Join Date: Dec 2008
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For what it's worth, here's what I think:
The only advantages of 4 stroke engines are fuel economy and silent and cleaner running.
Next come the disadvantages:
They are a lot heavier (at least 50%) for a given power rating . This can be a problem in boats with a non centered engine mount bracket.
Their cost almost doubles that of a similar two stroke
They require more expensive and extensive maintenance more oftenly: Timing belts, valve adjustments, oil changes, the works... A two stoke only requires a spark plug every once in a while, gear oil every 100 hours and little else.
They are mathematically much more prone to failure, courtesy of the array of moving parts they need to run and that are, each and every one, subject to failure. A two stroke has essentially two moving parts: A crank, a piston and a connecting rod. No valves, no camshaft, no oil pump, no springs, no rockers, no timing belts, no tensioners...
This said, and presuming that no one intends to motor-sail across the Atlantic with an outboard, I find it very difficult to understand why to use a 4 stroke just to save a couple os bucks in petrol, since that seem to be the only game where they innequivocally win...
My trimaran has a Tohatsu 5hp, two stroke single cylinder outboard which lives all year round in sun and rain hanging on his bracket and has never missed a beat. He burns quite a bit of petrol if compared with a similar sized 4stroke (2,5L/h at full throtlle), thus being comparatively a bit more expensive per mile, but it is much lighter, simpler to operate and run and cheaper to maintain and has a much better weight to power ratio. In four years it has only cost me a spark plug, 1/2L of 80W90 gear oil and an anode... I guess that for the miles I intend to be motoring the extra expense on fuel doesn't bother me at all...
Furthermore on this subject, even the fishermen are returning to two strokes arround here. They got tired of changing oil and timing belts in their fancy Hondas and Yamahas and have returned to the good old carburettor two stroke Tohatsus and I don't ear them complaining.
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