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Servicing small outboards

 

 

Introduction to these servicing pages

The question often arises :  “Can I service my own outboard”.  The answer is a qualified “Yes”. However, whilst I am happy to pass on the benefit of my long experience of outboard motor ownership, these notes are set out without charge and without responsibility. I am not a professional mechanic nor a qualified teacher of mechanics so you do DIY servicing and follow my notes at your own risk. If you are not prepared to proceed on that basis and want to be able to sue someone if you have a problem, then please follow your manual to the letter and take the motor to a professional for servicing. If you have an opinion different from mine about these subjects, an experience or information to share then please drop me an email by substituting “douglas@” for the “http://www." in the web site address.  

 

Here are links to the detail pages but I recommend that you read to the end of this page once before opening the detail pages for the first time. The links are repeated at the bottom of this page.

 

The service                      How I do my annual service

 

Maintenance record          A form that you can use as a check list and record of your annual maintenance

 

The water pump impellor  How I get inside the bottom end

 

If you have done a little car maintenance, then all the regular preventative maintenance items are relatively easy. The only tricky item is the water pump impellor which can be awkward to get at but in my opinion, as discussed below, does not need attention every year. As you see it is dealt with separately.

 

I have a 6HP Mercury which, despite a number of internal differences between the engines of different years and different power outputs, can be considered for this purpose to be the same engine as the single cylinder 4HP, 5HP and 6HP four stroke outboards branded in the UK as Mercury, Mariner or Tohatsu - and in the USA as Nissan. The most obvious difference is that the 4HP motors and the larger models of some brands have an integral fuel tank but this does not affect the servicing beyond the need to turn off the fuel and take care to avoid spillage. These light and economical motors are deservedly popular on Drascombes until around 2011 when the tiller handle grew so long as to foul the mizzen mast on Luggers, Longboats and Coasters. (most of the fleet)

 

Users of other motors of similar size may also find these pages useful. Although the list of items to be dealt with will differ, as will the oil capacities and plug gap, the basic layout of small outboard motors of different makes is very similar. The article is less applicable to two strokes and is probably least applicable to older two strokes with ignition contact breaker points to consider – but then if you have one of those you probably know how to service it.

 

For the service described in the link above you will need a set of metric spanners or sockets that includes a 10mm socket for the oil drain plug, a 17mm spanner or socket for the propeller and if  you have one, a 16mm (5/8”) plug socket for the spark plug although the box spanner and tommy bar that you should have in the engine tool kit may serve. A regular screwdriver, hammer and pliers will deal with the propeller split pin. The pliers should be regular size, not tiny electrical ones although ones with a longish nose are best. A large regular (for slotted, not cross head screws) screwdriver is also needed for the gear case oil plugs. Finally you will need a set of feeler gauges, a small wire brush, an oil can and a grease gun. If you tackle the water pump impellor you will also need a 13mm spanner. It may help your confidence to remember that ultimately, if you come across something you can’t handle you can still take the motor to a dealer.

 

Only routine service is dealt with here so if your engine is not running properly, and does not respond to a new spark plug, then beyond checking for overheating or a blocked fuel filter you probably either have tuning issues or obstructed carburettor jets and will need to do some dismantling, ideally with a workshop manual, or will need a visit to your dealer. It is possible to adjust the slow running mixture but due to emissions requirements there are physical obstructions to discourage this. In some models a blanking plug has to be removed to get at the screw and in others the screw has very odd shaped head. A tachometer is required for setting the slow running which is why tuning is outside the scope of these notes. The slow running became more reliable after the 2006 model year when variable ignition timing was introduced to further improve emissions but the idle speed on load remained at 1100 rpm.

 

What actually comprises a service?

Working out what tasks should actually be carried out in your annual service is the least straightforward part of the job. In my view the maintenance instructions in the “Operation and Maintenance” manual which came with my 2002 motor contained some suggestions which I regard as nonsense, like replacing the fuel pump diaphragm, and inspecting the water pump impeller annually. The reference to the fuel pump diaphragm thankfully no longer appears in later manuals but the annual water pump impeller inspection is still there. In fact the manual which came with my 2009 Mercury says to actually replace the impellor each year. I regard that as unnecessarily frequent for most owners – see “occasional items” below.

 

Firstly, you have to estimate your motor hours (I used to keep a log until I got an hour meter). In a car these days the maintenance schedule is often every 10,000 or 12,000 miles or every year which ever comes around first – sometimes even longer still. Cars however, have modern oil filters. Our small outboards have no oil filter at all. In the days before modern lubricants and effective oil filters the service interval for a car was more like 1,000 or 3,000 miles. The outboard service interval is based on 100 hours which, with the constant speed running of an outboard and modern lubricants I reckon is very roughly equivalent to about 3,000 car miles.

 

A few years back one owner asked : “I do on average 12 hours a year and have usually had it serviced every year. I missed last year and in the previous year it cost me £175.00.”

 

If I was only doing 12 hours per year and was going to do the work myself, I would still give the motor the annual service as below. It takes less time to do than to write about, uses very little oil and grease and it is a chance to check the motor over.

 

On the other hand if I had to pay a dealer to do it I would not lose any sleep about skipping one year although I would still flush the waterways whilst checking the cooling water tell tale (which you should do every trip anyway), look the engine over, check the engine oil level, wax the paintwork and use the old petrol in something else. If the motor lives on a mooring all summer then I would also do the little oil and grease chores on the pivots etc., grease the prop splines, wipe the leg down, WD 40 the power head and wax the paintwork. In fact I would do these mid season as well if the opportunity arose.

 

By the way, remember that combustion creates acids, moisture and particulates which do no good at all sat in the sump of the motor all winter. In 12 hours running you are not going to create much of this muck but I wouldn’t skip more than one year and when you do service the motor, it is better done in the autumn than left to the spring.

 

I do between 25 and 55 hours per year – very seldom flat out and in the last 6 years have averaged 45 Hours. If you keep your boat in the water you may do more hours than me and need to consider varying the schedule. If you think you do more than 100 hours a year then you need to do the whole service every 100 hours – certainly the oil change -  and could even think about getting a Tiny-Tach combined hour meter/rev counter to keep an accurate track of the engine hours. (Follow the Drascombe Projects link to Engine Mods to see a mounting for such a device)

 

Click on the link to view the details of the service:

 

The service  . . . . . . . . . . . How I do my annual service

 

Maintenance record  . . . . . A form that you can use as a check list and record of your annual maintenance

 

The water pump impellor  . How I get inside the bottom end

 

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