Noise is probably the biggest concern. Cost second. The boat motors often had better internal components because they:
a) Sold independently at a higher profit margin
b) Were often operated by slamming the throttles open all the way and crusing the boat for hours on end (especially salt water boats).

I must say, however, that I have steel gears in my PV's motor, and I can't say that I really hear any noise from them. But then again those DCOE's and the loud exhaust tend to cover up more subtle noises...

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I'm JohnMc, and I approved this message.