Knocking issue

[Fountaine]

I am new to Yamaha ownership and have a 95 150hp. So far love it.....

When the engine is running and I shift into gear I get a knocking sound that goes away when the RPMs increase.

This happens every time I have low RPSs and in gear.

A mechanic said one of the cylinders has a wobble in the wrist pin. He did not think it to be a big issue.

We shifted into gear with the engine shut off and there did not seam to be any play when we rocked the prop.

Does anyone have any thought on this. Thanks in advance.

[rodbolt17]

my thought would be the water pump wave washer and flat washers got installed incorrectly or left out.\
could be simple prop chatter but that did not have much of that issue.

[Fountaine]

Talking further with my mechanic, he indicated with the early 9-'s engines it was not uncommon for the there to be a knocking in the lower unit. He said it was an issue with the shaft knuckles when engaged and a low idle load.

It certainly isn't something that bothers him.

He has never lead us astray and I have trust in his knowledge.

If anyone out there has contrary info I would like to hear it.

[99yam40]

Rod is a Yamaha Master tech so I would tend to take advice from him .
Is the mechanic you are dealing with some one that has knowledge or trained on Yamahas?

[rodbolt17]

Iam calling out the idiot card.
use a tad of simple logic.

a wristpin and its bearing are mechanical parts.
once worn enough to knock it knocks all the time ,but usually not for long.

there are no shaft knuckles in any Yamaha outboard products.

certain 3.1L engines in the late 90's did have some prop chatter issues at idle speeds.

yours is a 2.6L.

in 1995 Yamaha deleted the spring assy that kept the lash out of the pinion thrust bearing and went to the washer assy on the impeller.
assemble it incorrectly and you get a knock at idle speed in gear.

much above idle speed and the normal push off from a spiral bevel cut geat holds it up.

I cant tell you how many I have seen installed incorrectly or simply left out.

[robert graham]

Is a shaft knuckle some kind of universal/CV joint?...

[boscoe99]

Shaft knuckles may be someone's term for the clutch dog teeth bouncing off of the gear set teeth.

Do a search for four stroke prop rattle or prop chatter. It is quite common in four strokes. They don't have as many combustion cycles per revolution which makes it a bit more prevalent. Moreover, they are so quiet the noise can be very noticeable.

Text book situation is the noise is heard when the low unit is in gear and the motor is at an idle, or maybe just above idle. The noise will go away as the RPM is increased since the gear teeth become locked together and don't bounce off of each other.

No damage is occurring. It is just a nuisance noise.

Oh, it is much more noticeable if a large stainless steel propeller is used.

FYI

https://www.youtube.com/watch?v=7T_HjZ49nFA

[madharchod]

shaft knuckles r we talking inboard outboard set up no this is outboard motor so no shaft knuckles its plain simple when the knock happens it wont go away so its the gears but if it goes away after a while as rpm increases its the plates on the impeller fitted wrong way replace it and no sound or knocking
sometimes after you drive the motor in sand and if your engines takes it sand and the impeller rubber grinds this sands onto the plates creating a seam and if this happens you will still get knocking sound at low speed but will disappear at high rpm
hope this helps