Outboard Motors

on the
Outboard Motors
used by the
Murray River Expedition

15-23 March 1981

SIX 3.3 metre flat bottomed aluminium dinghies were powered by 1974 7.5 h.p. Blueband outboards. Five motors covered the entire distance. Three others were interchanged on the sixth boat.

Prior to the expedition all motors were completely overhauled (rings, bearings, oil seals, ‘O’ rings). From this time till the end of the expedition the motors were used for approximately 80 hours – including practice and racing. Of this time 79 hours would have been at maximum speed. It is suggested that this is the equivalent of two years use by the ‘average’ owner.

River conditions varied but were mostly favourable. Headwinds sufficient to cause uncomfortable chop were encountered for approximately 15% of the journey. Total all up weight (boat, motor, crew, equipment) averaged about 200 kg.

Quicksilver Formula 50-D two stroke oil was used for the major part of the journey, till supplies were exhausted. Golden Fleece Superkool two stroke oil and other two stroke oils were then used.

Refuelling was effected by interchanging of tanks with the Support Crew who were responsible for obtaining and mixing the fuel and oil. This was an area of concern but even with more than 30 fuel stops (mostly made under adverse conditions and with very little time) no mistakes occurred with fuel:oil ratios. Fuel consumption averaged 4 litres per hour.

Quicksilver Lower Unit Lubricant was used in the gearboxes of all the motors.

All drivers were experienced in power dinghy racing.

There were no qualified mechanics among the expedition members, however six members could be classed as ‘bush mechanics’ and were sufficiently experienced to strip and rebuild 7.5 h.p. Mercury outboard motors from top to bottom (and have no parts left over).

Spare parts were carried by the Support Crew – their projected usage being dictated by racing experience in such events as the Avon Descent and Blackwood Classic 250. Parts other than those carried were also used and not all parts carried were used.

When all factors are considered, including that, for all motors, the total distance travelled was 13,500 kilometres and the total usage of the motors was 500 hours, relatively few problems were encountered.


1 x Propeller shaft oil seal damaged
1 x Pinion gear stripped
4 x Rubber mounts broken, popped out
1 x Male fuel bayonet snapped off
1 x Timing bolt vibrated off
8 x Nuts, powerhead vibrated off
1 x Gasket, powerhead to cowl blew out
1 x Gasket, carburettor blew out
4 x Bolts, start recoil assy vibrated out
2 x Screws, switch box vibrated out
2 x Forward gears stripped
1 x Flywheel key broken
1 x Ballbearing, 6005 damaged
1 x ‘O’ Ring, bearing carrier damaged
1 x set of reed valves broken ends
4 x Propeller shafts bent, worn
4 x Crankshafts Worn
2 x Drive shafts bent
8 x Con rods worn
2 x Drive shaft housings cracked, broken
1 x Throttle butterfly rod worn through

*   Damage and/or wear did not become evident till motors were stripped at the conclusion of the expedition with the exception that some propeller shafts were re-straightened enroute.


Retaining ring worked loose causing loss of gears
Inlet port covers worked loose
Split fuel line
Propellers bent and damaged
Propeller shafts bent
Water in gearboxes each day
Start recoil sticking continuously – one motor only
Spark plug boot worked loose – one motor only
Powerhead nuts worked loose each day
Miscellaneous nuts and bolts worked loose
Covers vibrated looseNeedle and seat sticking continuously – one motor only
Rubber ‘O’ ring under fuel tank breather screw caused fuel leakage – all new tanks
Various unknown carburettor and electrical problems
Frayed wires – unknown cause


Powerhead bolts need tightening regularly and are inaccessible. There is no tool suitable for this task, particularly the rear nuts.

Supply of urgently needed parts was not good and caused problems.

Leaking fuel tanks are a safety problem and appear to be a quality control problem which can be rectified quite simply.

CHAMPION spark plugs are preferred as they do not carbon up as readily as do AC spark plugs.

QUICKSILVER oil showed a marked performance increase over other brands of oil that were used.

Generally, motors started first time, every time.

Breakdowns and faults generally occurred after a stop (re-fuelling, locks, nature calls, etc). Many problems occurred as a result of a very minor problem becoming a major breakdown. For example, powerhead nuts vibrated off causing gasket to blow out thus necessitating the removal of the powerhead.

Vibration, though comparatively slight, is a comfort consideration in an extended use situation.

Fuel consumption varied only slightly between all motors and was constant throughout the expedition. Variations that did occur in fuel consumption were not of sufficient magnitude to effect route planning.

The motor cover holding catch is not positive enough and should be re-designed to be more secure. One cover was lost overboard because of this defect. The loss could have been prevented by tying the cover down but it was considered that this would not be good publicity. This is also a safety consideration, especially in the sea.

Two blade 9 x 9 propellers proved to be the best all round for the conditions encountered.


© Kim Epton 1981-2022
979 words, three photographs

Text and layout Kim Epton
Photographs by David Whitney, Tony Poole, Vic Watt, Roly Ritson

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