4.3 l mercruiser knock at idle forward and reverse

Kikibear097

Recruit
Joined
May 6, 2020
Messages
2
I have a 4.3 mercruiser alpha gen 2 . It is knocking and has a high pitch squeak or squeal. Need help. Was on the water at 3000 rpm heard a loud knock and oil pressure dropped. Check everything when we got home and oil is good pressure is good but on now has a knock. Any help would be great
 

Rick Stephens

Admiral
Joined
Aug 13, 2013
Messages
6,118
Sounds like a rod bearing is totally toast. You may be able to pull plug wires and determine which one, but it won't matter, needs to pull motor and tear it down.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,365
pull the drive, then run it for a bit. could be really really sloppy u-joints slapping around. (possible, however most likely the rod bearing)

if not, you need to pull the drive anyway to pull the motor
 

Bt Doctur

Supreme Mariner
Joined
Aug 29, 2004
Messages
19,453
Has the sound of a loose rocker or collapsed lifter. In the first vid the knock stopped as rpm was increased. After verifying rockers and pushrods the suspect a bad rod .Pulling the spark on the offending cylinder will help identify it.
 
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