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galynd · 24-08-2019, 14:37

I have a clattering problem with my yanmar 3gm30f on my beneteau 36cc. As I accelerate in forward, motor often shakes profusely at about 1400 rpms, then settles most of the time. Sometime I must go back to neutral then start over. I believe the sound is the shaft knocking on the shaft tube/log. I’ve read many entries similar to this and have tried all remedies but none have worked. The shaft also does not turn freely, by hand, when in neutral even when the couplings are disconnected. Basically, it is hard to turn with one hand. Further, as the motor warms the clattering is worse.

What I've done thus far with no success:
Aligned shaft, replaced one motor mount, replaced cutlass bearing, had prop checked out, adjusted valves, increased idle to 1000, had damper checked, replaced transmission with spare, replaced suction side fuel lines, replaced racor filter and water separator, by-passed the secondary fuel filter, temporarily replaced mechanical fuel lift pump with electric fuel pump, blew out fuel lines in tank (no sock) cleaned injectors with cleaner, removed injectors to have serviced. Shop said no service needed as they are perfect.

This started about a year ago and worsened slightly thereafter. About 2 months ago I pulled the boat and changed the cutlass and had the prop checked. The lip of the cutlass bearing was sucked inside the cutlass, or perhaps forced inside by fishing line, obviously causing friction.
I am starting to theorizing that when the new cutlass was put on, the two screws (top and bottom that hold it in place) were tightened excessively, creating the difficulty to turn the shaft, similar to the lips being inside the previous cutlass. The cutlass is solid rubber with lips that protrude.
Any thoughts on this puzzle are appreciated? See pic. Thanks, Greg