1991 OMC Cobra 4.3 engine knocking noise

[boatmann]

I just bought a the boat mentioned in title. We test drove it and it ran fine. I bought it and replace plugs etc. The one plug I took out water came out. I took boat out again ran great. Now on vacation with the family and took boat to lake and started it at ramp and a knocking noise was coming from engine. So I pulled boat back out. I am wondering this is only the 3rd time out since winterizing boat, the first 2 times the boat ran great then this time it sounds like a rod knocking. How would it run great and then this happen? So, is it a cracked block or something else?

thanks

 

[Bondo]

Re: 1991 OMC Cobra 4.3 engine knocking noise

The one plug I took out water came out.

Ayuh,... At that point, Something is horribly Wrong...

My guess is, a cylinder filled with water, 'n the starter was strong enough to bend a rod, shoving it through it's cycle...

 

[boatmann]

Re: 1991 OMC Cobra 4.3 engine knocking noise

Thanks for the reply Bond-o, I just don't see how it could run so good after I put the new plugs in. I ran it for at least an hour. But, with that knocking it does sound like a rod. So, complete rebuild?