Thunk and a lurch.... what could it be?

rnourse

Cadet
Joined
Aug 5, 2012
Messages
10
I have a 1987 Bayliner with the 2.3L OMC + Cobra sterndrive. Generally its been a terrifically reliable engine but I've learned to pay attention when it starts making noises. Like last weekend when we noticed something new.

Every once in awhile (say 5-10 minutes of operation but growing in frequency) the boat will make an audible thunk noise while we're cruising. At the same time the boat will lurch slightly as though you've hit something like a log in the water. Over the course of the weekend we've noticed this went from once on friday to once every 5-10 minutes of operation on sunday. We stopped using the boat the moment we realized this was happening but I'm at a loss to guess what it could be (or more importantly how much it could be!). I'm guessing its transmission related as the mounting seems secure and the transom appears intact.

Anyone have any suggestions?
 

Idlespeedonly

Senior Chief Petty Officer
Joined
Jun 30, 2011
Messages
779
Re: Thunk and a lurch.... what could it be?

The clutch dogs are probably shot. A cable adjustment might get a little more life out of it. But more than likely time for a rebuild.
 

rnourse

Cadet
Joined
Aug 5, 2012
Messages
10
Re: Thunk and a lurch.... what could it be?

Fair enough... any idea of how major or minor a piece of work that is?
 

davesissom

Cadet
Joined
May 26, 2013
Messages
14
Re: Thunk and a lurch.... what could it be?

Replace the shift cable, that's what caused this this, or its out of adjustment. Mine did the same thing and I could hardly get it on the trailer at idle. My slip clutch(dog clutch) was bad and the cable caused it. hopefully you didn't mess up the gears (I didn't) Replace the cable and prob. the slip clutch. (couple hundred plus labor). If you use it gears will go bad quickly. They are about 500. Good Luck!
 

Idlespeedonly

Senior Chief Petty Officer
Joined
Jun 30, 2011
Messages
779
Re: Thunk and a lurch.... what could it be?

The other thing that causes this is shifting into gear slowly. Whenever you hear rapid clicking when shifting, you are shifting to slow.
 

rnourse

Cadet
Joined
Aug 5, 2012
Messages
10
Re: Thunk and a lurch.... what could it be?

Tx guys... Boat is at the mechanics. Ill report back with the damage when it's over :(
 
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