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
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