"Blown" 1983 Mariner 150 XR-2 Marathon Magnum V-6

I have a very loud knocking sound coming from my motor. Happened suddenly. Motor restarted and was able to idle for 5 minutes back to dock.

Due to the expense of professional repairs and the lack of money for this repair, I am going to try to fix it myself. I have some experience with motors, but should be considered inexperienced with internal type repairs. I have isolated the cylinder by holding my thumb over the spark plug ports. Once cylinder has no compression that I can feel.

Assuming it is a broken/bent rod, rings, etc., what would most likely cause this to happen. I premix my fuel, use the best oil and additives I can, and I take care not to run the motor harder then I need to for the fishing I do. Bought this boat for almost nothing and the motor has always run well for me.

I will post more after taking the head off tonight to see what I can find out.
Thanks for any help and advice. Great forum from what I have read so far.
Chieftain

Re: "Blown" 1983 Mariner 150 XR-2 Marathon Magnum V-6

Chief, Normally the cause for ring failure is lean running or overheating. Knocking could indicate something else. Let us know what you find and post some pics....

Re: "Blown" 1983 Mariner 150 XR-2 Marathon Magnum V-6

Chris,
The #2 piston was a mess. All the others looked ok so far. I took both heads off when I saw the port side. Figured if I was going to buy a gasket set, I might as well check everything so I can avoid doing this all over again. I will try to attach pics so you can see what I am dealing with.

I ordered the manual for this motor and I am hoping it gets here today, but I don't expect it will. I am not totally sure about my next step as far as removing the front of the block (don't know the technical term), so that I can get at the rods to release that piston.

Any suggestions on why this may have been running too lean? Also, can this much damage have been done in such a short period of time? I ran the boat for several hours on Lake Erie on Thursday with no problems. Ran smooth, lots of power, etc. On friday, I ran it at full speed for less than a minute after a good warm up at idle and 25% throttle. It lost power very quickly and started knocking. I idled to the dock for less that 5 minutes and shut it down.

Thanks for your interest in my project.
Chieftain

Re: "Blown" 1983 Mariner 150 XR-2 Marathon Magnum V-6

You will need to pull the powerhead to get at the crank and rods. Pull the gearcase first to make reassembly easier. Maybe your head gasket was bad, allowing water to reach the cylinder?