25HP Yamaha making a strange noise what is it??

[amit1978]

See attached video. It makes this noise in fwd, N and reverse but only when it is in water and not with ear muffs. It happened last weekend after 3 hrs of boating. Suggestions??

https://www.youtube.com/watch?v=ioLvOu_HpWk&feature=youtu.be

 

[robert graham]

Sounds sorta normal to me....but is your prop nut good and tight?....

 

[amit1978]

My motor was not making that rattle noise for 3 hrs while boating. Then suddenly it appeared. Also, it does not make that sound while running with ear muffs - its very smooth with ear muffs so it has something to do with the exhaust dipped in water. I will check the prop nut but would that affect the sound in neutral?

 

[schematic]

sounds like leaking exhaust. could be base gasket blown or corroded housing.

 

[robert graham]

My motor was not making that rattle noise for 3 hrs while boating. Then suddenly it appeared. Also, it does not make that sound while running with ear muffs - its very smooth with ear muffs so it has something to do with the exhaust dipped in water. I will check the prop nut but would that affect the sound in neutral?

I'm thinking that no noise on the muffs/ neutral/ prop not turning and then noise starts while in gear/underway it may be a prop/ lower unit....check prop for tightness....again, it didn't sound very unusual to me. Mine in a 1999 Yamaha C90 2 stroke and it makes some sounds/noise/rattles at various RPM's...just the music of a 2 stroke motor?....

 

[amit1978]

I would have thought the same if it made that sound all the time. It did not make that sound for almost 3 hours of continuous running. I recently bought this used and the previous owner is also surprised about this sound so I am wondering what could have caused it suddenly without anything unusual happening.

 

[robert graham]

Maybe operate the motor with upper cowling off to look/listen for source of sound?...

 

[amit1978]

Yes I did that. Seems to be coming from right on top - the flywheel perhaps?

 

[robert graham]

Could be a part or fastener loose under the flywheel....

 

[amit1978]

Mechanic checked it out and there was some water entering the lower unit turning the oil milky. There was also some melting found in the impeller housing. We have ordered these parts. The mechanic also said that if it was serious then it would happen at all speeds. So he is narrowing it down to the pull start assembly or the lower unit. I am waiting on parts to see if its any of these but just wondering could a water leak cause a sound like this? it did not sound like this for 3 hrs of boating and then this happened and even after that the performance did not go down.