Loud knock at high RPM on Merc 7.4L BII

Annata

Member
Joined
Jul 7, 2006
RO Number
22225
Messages
1
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Engine runs smoothly and quietly up to about 3800 rpm, then gets a tremendously loud mechanical knock. There are 600 hours on the engine, good temp, pressure, belts, etc. Freshwater cooled, well maintained. Lives in freshwater, ventures to salt occassionally.
The knock is not rhythmic - it is about every 2-3 seconds.

The boat is a 1996 2858.

Thoughts?
Thanks for the help!
 
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