Regular servicing of your tender outboard is a must

A trip on the Myall Lakes some years back did not quite become a disaster, but our holiday was certainly interrupted when water stopped spurting from the tell-tale on the outboard engine.

We were in a remote location and faced with sitting out some terrible weather with three bored teenagers for the rest of the week; even rowing the inflatable three miles back to the car was looking attractive.

With the crew preparing to recreate the incident on the Bounty, the appearance of a friendly yachtsman was more than usually welcome. He showed me just how easy it was to remove the weed that had clogged the water pump and get the recalcitrant engine running cool again.

My first job on returning home was to purchase some relevant books and find a friendly mechanic to get some lessons in basic engine maintenance.

How hard can it be

That was thirty years ago and the simple skills I gained have since served us well.

A small two-stroke outboard engine is a relatively simple machine and many of the problems we encounter are readily preventable if we attend to the essentials in good time. Of course we can take it along to the shop each year for servicing, but given its relatively low cost, it tends not to make economic sense.

Other than the gearbox they do not have oil to change and once you grease and oil the important bits there is not a lot left to do on a two-stroke. After all you still have the oars if it all goes wrong.

The best way to keep the engine running well is to use it properly; long periods of inactivity leave it a little stiff and lacking in the protective oil layers that allow free movement. Impellers will harden and stick, plus any residual oil can clog the carburettor when the petrol evaporates. Of course, regular flushing will keep the cooling water passages clear.

Even though my outboard is a 2.5hp Mercury, most of the small engines are either similar or in fact identical as many are simply rebadged. You need only a small selection of tools (usually a ring spanner – mine uses 10mm hexagonal heads on the bolts I need to take off), some waterproof grease, a screw driver, lubricant spray and gear oil.

Here is what I do occasionally

Before doing anything on the engine remove the plug lead, this prevents the engine starting accidentally.

Have a good look around for anything that appears odd. I look for corrosion and like to give some oil to anything that pivots. These are on the carburettor throttle control and choke and on the engine pivots.

If you bought an engine with forward and reverse gears, then grease or oil these pivot points.

Look at the anode; this is usually under the anti-ventilation plate just above the propeller. It should show some signs of pitting if it is doing its job, but if it is badly corroded then replace it.

If there is a lot of white powder on it, then lightly brush with a wire brush to restore it. Never paint it or cover it with grease, it is meant to corrode and save the engine.

You will of course have noticed that each time you run it there is plenty of water gushing from the tell-tale.

Here are the jobs I tackle each year

Change the gear oil. It should feel oily and be clean. If it has gone milky then you have water in the gearbox due to a failed oil seal.

Any grit means that the gears could have been damaged, this could now be a good time to visit the workshop. While this is not difficult to fix, it is beyond the scope of this article on general preventive maintenance. My engine uses SAE90 oil in the gear box.

Change the impeller in the water pump regularly as these harden with age. If you use the engine a lot, then change it every 100 hours. This job is not difficult so do not put it off. Even though they are costly (mine was $40 for the last one), they are cheaper than a cooked engine.

If there is a filter on the fuel line (I installed one after a problem with dirty fuel some years back) then inspect it. It should be clean, but change it if you have any doubts. Be sure you do not kink the fuel hose as this will reduce the fuel flow and cause the engine to stop when least convenient.

Check the spark plug, this should be clean with no black oily build up. The washer should also be clean and not damaged.

Check the spark gap; the correct gap will be listed in the maintenance book that came with the engine – mine is 1mm (0.040 inches).

While the plug is out, fully extend the starter cord. If this is abraded, then have it replaced as once it breaks it is nearly impossible to start the engine. It is also a difficult job that takes much patience and uncivil words.

Use this opportunity to inspect the propeller; it should be smooth without any nicks or chips in the blade edges. Any minor chips can be smoothed with a file, but be careful. remove too much material you will unbalance the prop and make it vibrate. Any major damage should have you heading off to the shop for a new one.

Finally start your outboard up after doing these tasks and listen to it. Check to see if water is gushing out the tell-tale.

Then adjust the throttle, the engine should accelerate smoothly to maximum revs then back to idle. It should idle smoothly; check the stop button as the wires can occasionally be dislodged while working on the engine.

Never be tempted to start the engine out of the water. I have seen some ‘cool dudes’ do this on the boat ramp; but leave it to them, – apparently they have more money than they need!

Petrol and aging.

Don’t use ethanol mix petrol as the alcohol can absorb water giving phase separation and it might affect gaskets. A more complete examination of fuel problems was published in CH July 2011.

Do not keep the petrol mix for too long. If is getting a bit old (maybe after six months if kept cool in a sealed can) then put it in the car – it will dilute in the tank, the oil in the mix is not harmful to the engine.

Get the oil fuel mixture ratios right for your engine. Generally there will be a higher amount of oil for the initial run-in period then a lower mix ratio thereafter.

If you have a four stroke engine then you will need to change the sump oil. Generally this is recommended each 100 hours or each year, whichever comes first.

Use the recommended oil. It is unlikely there is an oil filter, but check your hand book.

No matter how much you care for the engine it will accumulate some scratches and chips. I have yet to see an engine that does not corrode.

This can can be treated by wire brushing the bubbled paint and white aluminium deposit and spraying with an etch primer. I found that White Knight gloss spray enamel black is a perfect match for my Mercury outboard. Be careful painting plastic parts as the paint solvents can attack them.

By keeping the grease and oil up to the engine and keeping the cooling channels open you should have the engine working well for many years. Fixing up any chips and dings as they happen will keep it looking good for just as long.

And if you are familiar with how it all goes together then any minor problems can be ironed out – handy in a remote location; with the money left in your pocket put to better use.


– John Tylor: John is a retired electrical engineer who lives in the Blue Mountains west of Sydney, Australia. He and his wife Patsy cruise the east coast of Australia when they can, but he is currently upgrading their venerable Duncanson 35 yacht Ard Righ.

John has repaired the electrics on many yachts and gains his inspiration from these experiences as well as from the many upgrades to his own boat.


This article was first published in the January 2014 issue of Cruising Helmsman.


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