How to Work on Your Own Outboard Motor

Contrary to popular opinion, it's easy for do-it-yourselfers to do the basic outboard motor repairs, including changing engine oil and filter, gear case oil and sparkplugs.

Sometimes if you ask for a parts discount, based on the fact you are a do-it-yourself, you get it. Sometimes you don't. Don't make the mistake of skimping on oil quality. Four-stroke sumps hold a minimal volume of oil. Engine loads are high. Contrary to a car engines life cycle, outboards never coast down a hill. Combustion heat is like a mini refinery, boiling off lighter oil molecular and sapping additives of their strength. Combustion by-products dirty the oil. The older the oil, which is to say the more engine hours logged, the less efficient it is.

Oscar Zerk invented the zerk fitting
for grease guns.

Oil change completed, grease the zerk fittings, but only after having first wiped them clean. Otherwise, the grease gun will force dirt and grit into the very surfaces you're trying to protect. Consult the owner's manual to locate each and every one of the fittings. Pump in new grease until old grease oozes out. The old grease may well have still been viable. But pumping in new grease expels moisture that might otherwise cause corrosion. One last step with the grease gun, remove the propeller and grease the prop shaft spline. Should you notice any monofilament fish line wrapped around the propeller shaft, cut it off. Then pay special attention to whatever liquid drains out of the gear case. More on that later on in the story.

For the same reasons as crankcase oil, a new engine's gear oil is meant to be changed after the first 20 hours of operation. But don't rush in. First, get your hands on a long shank screwdriver. The extra leverage makes it easier to wrestle out a stubborn screw plug.

Crack the lower drain plug just enough so that whatever liquid is inside trickles out. Take note of what you see, then remove the top plugs and then remove the bottom plug entirely, draining the contents into a catch pan. Water, even a couple of drops, is a bad omen. So too is a chocolate color. Water intrusion happens when fish line wraps around the propeller shaft then burrows inward, cutting the shaft seal. Whirling gears pressurize the oil, forcing it out through the damaged seal. When the engine shuts down, the missing oil leaves a vacuum. The vacuum sucks in water. Unfortunately as little as an ounce of water can destroy a gear set. The only remedy is to replace the seals, usually a job for a pro.

If instead of water, you catch a whiff of burned oil, that too portends evil. Take a finger full of oil and sniff. Rub the oil between your fingers noting whether it feels gritty. Look in oil drain pan for broken bits of steel or bronze. Some techs poke a magnet into the drained oil to see if it will pick up small bits of ferrous gear metal.

To refill the gear case, Snip the top off a tube of lubricant and squeeze the oil into the bottom plug. Replacing top drain plug will hold the new oil in the reservoir long enough for you to get a fresh tube in place. For a few dollars can also invest in a dedicated pump. Before replacing the screw plugs, fit them with new gaskets to insure a tight seal. Then account for the old ones, one per screw. Examine the housing recess where the screws fit, making sure a no gasket is not hiding there. Two gaskets just don't work. In fact, they will cause a leak instead of sealing.

Now remove the engine cowling. Replace the on-the-engine fuel filter about every 100 hours. Common wire ties work great for hose clamps. Go wide, not narrow, for optimal goodness of fit.

What about a sparkplug change? Gapless sparkplugs are plug-and-play easy. Right out of the box they're ready for installation. Just be careful not to over tighten them, otherwise you risk the complication of stripped threads. Classic side gap sparkplugs are often preset. But be sure to double check the electrode to side gap clearance with a gaping tool. Owner's manuals specify a range, say from 35 to 40 thousandths of an inch (. 034 - . 040).

Savvy marine engine technicians adjust spark plug gap closer to the smaller number for the simple reason as an engine logs hours its sparkplug gap widens (Roughly . 001 every 20 hours). A tighter initial gap means the engine stays in tune longer. For example, assuming 100 hours per season, an engine tuned with . 040 plugs would be ready for a tune-up by the end of the summer, while an . 035 engine would be good for another year.

Battery posts, terminals and cables must be bright and shiny clean. Otherwise, green, gritty, corrosion bottlenecks outbound current flow to the starter motor and electronics plus resisting inbound charging from the engine alternator. A dedicated post and terminal tool with its male and female wire brushes gets the job done quicker than the time it takes to explain it. Clean the battery top with a solution of baking soda and water, being careful not to let any get into the cells.

During the season regularly dose fuel with stabilizer to prevent it from turning sour. That's because after just a few weeks gasoline begins to destabilize, transforming itself into gum that can clog carburetors. Smelly murky gasoline is a bad sign. When dosing with stabilizer, more ounces per gallon of gasoline equals more months of protection. Also consider periodically dosing gasoline with fuel drier. Ignore the cheap brands on the shelf that sell for a buck or two. They are nothing more than alcohol. The better ones sold by engine companies and MD actually absorb water and flash it off in the combustion chamber.

Fuel injected engines benefit from an additional canned cure. Wax build-up on the injector nozzles cause fuel to dribble instead of mist. The fix, dose the fuel with injector cleaner, or a tankful of high octane gas. You're not buying octane, you're buying a superior additive package that unplugs fuel injectors and scrubs carbon from the combustion chamber. With either method, the before and after difference is dramatic.

Finally, no matter which canned cure is prescribed, it's vital to read the label on the can and strictly follow directions. Protect fingers and eyes with gloves and goggles.

© Copyright by Tim Banse.