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Old 06-20-2011
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Bumping/Thumping Noise-Advice Needed

Could use a little advice here -- I've got a 1980 Volvo MD7A that I'm worried about. When in gear, there is often a low tone thumping or banging sound that seems to be coming from the rear of the boat, but I can't pinpoint where. The thumps are rhythmic, about 3 or 4 a second. The thumps will vary in volume, will be loud for a few seconds then quiet down a little. I've heard these thumps before, noticed them most when in waves (figured it was water covering the exhaust port, which is right at the waterline and easily submerged). But the thumps seem to be worse now and happening all the time. I can feel the thumping in the hull, it's almost like someone is hitting the hull with a rope or something. Increasing throttle increases the volume of the thumps but rhythm stays the same.

The engine itself seems to run fine, plenty of power but now it is generating grey/white smoke at higher RPMs which I did not notice before. I just hauled out by the way, and cleaned the prop, shaft, installed new zincs, oil change, impeller change.

Please advise, I'm about to leave on a week long trip. Is this potentially damaging to the engine to run it this way? My gut tells me this is an exhaust issue ("water hammer?") Thanks!
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1980 S2 9.2A (30') in Anacortes, WA
Aux power 13hp Volvo MD7A

Last edited by FishFinder; 06-20-2011 at 02:49 AM.
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