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150 4 stroke Lower unit knocking at idle. Knock goes away at 7000 rpm. Mechanic says; "Yamahas do that or may be clutch dog"!, I have a feeling he may be inducing sodium deposits in me if ya know what I mean... What say You?
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That motor should not be turning 7000 RPMOriginally posted by SUPERSPOOKY View Post
Some motors have to have the drive shaft preloaded with spring washers, if they are not installed properly they make noise.
Heavy SS props can cause this noise in gear at idleLast edited by 99yam40; 01-24-2015, 10:47 AM. -
two things come to mind.
some stainless props simply chatter and while its annoying its totally harmless.
the other is someone has improperly installed the lock ring and collar on the water pump impeller.
there again annoying but wont hurt anything.Comment
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I say this is a very common and well understood phenomenon in four stroke motors. So much so that both Yamaha and Mercury Marine have designed new style propellers that mitigate the issue.
It is referred to as prop rattle or prop chatter. No harm is being done. It is merely a nuisance.
I suspect that you have a stainless steel propeller. Switching to an aluminum propeller or the new style of stainless propeller will help to reduce the noise. The clunking that you hear when the motor is shifted into gear will also be lowered.
http://yamahaoutboards.com/sites/def..._5-FINAL_1.pdfLast edited by boscoe99; 01-24-2015, 10:56 AM.Comment
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the best performing prop I tried on my F150 was a custom 13.5x18.
however the prop chatter idling down the canal was to annoying.
so I settled for a Yamaha SS in 13.25x19.
so other than an engine miss issue or a case failing there are two reasons for that knock.Comment
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