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Noise in my engine compartment

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billmay

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I have a 3.0 omc. Around 800

I have a 3.0 omc. Around 800-900 rpms there is a metallic sound coming somewhere in the engine compartment. You don't hear this sound at idle or 1000 rpm and above. I can't find any loose items on motor. This noise is real bothersome. Appreciate any help. Tanks
 
" Not sure but ~~~~ Run engine

" Not sure but ~~~~ Run engine to RPM where noise is loudest , use a steel screwdriver or whatever as a stephiscope , one end at your ear the other place on or near the exaust elbow. If noise is louder here that at different areas your problem is worn out shuttle valves. The sutttle valves are rubber flaps installed in ex. pipes to prevent water from flowing back up the ex. tube ~ over the riser and into the Ex. manifold in a heavy stern wave situation.
The fix is quite simple but requires removal of Ex. elbow to access valve.
Suggest not to ignoir replaceing it as it has been known to happen where the stainless steel pin that the rubber flappers hindge on has fallen down into Ex. tube and after time has caused corrosion (stainless steel vs. alum. ) severe enough to put a hole in the Ex. tube which ofcourse is well below the water line. "
 
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