overheat-knocking noise

[Phantom17]

Looking at a boat. The owner says it developed a knock when (he thinks it was overheating). He shut it off for a minute, restarted. Knock still there, and had it towed in. Other than a circlation pump going south, what else might knock on a (possible) overheat? Not definately sure it overheated. <br /><br />Merc 3.0 Alpha 1, 1989

 

[whywhyzed]

Re: overheat-knocking noise

any number of bearings , especially a connecting rod bearing...<br /> a proper filter cutter like this can have you looking in the pleats. If a bearing is knocking, a magnet will pick "fur" out of the filter pleats (outside of the pleats)<br /> filter cutter pic <br /><br />I cut every filter coming off every engine with mine - helps for recycling the filter too...(and revealing which filters are utter crap..not naming framnames here)

 

[whywhyzed]

Re: overheat-knocking noise

and I meant to explain further.... over heat causes a normally round piston to distort and become "squarish", it then begins to seize in the round cylinder bore. As it seizes, it welds itself to the cyl. wall (adhesion). Then bits of aluminum will be knocked off by the rings, and into the oil (and the filter). With continued running, the piston may break, sending the now loose con rod flailing around and usually then "windowing" the block. But, if the pistons live, the contaminated oil finds it's way into the oil passages of the crank. Additional debris from bearings ends up clogging the lube passages. The con rod bearings are the last in line of the "cascade" delivery system. The brg. runs without lube until it begins adhesion with the crankshaft. The heat often causes the brg. to melt and it extrudes out of the journal and into the pan.<br />The pan removal is labour intensive to see the damage which is why a filter cut is done.

 

[rbezdon]

Re: overheat-knocking noise

I have also seen (or should I say heard) this from a blown head gasket (recent experience) and a exhaust valve not opening (old experience, rocker popped off on a car).

 

[KaGee]

Re: overheat-knocking noise

You have to hear it run yourself. Engine noises are funny sometimes. I have seen people describe knocks before, but it was really lifter noise.<br /><br />Another esteemed member recently thought he had a gear mesh problem with his distributor and cam because he heard a "whine". Turned out to be a vaccuum leak at the base of the carb.

 

[Boomyal]

Re: overheat-knocking noise

Originally posted by KaGee:<br /> <br />Another esteemed member recently thought he had a gear mesh problem with his distributor and cam because he heard a "whine". Turned out to be a vaccuum leak at the base of the carb.

Ahem!

 

[KaGee]

Re: overheat-knocking noise

Originally posted by Boomyal:<br /> Ahem!

<br /><br />Notice I did say "esteemed". <br /><br />

 

[Phantom17]

Re: overheat-knocking noise

It sounded like a spun bearing when "trying" to start, which it wouldn't start.......Another one left at the side of the road. To RI in the morning to look at the one with the improperly installed electronic ignition. Thanks, even as I pass these up, it's a good learning experiance. Thanks gents.

 

[Phantom17]

Re: overheat-knocking noise

I really like the boat too. The noise when turning the key was more of a whirring sound. The starter was also very slow. I was going to break out my jumper but I was a bit disappointed. <br /><br />Tell me, can the head of a 3.0 work on a 2.5 block? No square holes to round valves etc....