On Sunday 01 August 2004 6:18 pm in rec.boats mijoy wrote:

I have twin 100hp 4-stroke Yamahas. They have about 900 hours on them.
So
far this season I have developed major problems with both. I'm begininng
to
question the longevity of the 4-stroke yamaha. I'd guess that there are
not
too many of these engines with 900 hours on them. I'd be willing to wager
that these engines are flawed. I think it is the same block as the 90hp
so the problems might also be on these motors.

Manufacturers work on the average utilisation of a leisure boat being 100
hours per year. Outboards are designed to deliver maximum power at minimum
weight, which is not the best formula for longevity.

If you want maximum life under heavy uasage you should be using inboard
diesels rated for continuous duty. Take a look at the CAT website where
they rate their engines according to the expected duty cycle.
Typically an engine rated at 600 HP leisure use is derated to around 350 HP
continuous duty.


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