Yamaha 4 stroke 115 lower unit knocking when cruising and idling

showard93

Recruit
Joined
Jul 19, 2013
Messages
2
I recently noticed a knocking sound coming from the engine while cruising. I dropped the lower unit and found no water in the gear lube (it was deep blue in color). I did, however, have some metal shavings on the drain plug. I've read that some shavings are normal but I'm not sure what would constitute too many. I went ahead and changed the impeller and replaced the washers. I ran the engine with water hose attached, and the lower unit is still making a knocking sound. A couple of years ago I hit something with my prop and had to have it repaired....it was slightly bent. I haven't had any other problems until recently. I was running at full speed when I first noticed the sound and it was at first a random knock. Based on what I've read, it sounds like I could have a bearing that's gone out or maybe a gear issue. I would like to take the boat out this weekend to see if it is still making the sound at full throttle but I don't want to make the issue worse. Any advice?
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Re: Yamaha 4 stroke 115 lower unit knocking when cruising and idling

Did you pull up on the driveshaft while forcing that collar and wave washers down to remove drive line up and down slack to prevent knocking?....just a thought...good luck!
 

Toddboat

Petty Officer 2nd Class
Joined
Jun 13, 2013
Messages
134
Re: Yamaha 4 stroke 115 lower unit knocking when cruising and idling

I read on this blog somewhere that people with stainless steel props can get gear damage when they hit something because the prop doesn't break/bend as easily as the aluminum ones do. The aluminum ones sacrifice themselves, whereas the SS props sacrifice the teeth on your gears instead. Just a thought, you may want to research some of the posts on here about the SS props.
 

showard93

Recruit
Joined
Jul 19, 2013
Messages
2
Re: Yamaha 4 stroke 115 lower unit knocking when cruising and idling

Thanks, I'll give this a try. Can anyone tell me what too many shavings is on the drain plug?
 
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