weird screeching noise 3000 RPM and above MERC 470

L

lselmes

Seaman Apprentice
Joined
Sep 21, 2006
Messages
31
I have a smooth running 1981 Mercruiser 470 that runs cool and has good pressure on all cylinders as well as oil. The last 2 trips out I've had a strange intermittent screeching sound coming from the motor when I hit 3000 rpm and above. Alternator belt looks good and I haven't confirmed the alt bearing yet. I did just have a new Mallory E-Spark electronic ignition installed and the mechanic had to mess around with the distributor to install a mounting plate. Do distributors make a noise if not installed properly? My voltage is steady with no fluctuations. And as I said the motor performs beautifully except for this awful new noise. Any input would be much appreciated.

Cheers!
 
S

stonyloam

Vice Admiral
Joined
Mar 13, 2009
Messages
5,827
Re: weird screeching noise 3000 RPM and above MERC 470

The power steering pump can make a similar noise.
 
Fishermark

Fishermark

Vice Admiral
Joined
Oct 19, 2003
Messages
5,617
Re: weird screeching noise 3000 RPM and above MERC 470

Run it briefly without the front belt and see if the squeal goes away. Also feel the bearings on the water pump to see if it turns smoothly. Do you have the alternator conversion for this engine?
 
S

stonyloam

Vice Admiral
Joined
Mar 13, 2009
Messages
5,827
Re: weird screeching noise 3000 RPM and above MERC 470

Fishermark said:
Run it briefly without the front belt and see if the squeal goes away. Also feel the bearings on the water pump to see if it turns smoothly. Do you have the alternator conversion for this engine?
Click to expand...

That is a good idea, however there are no bearings in the waterpump, and you may run it as long as you like without the power steering/alternator (if you have one) belt on, because the engine waterpump impeller is bolted to and directly driven by the camshaft.
 
Fishermark

Fishermark

Vice Admiral
Joined
Oct 19, 2003
Messages
5,617
Re: weird screeching noise 3000 RPM and above MERC 470

stonyloam said:
That is a good idea, however there are no bearings in the waterpump, and you may run it as long as you like without the power steering/alternator (if you have one) belt on, because the engine waterpump impeller is bolted to and directly driven by the camshaft.
Click to expand...

Oops - yep. I forgot about the circulating pump arrangement.
 
G

generator12

Senior Chief Petty Officer
Joined
Jul 9, 2010
Messages
666
Re: weird screeching noise 3000 RPM and above MERC 470

There's also the old trick of quieting a slipping belt with some belt dressing. Using it once for testing purposes shouldn't have any negative effects.
 
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