Yamaha 50 hp knocking

[Fred Tanguay]

I got a yamaha 50hp that are making a knocking noise when i go fast on reverse. If i go slow, it's ok, but when i increase the rpm, it start doing it. The engine have always been doing that, but lately, someone told me it's not normal.

Is anybody notice that on it's outboard also or knows what could be the problem???

Thank you

 

[99yam40]

you need to find out where it is coming from.
Power head or lower unit

 

[Fred Tanguay]

Its coming from the lower unit...

 

[99yam40]

I cannot think of anything that would cause a knock in the lower unit just in reverse under heavy throttle.
What is your model # and year and has any work been done on this lower unit?

 

[pro-crastinator]

Google and purchase a mechanics stethescope for $3. It helps - a lot.

http://www.harborfreight.com/mechanics-stethoscope-69913.html

 

[Fred Tanguay]

My engine are a f-50 from 2006 and i can't use a stehtoscope because it's only doing this knock when im giving more throtle on reverse when the boat are in the water.

It's making that knock every 2-3 second.

Could it be a kind of safety that advise when im giving to much throtle on reverse??? Just like a kind of cut out.

 

[Fred Tanguay]

The lower unit have never been opened and i never find any metal parts on the magnet on the lower oil plug.