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Outboard Engine Servicing

After your engine has been properly run in, you will need to determine a maintenance routine that begins with systematic checks every time you use your boat. These checks won’t take long, but could spell the difference between life and death to your engine.

Daily Checks and Outboard Maintenance

Daily checks should include a fast look at just some key items. First, make sure that your oil tank (when you have one) is topped up. You probably have a four-stroke engine, make sure you check the crankcase-oil level and top up if needed. Check your owner’s manual to find out if your dipstick must be screwed in, or left unthreaded once you check the oil level. Failure to take action could give you a false reading, and lead to overfilling or underfilling your engine’s crankcase, which may cause problems.

Check that you’ve got adequate fuel on your intended trip, and that the fuel-tank vent is open.
With the engine tilted up, check for excess oil buildup near your propeller…it could mean that a seal in your lower gearcase has deteriorated. (Note: Some oil film buildup is normal in lots of cases; search for changes in the amount of buildup. If it appears to be increasing, check the oil level within the lower unit as discussed in the owner’s manual) If the seal has failed, take the engine to an engine repair shop immediately to avoid expensive gear-unit damage.

Check for fishing line wrapped around the propeller hub area. In the event you ignore it, the line can wrap tightly across the propshaft and cause the aforementioned gearcase seal failure.

If your engine shouldn’t be through-bolted to the transom of your boat, be sure the screw clamps are tight and secure. Many engines have landed on the bottom of the sea through neglect of this simple check.

Sniff around for any sign of a fuel leak, and if you discover one, fix it.

Once the engine is running, make sure that to check the “telltale,” or “tracer,” spray, or exhaust discharge, to make certain the water pump is working.

If all these items are in order, you are ready to go. There’s just yet one more thing:

For those who tow your boat on a trailer, and run it in salt water, flush the cooling system daily with fresh water.

Monthly Checks and Outboard Maintenance

On a monthly basis, besides the routine daily checks, it’s a good suggestion to remove the engine cover and search for any corrosion build-up near cylinder heads and thermostat housings that would indicate leaky gaskets. Also, look for corrosion at wire terminal connections… clean and tighten them as required after which use one of many proprietary anti-corrosion sprays available at your dealership on all exposed electrical connections and unpainted metal parts of your outboard.
Be sure that throttle and gear-shift controls operate smoothly. Lubricate them as needed. Bear in mind that it’s best to never shift gears unless your engine is running, so make sure that the boat is securely made fast to the dock before checking shift controls for smooth operation.

Next, run the engine with the cover off and check that not one of the bolt-on components (fuel pumps, voltage regulators, coils, and the like) have come loose from their mounts. Be sure all wires and cables are securely led and clipped through harness mounts. Next, if your engine is equipped with an engine mounted fuel strainer, check to see if any water has collected in it. Will probably be easy to see, because the water will separate from the fuel, drop to the bottom of the strainer, and be relatively clear in color in comparison with the fuel/oil mix above it. If you possibly can see water, remove the strainer housing and drain out the water. Clean the screen element, reinstall, ensuring the O-ring is in place before threading the housing back in, and re-check this assembly for fuel leaks after replacing the strainer housing. Simply pump your fuel primer bulb until the filter/strainer fills with fuel, and search for leaking fuel.

Check for corrosion at thermostat housing at top of cylinder head or engine block

Check for corrosion at all wiring connections

Next, you should check the condition of any sacrificial zinc anodes attached to your engine. Check for zincs at the lower portion of the mounting bracket on larger engines. There may be a zinc trim tab behind the propeller, or a small zinc screwed onto the antiventilation plate. Replace any zincs that are greater than half eroded. In some areas they’ll dissolve quite rapidly, and if the zincs are completely gone, the one thing left to dissolve is your engine housing.
Lastly, check your engine’s battery, and top up the cells as needed.

Seasonal Checks and Outboard Maintenance

First let’s define the word “seasonal.” The best way I apply it here, it actually means every three months, or every full boating season, whichever comes first. In other words, if you possibly can boat all of the year round, or for greater than three months anyway, do these checks and maintenance procedures at the very least once every three months, or about every 50 to 75 hours of operation.

But when you reside in a region where your boat use is restricted to lower than three months, or 75 hours, consider these “seasonal” checks to be annual checks.

Three-Month (or Seasonal) Service Checks

Seasonal check-ups are way more comprehensive, and certain operations may require the expertise of your local dealer, but you will certainly be capable of do all of the work listed here except in a number of cases.

Grease Points… All grease points on your engine ought to be full of fresh grease as recommended by your manufacturer for the specific engine location. Keep pumping in grease until all of the old grease-and any water-is forced out. It’s a messy business, so wipe the old stuff away with a rag as it emerges across the lube point.

Propeller Inspection… First, make sure your ignition system is disabled by disconnecting the spark plug wires at the plugs. Then remove the propeller to inspect the shaft for any fishing line wrapped around it. If you find any, cut it all off.

Inspect the propeller for nicks, burrs, and any unwanted bends within the propeller blades. If the nicks are minor, you possibly can clean them up with a file.

Inspect the propeller hub for any deterioration of the vulcanized rubber and its attachment to the hub spline. Any damage found here could spell trouble next season. If this hub is damaged, you may need either to have the prop rehubbed or a brand new prop. If you’re in doubt, have your dealer make the final call. You certainly do not wish to replace it if you do not need to.

If all looks okay here, wipe down the propeller shaft to remove the old grease, and apply a thin coat of an approved waterproof grease to the shaft. Do not reinstall the propeller just yet, as you are going to run the engine to flush the cooling system, and you must never run an engine out of the water with the propeller on because of the apparent danger from the whirring blades.

While you do reinstall the propeller however, remember to replace the cotter pin for the prop nut in case your engine is equipped with one. In case your engine uses a Nylock self-locking prop nut, it must be replaced, as these lock effectively only once.

Gearcase-Oil Change… The subsequent step within the seasonal service process is to alter the gearcase oil. On most outboards, the gearcase can have two screw plugs evident within the side of the gear housing. Some engines, however, may have the gear unit’s drain and fill screws located on the hub just forward of the propeller, wherein case they can only be reached with the propeller removed.

To drain the fluid out of your unit, wipe the skeg clean on the very bottom of the engine and attach a bit of masking tape to the skeg.

Get a clean container that’s large enough to carry all the oil in your gearcase and place it under the tape. Remove the lower drain plug. Nothing much will come out until you slowly unscrew the upper check plug. The oil will then leak down the side of the gear housing, down the side of the skeg, and flow straight down the edge of the tape into your drain pan.

Carefully inspect the oil for excessive metal filings or discoloration. If the oil appears milky, or if you happen to noticed a considerable amount of water coming out of the drain before the oil, then water has somehow migrated into the gearcase, indicating a nasty seal.

Clean off the magnetic pickup found on many lower drain plugs and get able to refill the lower unit with the correct gear oil.

A note of caution here: Don’t let anyone talk you into using straight gear oil as supplied by auto parts stores. Although this oil may have the identical distinctive rotten egg odour because the fluid you’ve got just removed from your outboard engine, it may not be the same stuff. Typically, the special outboard engine gear oils have a water-dispersant additive in them that’s not found in the automotive grades. Also, bear in mind that not all outboards use gear oil of their gearcases. Some use four-stroke engine oil, and others use a fluid quite much like automotive automatic transmission oil. Make sure to check the specifications on your engine. It is best to go to your dealer to buy a container of the proper oil and one of the special fill pumps.

These pumps are quite inexpensive and fit not only the oil container, but screw directly into the threaded lower unit drainplug hole in your engine, minimizing mess. This is an important point, because you’re going to fill the gearcase from the bottom up. Once you might be set-up , simply work the pump until you just begin to see oil seeping from the highest check-plug hole. Then reinstall the check plug and snug up the screw.

Next, get the drain/fill plug ready to put in, wipe down the magnetic pickup, and ensure the sealing Oring or gasket is either in place on the screw plug or in the gear housing. Unscrew the pump tool and quickly insert the drain/fill plug. Tighten it fully. Wipe off any excess oil from the gearcase and watch for leaks. Your oil change is complete.

Cooling System… The next step in the seasonal service is to thoroughly flush your cooling system with fresh water. A precaution here is to make certain that the flush adapter stays in place while you are flushing the engine. If the adapter slides down on the lower unit to a point below the water inlet, you may burn out the engine’s water pump-or the engine itself-if it’s left unattended for even a quick time.

As part of this cooling system service, it’s also a good idea to remove and clean your engine’s thermostat, if it has one. The interior cavity into which the thermostat and bypass valve fits is a trap for sand, salt, and general debris that gets past the system pickup strainer. With the thermostat removed, clean out any muck you discover there and, with the engine running, run fresh water up from the flushing adapter through the engine to this point. You’ll now know for certain that the inner water flow is unrestricted, because water will leak out at this point. Just run the engine long enough to determine that a very good solid flow of water is pouring out.

After the thermostat has been cleaned, reinstall it, using new gaskets, and run the engine again to make sure the thermostat cover is just not leaking. If your engine has gave the impression to be running too hot lately, but your inspection has now revealed that water is getting up to now in adequate amounts, the operation of the thermostat might be the problem.

Impeller Replacement. In addition to flushing the cooling system and checking the thermostat, you might also regard the replacement of your water-pump impeller as routine maintenance. To inform the truth, manufacturer’s recommendations vary on this score, some suggesting that you renew the impeller every year, and others that you just replace it only as needed. Should you regularly venture far offshore, where failure of the water pump could be a serious problem, replace that impeller yearly.

However, if you use your motor only occasionally throughout the season, or on a tender, for non-risky trips from ship to shore, I would advise you to replace the impeller every other year.
Cylinder Compression… Now that you’ve got run your engine for a bit to flush your cooling system, and have warmed it up, it is a good suggestion to perform the annual compression test. Remember, compression is one in all your engine’s basic needs and a compression check can often catch impending problems before they become major.

For example, piston rings which are just beginning to gum up will cause low compression before they fail completely. Usually, you possibly can cure this problem by running a manufacturer-approved decarbonizing fluid corresponding to OMC or Mercury “Engine Tuner” through the engine. If you don’t catch this problem in time, the only solution is to take the engine apart. It’s simple to make use of these engine tuners-the instructions are right there on the product label.

What’s often not really easy is finding out what normal compression is in your engine. Often the specs usually are not given within the engine owner’s manual or even in the workshop service manual. So it’s a good idea to check the compression when the engine is fairly new and in good running order. Write down the compression figures for each cylinder in your manual for future reference.

As a matter of interest, the actual pressure shouldn’t be that important-it is the variation from the norm that you should be concerned with. In the case of a multicylinder engine, start worrying if any one cylinder varies from the others by 15 pounds per square inch (psi) or more. If yours is a single-cylinder engine, a drop of 15 psi from the norm you established when it was new is cause for concern. The steps for performing a compression test are really quite simple, but you need to follow them exactly for your personal safety and the accuracy of the readings. So be warned-don’t skip any of these steps:

  1. First, disable the ignition system by unplugging the gang plug going into your ignition module. In case your engine has an emergency shutoff switch, simply remove the lanyard clip to disable the ignition. If neither of those solutions works on your engine, take a wire jumper lead and connect one end to a very good engine ground, and the other end to the metal connector inside the spark plug boot. You will have to make use of one jumper for each plug wire. Remember, simply disconnecting all the plug wires may be a dangerous move. When you remove all your spark plugs and start cranking over your engine, an explosive fuel/oil mix might be spraying out of the plug holes. A plug wire could spark and ignite this mix outside of the combustion chamber if it isn’t grounded to the engine. Also, this freewheeling type of spark could damage the ignition coils or modules.
  2. Remove all of the spark plugs, and be sure to maintain them so as so you may return them to the cylinders they came from. Carefully inspect the business end of the plugs, searching for any inconsistency in coloration, and for any sign of water or rust near the tip.
  3. Next, thread your compression gauge into the #1 spark-plug hole and “zero” the gauge.
  4. Open the throttle as far as possible, to make sure that the cylinder gets an unrestricted supply of air. (Some engines allow only minimal opening if the gearshift is in neutral, to guard against over-revving.)
  5. Crank over the engine an equal number of times for each cylinder you test, and you’ll want to re-zero the gauge for each cylinder. When you have

an electric start, count the seconds: “One thousand one, one thousand two, one thousand three, one thousand four” and so forth, with the important thing or start button engaged. This provides you with enough cranking time for a usable reading. In case you have a pull start, pull the cord four to five times for each cylinder you’re testing.
6. Record your readings from each cylinder for future reference. Use the 15 psi criterion already mentioned to find out if further action is required.

If compression readings are lower than normal for any cylinders, try a “wet” compression test, which can temporarily seal the piston rings, and determine if they’re the reason for the low reading.

To perform this test, get a can of your favorite fogging oil and insert the red nozzle tube in the push button. Now carefully insert the other end of the tube into the spark plug hole and spray into the cylinder with a circular motion to distribute oil spray all across the perimeter of the piston. Spray for about four seconds.

Remove the nozzle and install your compression tester. Spin the engine over exactly the same number of times you did for the previous test and compare your gauge readings. If the compression rises noticeably, then your rings are beginning to stick.

If you have caught the issue early enough, decarbonizing with an “engine tuner” fluid, as described above, may cure it. If the dry compression was really low, and no change is obvious through the wet test, it is too late. Your rings and/or piston are worn to the point where major engine disassembly might be required. So be brave, and consult your dealer.

If two adjacent cylinders on a multicylinder engine give a similarly low reading, or if there was evidence of water or rust on the spark plugs from these cylinders, then the problem is a faulty head gasket. That is usually an issue better left for knowledgeable to deal with, but you probably have enough engine experience, you could wish to tackle it yourself.

Incidentally, beware of compression readings from an engine that has been in storage for an extended period. While it is sitting idle, the piston rings will “relax” and retract slightly, often giving an initially low and misleading reading. Always run an engine to operating temperature to make sure that the reading you get is accurate.

One last tip-if the spark plugs have been within the engine for your entire season, now’s the time to replace them.

Fuel System… The following phase of the annual inspection is to thoroughly check your boat’s entire fuel system for any signs of leaks, loose clamps, or cracked, frayed hoses and squeeze bulbs. Any rust patches in your fuel tanks should be sanded and touched up. Also, inspect the venting system on your fuel tank. It must be free to breathe. Any restriction can stop your engine.

A simple strategy to check for a fuel leak from the primer bulb to the engine is to squeeze the bulb until it gets firm, and hold pressure on it to make certain it remains firm while the engine’s not running. If it does not stay firm, there is a leak within the system between the bulb and the engine, or within the engine itself at the carburetor or fuel pump.

You might have to remove some access panels in your boat to do a visual check of the entire fuel delivery system, but don’t neglect this important task.

Automatic Oiler… Your next job is to check the automatic oil-blending system, in case your engine is so equipped. Clean and inspect all lines and connections, replacing any cracked lines and tightening loose connections as required. It’s a good suggestion to check with your dealer for specific recommendations in your engine. On some engines, oil’ delivery pump diaphragms should be replaced as part of an annual service.

Steering… Your boat’s steering system needs to be thoroughly inspected a minimum of once a year, but don’t hesitate to see what’s amiss any time you feel unusual looseness or tightness within the steering wheel. Inspect steering cables for any signs of separation, cracks within the outer sheathing, or rust buildup near the cable ends.

Battery… Next, check and clean all battery-cable connections and battery tops. Smear a light coating of Vaseline or similar light grease over the tightened connection. If you’re planning to place the boat in storage, remove the battery and trickle-charge it every month.

Two Final Adjustments. Last, you should have your dealer set your ignition timing, and adjust your carburetor(s). These usually are not procedures the part-time mechanic should attempt on an outboard engine. There are simply too many expensive tools required.

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