200 hp Yamaha issue

birch812

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Sep 1, 2010
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I have a problem with a 200 HP Yamaha outboard and need some advice.
While fishing last Saturday the engine suddenly revved up which I immediately shut down. We started it back up but noticed the engine was not circulating water and shut it back down, all well in advance of the over heat buzzer going off.

We limped back in on the starboard engine the 36 mile run to the dock and took the boat to the dealers the next day.
The dealer called and said that the driveshaft had spun in the crank and we would need to replace the power head, shaft and lower unit.
My question is how could this engine have such a catastrophic breakdown when we didn?t hit anything, there were no bangs, squeals or grinding noises prior to the engine spiking up to 6400 RPMs?

The dealer said he only saw this one time before.
Now I can understand how the shaft could spin with wear, and I can even understand how it could wipe the female splines out in the crank but why would I also need a whole lower unit?
There was no smashing of gears and until this happened, the engine has always run flawlessly.
The engines are well maintained; the power heads were both replaced 4 seasons ago and has less then 250 hrs, and in June both lower units were down to have the water pumps replaced and lower seals.

I don?t know how the dealer can tell the crank splines are wiped and why he could not put in another shaft. In the scheme of things I assume the crank would be harder then the shaft and considering the engine didn?t hit anything and didn?t stall or shake the shaft may have just had rust or electrolysis issues that could account for its weakened condition.

Any advice would be greatly appreciated, since the new power head and lower unit will run over 8K and replacing the engine would require buying 2 engines since I have counter rotating pair.

Thanks in advance for any advice.
Birch
 
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