Knocking noise at idle Yamaha 175

[Hoss IV]

Help!

I bought an Overnighter with a 1996 Yamaha 175. I had the boat professionally winterized and carbs redone. When the boat was splashed this year she knocks at idle (it didn't do this on sea trials prior to purchase). The knocking does not occur in neutral. Seems to go away at 900 rpm. The boat turns up fine with no slipping. Cruise at 3400 and can run WOT at 5400 with no problems. She still has a sticking float on the one carb.

Any ideas what this might be? I would hate to do any damage by running her.

Thanks!

CJ

 

[Hoss IV]

Re: Knocking noise at idle Yamaha 175

HEEELLLPP Anyone have any experience with this problem?

 

[JUSTINTIME]

Re: Knocking noise at idle Yamaha 175

if somebody fixed the carbs and still is sticking take it back

 

[Hoss IV]

Re: Knocking noise at idle Yamaha 175

Thanks. I did take it back....the float sticking doesn't scare me as much as the noise in clutch gear. Why would it make the noise in gear and not idling in neutral?

 

[Ray Neudecker]

Re: Knocking noise at idle Yamaha 175

It could be because of the prop or incorrect thrust washer. Failure to replace the bowl gaskets or needles is the primary reason for intermittent needle sticking

 

[Hoss IV]

Re: Knocking noise at idle Yamaha 175

thanks for the comeback. What is the thrust washer? It didn't make this noise during the sea trial, only after the shop did the water pump. There are some slight occlusions to the stainless wheel...I mean minor.

 

[gcboat]

Re: Knocking noise at idle Yamaha 175

Your thrust washer goes on your prop drive shaft. It's a big round piece of metal that keeps the prop from wandering fore and aft on the shaft. Call it a spacer if you will. Check your connecting bolts on the lower unit, check and match your serial number on the unit as well.

 

[Osprey]

Re: Knocking noise at idle Yamaha 175

Hoss IV,

I have a 95 175 on a Grady 208. Shortly after I bought it, the motor developed a knock much like you describe. Thought it was a main bearing for sure but it proved to be a brass bushing that the upper end of the main shaft rides in.

With the lower unit removed, if you look up into the mid section, the bushing is the first opening that the main shaft would enter as the lower unit is being installed. The bushing is rubber coated and is retained by a large C-Clip. It can be removed without the need of a puller or any special tools. I now always grease the main shaft on the bushings mating surface prior to installing the lower unit.

A second possible cause? Being you just had your impeller serviced, I thought of this. Believe that starting in 95, Yamaha added what they call preload washers to the impeller assembly. This was to correct an issue with chatter and knocking sounds caused by the impeller. When your impeller was replaced these washers may not have been properly reinstalled. Maybe Ray could help with this as I'm not sure what sound this would make or when. Seems like it might only knock when the motor is first put in gear.