most outboard engines. You should carefully follow service manual instructions when you are removing the gearcase.

Consider the gearcase and hardware of a typical 35 horsepower two cylinder engine. Before you can remove the screws and nuts that secure the gearcase in place, you must remove both the port and starboard side water intake screens to access the shift rod connector. Removing the keeper and upper connector from the upper shift rod will enable the gearcase to be lowered.

As you lower the gearcase from the midsection, be careful not to damage the driveshaft as it emerges from the exhaust housing. Depending on engine model, the water tube that connects the water pump to the powerhead may come away with the gearcase.

Disassembling an outboard water pump is a simple matter of removing the water tube and water tube grommet, then removing the screws that secure the impeller housing. The water pump housing can then be lifted over the driveshaft end and removed from the engine. When the water pump is removed, you should be able to remove the impeller by lifting it too over the driveshaft end. Unless the impeller pin is damaged, it should be saved. The gasket that lies between the water pump housing and impeller plate, and the gasket that lies between the impeller plate and gearcase, should both be discarded.

Next, inspect the impeller, the impeller housing, the cup, and the impeller plate for wear, damage, and corrosion. Replace these parts as necessary. If the impeller housing seal leaks, allowing water to escape from the pump chamber and thereby negatively affecting pump pressure, the seal needs to be replaced. To install a new impeller housing seal, you will need a special tool of the same diameter as the seal, the end of which will contact the entire seal surface as it is driven into place. Use such a tool by placing the housing upside down on a wooden block that has a ¾ inches diameter hole cut into it. This hole will accept the end of the tool as it seats the seal.

To reassemble the water pump, apply a light coating of gasket sealing compound to both sides of the new impeller plate gaskets. These gaskets are not interchangeable; they must be installed in their proper positions for the pump to function acceptably. Install the gaskets, then apply a dab of needle bearing grease to hold the impeller pin in position on the driveshaft, and slide the impeller into place.

Insert the new water tube grommet into the water outlet on the impeller housing. If the impeller cup was removed from the housing for replacement of the seal, reinstall it in the housing now. Then slide the housing over the driveshaft end and down the driveshaft. Before you fit the housing over the impeller, apply a smidge of oil to each impeller blade tip. Slowly rotate the driveshaft in a clockwise direction as you are lowering the housing over the impeller. This will ensure that the impeller blades are suitably positioned in the housing. Next, tighten the impeller housing screws, and install the water tube in the grommet in pump outlet; finally, reinstall the gearcase on the exhaust housing.


The most common symptom of a gearcase problem is excessive noise. Excessive noise can be caused by several conditions. If either the seals or plugs are faulty, lubricant will be lost, and the resulting inadequate lubrication of the gears will create noise. Contaminants like metal particles or water in the lubricant will cause noise, and greatly accelerate gearcase component wear. If you discover metal particles or water in a lubricant, you will need to disassemble the gearcase, and check its components for wear and damage.

A gearcase pressure test will reveal leaking seals. A vacuum test of the gearcase may also be advisable, particularly if the noise problem relates to water in the gearcase. To perform a gearcase vacuum test, you must drain the gearcase, and attach a gearcase vacuum tester to the drain opening. Then reduce the internal pressure inside the gearcase until the test gauge reads between three and five inches of mercury. Watch the gauge for few seconds; the mercury reading should remain the same. If the reading drops, then the gearcase is losing pressure. If the gearcase retains only partial vacuum, reduce the internal pressure further, so that the test gauge reads 15 inches of mercury. If the gearcase can still retain its partial vacuum, then the seals are okay. If the pressure reading drops, the seals are leaking.

To locate the leak in a seal, spread a little bit of oil around the seal perimeter. Apply the oil to one seal at a time, then repeat the vacuum test and observe the oil. If the oil is being drawn into the gearcase in any location during the test, that seal is faulty. Check all seals in this same manner. To remove and replace a leaky driveshaft seal, the water pump and gearcase cover often must be removed. The propeller must be removed if you need to replace the propeller shaft seals.

Noise in the gearcase may also be caused by problems in the right angle drive components. Although the operation of the right angle drive is virtually identical in all engines, gearcase housings will vary by engine model, impacting the way that the gearcase is disassembled.

For example, the gearcase in a small outboard engine will usually be cast in a single piece. This is also true when an engine exhaust outlets are located in its propeller hub. When a gearcase is cast in a single piece, the right angle drive components will need to be removed from the gearcase one by one. In other engines, the gearcase is made in two parts. In this type of gearcase arrangement, after its lower section has been removed, you can simply lift the propeller shaft out of its upper section. The bearing head, bevel gears, clutch dog, and front bearing will all remain on the propeller shaft; likewise the shift lever will remain attached to the shift rod.

If you suspect a problem in the right angle drive components, first remove the gearcase. Then inspect the gearcase exterior for damage. A bent, dented, or cracked gearcase must be replaced. Next remove the propeller, and disassemble the propeller shaft components on your workbench. Note that special tools are required to pull or drive out driveshaft seals and bearings, pinion gear bearings, and shift rod bushings.

Now thoroughly clean all gearcase parts, including the drive gear components, the propeller shaft, the driveshaft, and the bearings and retainers. Then blow these components dry with compressed air. All old oil seals, O rings, and gaskets that were removed from the gearcase should be discarded.

Inspect all drive gear components carefully for wear or damage, paying particular attention to the upper and lower driveshaft splines. If these parts are badly worn, the entire lower unit may be bent out of alignment, perhaps the result of contact with a submerged object. Be aware that if the upper driveshaft splines are damaged, the crankshaft splines are probably also damaged. If the crankshaft splines are damaged, the powerhead will need to be removed, and a new crankshaft installed.

Remove the exhaust housing, and check it for damage and straightness. Check the forward and reverse drive gears, and the clutch dog carefully. If the engagement surfaces of the clutch dog or the drive gears are chipped or rounded off, it reveals that an operator is likely and repeatedly shifting gears at an excessive rpm. Replace the parts as necessary.

The contact surfaces between the gearcase and the exhaust housing should be checked for nicks, scratches, and distortions. If the engine has a two piece gearcase, check between the gearcase halves for wear and damage. Minor irregularities on the contact surfaces can be removed by resurfacing the affected area (just as the cylinder head gasket surfaces would be refinished)(GASKET). However if the surfaces are severely marred, the component must be replaced.

After all of the components are cleaned, inspected, and replaced as necessary, you can reassemble the gearcase. Never force together any assemblies when a gearcase is being reassembled. Components that are designed to fit together should do so smoothly and easily, unless press fits are specifically instructed by an engine service manual. Lightly coat the oil seals with gasket sealing compound before they are installed. Always use new gaskets and O rings. Consult the engine service manual to learn the correct torque values for various fasteners. After the gearcase is reassembled, but prior to its being reinstalled on the exhaust housing, it should be both pressure and vacuum tested to be certain that it is sealing properly. Then the gearcase can be reattached to the engine.


An engine is said to be binding when it is difficult or impossible to turn over. An engine flywheel should always turn smoothly, and with minimum resistance. There should be a modest resistance only when the piston reaches and passes top dead center(TDC). If, when the engine is tested, it appears to be binding, you should never use force to turn it over. This can damage its internal parts.

Binding can result from sundry conditions. The most common of these is mechanical damage in either the gearcase or powerhead. Broken piston rings, or damaged connecting rod or crankshaft bearings are typical powerhead problems that will induce binding. Binding can also occur if the piston rings are too large for a cylinder, if the incorrect rings were installed during a cylinder head rebuild for instance.


The most common cause of outboard engine vibration is a damaged propeller. Therefore, to solve a vibration problem, first examine its propeller for bends, cracks, or breaks in the blades, and replace if necessary. You should never attempt to repair a cracked or broken blade by welding it. You can remove minor nicks in a blade by filing, however if you do file out a nick, be careful to retain the original shape of the blade edge which is a prerequisite for proper water movement during operation. Also, you should avoid removing too much metal because this can cause the blades to become unbalanced. For this reason, badly nicked propellers cannot be treated, and instead must be replaced.

Another cause of engine vibration is loose or worn rubber isolation mounts. An outboard engine contains a number of rubber mounts to isolate its exhaust housing from the stern bracket. The rubber mounts absorb engine vibrations, preventing them from reaching boat occupants through the transom. A typical 25 or 35 horsepower engine has six mounts, two of them upper side mounts, two of them lower side mounts, one an upper thrust mount immediately below the powerhead, and the last a lower thrust mount between the exhaust housing and lower stern bracket.

To inspect the lower thrust and side mounts, remove the cover plates. Depending on the engine, you may need to remove the powerhead, and lower the engine cover to inspect these particular mounts. Any loose mounts should be tightened; worn mounts should be replaced.