many years ago when i rebuilt my first out boards ( long before the internet and without a service manuals) i would just plonk the impeller in where it went IE: push down whilst turning the shaft , never had one fail from my inexperience not knowing the correct direction.
later i learned that on the first start up they instantly flip to the correct direction by themselves after i intentionally put one in the wrong direction and took it apart shortly after to see the result , sure enough it flipped.
so in saying that , yea , it could cause issues 100 hours down the track if the impeller was not soaped up ,IE: put in dry. but even then it would still eventually with normal water lube change to the direction it needs too within a short time after start up.
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