Growling Merc 20 hp

[Jake N]

I have a '76 model, 20 hp Merc that I bought used last year.

The motor runs real loud with a growling, rock chewing sound. I thought that this was the way the old motor was supposed to sound until recently I noticed it would get super-quiet for short periods of time.

The motor makes the noise both while it is in and out of gear. It goes silent for brief periods of time while running a constant rpm.

It runs pretty strong but the power does seem to fade on occassion. I can't link the power fade to a difference in noise though.

The motor cranks fine.

It has made this growling, rock grinding noise for a whole year without breaking anything.

Bearings bad? Exhaust noise? Other?

I often believe that the best method of troubleshooting is to wait until it breaks and this looks to be one of those occassions.

I know I'm not giving a whole lot of details but I appreciate the help.

 

[8075mercury]

Re: Growling Merc 20 hp

My vote would be to figure out what the noise is before it tears something up.

Assuming the compression is good and the lower unit oil looks clean, I would pull the pull start off (assuming you have a pull start) and see if the starter pawls are not fully retracting and banging against the flywheel. You might try carefully starting it with a rope with the pull start off too and see if the noise changes. Or, run it with the cover off and see if you have a loose piece banging somewhere.

Just a guess, hope you find it.

Good luck, these are great motors!

 

[Jake N]

Re: Growling Merc 20 hp

I'm inclined to believe it's an exhaust problem although I don't have much to base that on. The exhaust is routed via a tube from the power head to the foot but the sound sounds like the exhaust is escaping before the foot.

I don't think it's the recoil starter because occassionally the recoil starter will get pulled on while the motor is running and it will make an entirely different sound.

My sound is a deep, loud, gutteral growling. You can barely talk over the sound of this motor when it is 1/3 throttle. You have to raise you voice.

 

[Jake N]

Re: Growling Merc 20 hp

No other thoughts?

Can someone confirm for me that an exhaust leak can be intermittent?

 

[Jake N]

Re: Growling Merc 20 hp

Anyone? Intermittent, loud ,growling noise, no apparent loss of power, loud most of the time but gets ultra-quiet for brief periods, does this in and out of gear, gone through several tanks of gas and nothing has broke yet. Anyone?