The Yamaha 5C outboard motor is one smooth little engine.

Crossflow outboard motors like the Yamaha 5C have a ridge atop the piston crown that makes the air/fuel mix swirl from the cylinder wall intake port on one side to the exhaust on the other.

Back in the ‘70s crossflow two-stroke outboards were all the rage. Mercury and Outboard Marine (Evinrude and Johnson) loved them, but not the Japanese manufacturers. That was up until late 1982, when Yamaha released its crossflow 4A and 5C outboard motors, which were also the first outboards in this power range to run on a 100:1 fuel/oil mix.

Crossflow outboard engines have a ridge atop the piston crown that makes the air/fuel mix swirl from the cylinder wall intake port on one side to the exhaust on the other. The air/fuel mix is burnt more thoroughly than in a loop-charged engine and, combined with the larger flywheel needed to smooth-out the greater piston weight, crossflow engines always vibrate less when trolling than loop-charged units.

The trouble is, the larger flywheel means more fuel is needed to power the engine than comparable loop-charged engines so exhaust emissions are much higher. Yamaha’s 5C has an OEDA "0 Star" rating compared to Mercury’s loop-charged 5 which is rated "1 Star".

Not long after I acquired a 1967-model 6.7m plywood Bluebird cruising yacht I contacted Yamaha Motor Australia about borrowing a longshaft Yamaha 5C to see how it would compare with a series of 8hp engines I’d been testing on the hull. The brand new engine arrived complete with a tiny five-inch pitch weedless prop to let the engine rev well out, which is the secret to good performance and engine longevity with any outboard auxiliary.



The Yamaha 5C outboard motor has a 103cc powerhead that develops five brake horsepower (bhp) at 5000rpm with a Wide Open Throttle range of 4500 to 5500rpm. The cylinder head and block are integral with an unboltable hatch in the head to clean the cooling water passages. There’s CD ignition with electronic timing advance to reduce maintenance. The 5C can also pivot 360-degrees in addition to having forward, neutral and reverse. The effective thermostat maintains even engine temperatures year round.

Five trim and three shallow water drive positions are fitted so the 5C would also suit smaller trailersailers. A 5amp 12V alternator can be fitted for powering nav lights and basic electronics.

The metal 2.8lt integral fuel tank provides an adequate range and the rubber seal on the cap seals tightly against vapour loss, which can be a problem with plastic fuel tanks on hot days.

A large carryhandle and three fingergrips make lifting the 5C inboard from a transom bracket very easy – even weaklings like me can lug this 21.5kg engine around.

Servicing the 5C is straightforward, although as the spark plug electrode gap is only 0.55mm the plug tends to foul very quickly at low rpm.

There is also a problem with the gearshift lever seal deteriorating rapidly due to hot exhaust gases passing it, necessitating removal of the powerhead from the pan to replace the seal in the loan 5C after 60 hours of running.

Yamaha recommends servicing the 5C every 100 hours or annually after the first 20 hours and for the life of the loan unit I used standard unleaded petrol (91) with Yamalube 2M oil.

After 100 hours of saltwater leg/lower unit immersion, no corrosion was apparent anywhere on the loan engine.



The tiny prop worked well with the 2.08:1 gear ratio but, being weedless, power astern was miserable. I came to think of the Yamaha 5C as really only having a clutch for neutral warm up, as slackening the steering friction and swinging the engine 180-degrees for more power when reversing was a pain.

After carefully running in the engine it was subjected to the usual hard outboard auxiliary life, such as not being freshwater flushed after every run. But it usually started first pull and across the entire rpm range vibration levels were very low for a single.

There was no fear of separating the transom sheeting from its framing, as did two other loop-charged singles on this hull. And with its reasonably quiet running, the engine definitely wasn’t the start of my tinnitus.

Pushing a total of 1800kg the 5C ran out to slightly above a hull speed of 5.9kts but throttled back to three-quarters could maintain this all day. Dropping back to two-thirds returned very good fuel efficiency without losing much speed – the joy of all pure displacement hulls­ – and at this throttle opening would still maintain 4kts into stiff headwinds.



The Yamaha 5C is showing its age now, especially with the running qualities and fuel-efficiency of its four-stroke 5-horse counterpart.

But used as a kicker between pockets of wind, the light weight and low vibration of the 5C are hard to beat. I tried a four-stroke 5 on the Bluey and the old transom fasteners let me know pretty damn quick this wasn’t the way to go!

As of April 2014 the longshaft 5C retailed for around $A1900 with a spare prop for $A120.

Thanks go to Yamaha Motor Australia, Murarrie, QLD, for saving my Bluey’s transom!  Phone them on (07) 3906 7000.



Yamaha 5CL. Average of two-way runs across a measured distance, calm water




4000 (2/3 throttle)



4900 (3/4 throttle)



5200 (WOT)



* Sea-trial data supplied by the author.



TYPE Single-cylinder petrol two-stroke outboard


REC. RPM RANGE 4500 to 5500


BORE X STROKE 54 x 45mm



RRP $1900

WARRANTY 3 years


Originally published in Trade-A-Boat #243, July / August 2014. Why not subscribe today?

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