Mercruiser strange sound at higher RPMs


Old 04-24-01, 06:25 PM
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I have a 1998 bayliner 2052 with a 4.3L Merc I/O tied to an Alpha I outdrive. At and above 2900 RPM I get a loud, metalic, sound that cycles (bang, bang,...) If I run the engine without the drive engaged, above and beyond 2900 RPM, the sound is not there. When I run the engine on the trailer and put the drive in gear, again, above 2900 RPM the sound is not there. It appears the sound only occurs when there is a load on the engine/drive. I have had the prop looked at, and there appears to be nothing wrong. The engine was just re-built last summer and does not appear to be the problem. Could it be the gimbal bearing or U-joints? If so, is this something I can replace? Thanks.
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Old 04-24-01, 07:31 PM
BoatMech's Avatar
Join Date: Dec 1999
Location: Los angeles
Posts: 592
Banging sounds are not good.
We need to know if it is erratic or a rythmic beat.
The fact that it is less noticable under load
leads me to universal joints. I wouldnt rule
out though that it may just be bad flapper valves
in the exhaust. they have an erratic metallic slapping
sound at idle and go away at high rpm.
In any case pull the drive and check the u joints.
Its easy and good insurance. Lube the gimbal brng too.

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