4.3 Mercruiser Noise

[JasonB]

Helping a friend with a 1990 4.3 Mercruiser. Motor history is unknown, but was supposedly rebuilt a year or two ago. Starts and runs ok, but has a loud ticking/knocking accompanied by a loud metal on metal sskreak/scraping that starts about 30 seconds after starting. Tick/knock is very rythymic and seems to be at the rate of the valve train. Both get much worse with throttle. The scraping sound comes/goes a bit.

So far, we have removed the belts to isolate the PS pump, water pump, and alternator - no change. Pulled the valve covers to watch the action, and it seems to be ok, but it seems to take longer than I expected for oil to come out of the pushrods. Pulling plug wires one at a time doesn't seem to make much difference

I have to check with my stethascope, but I can't isolate the knock to either head, but it seems to echo all around the engine. The engine does not seem to have a miss.

The metal on metal "scraping" that starts about 30 seconds after startup is the one that has me most puzzled.

Any other ideas before teardown?

 

[Bondo]

Re: 4.3 Mercruiser Noise

Ayuh,... Donno what you've got goin' on, But...
I pulled a 4.3l a few years ago with Bad sounds,...
The crankshaft was broken clean off in the center bearing...
It ran just Fine, but the crank was broken clean in 2 by a bottom strike the fall before...

 

[zbnutcase]

Re: 4.3 Mercruiser Noise

Check to make sure outer ring of damper hasn't came loose and moved backwards to rub on timing chain cover.

 

[cr2k]

Re: 4.3 Mercruiser Noise

Have you tried pumping some grease in the gimbal brg? If it is bad the noise can transmit to the engine and sometimes be hard to isolate. If no luck pull the drive and see if the noise goes away.

 

[kewlkatdady]

Re: 4.3 Mercruiser Noise

sounds like an engine not getting lubricated properly....

the whining noise reminds of dry bearings... the rhythmic ticking is more than likely valve noise

Hopefully I'm wrong as if I'm right...get ready for a rebuild.

 

[JasonB]

Re: 4.3 Mercruiser Noise

Thanks for the replies. I did a compression check and the results were't promising: (1-6) 125, 145, 115, 125, 145, 145. Suspected a blown gasket between between 1 and 3. Not sure about 4 as it is in the middle of the other side, Plugs were all dark. Found some evidence of water in the oil. Oddly, oil on the dipstick looked clean, but the water coming out of the pushrods looked like milkshake. Pulled head for 1-3-5. All I got was a somewhat stripped metal gasket. The sealing material stuck to either side. The exhaust gasket was the same way. Piston 3 was wet/oily, the stern side of 1 was wet/oily. The same wet/oily residue showed on the block between 1-3. #5 looked perfect. Haven't pulled the other head yet.

water flow out the prop/idle reliefs before teardown didn't look right. Suspecting this thing was run hard + put up wet and overheated. The very dark LU fluid seems to support my theory of "put up wet".

Owner is looking for a new longblock from a truck, maybe a Vortec. That may be a better bet than a rebuild. This motor was supposedly rebuilt sometime before last year. Good thing he bought this boat with the assumption of replacing the motor.

Now to get the transom, out drive, and trailer in shape while we figure out a powerplant. Pulled the drive to find a u-joint bellows full of water and a bad gimball bearing. Time for bellows, gimbal, u-joints, and water pump rebuild.

 

[JasonB]

Re: 4.3 Mercruiser Noise

Just another update.

Pulled the head for 2-4-6 off last night. Found the source of the noise and confirmed more of my overheat theory. Pulled the head off and a piece of impeller was sticking out of one of the water passages by #4. A look at the piston and head in #4 shows that the piston was touching the head. I'm guessing this is likely a spun or otherwise damaged bearing and the screeching noise is likely related. Cylinder walls look ok from what little I can see, but who knows what's lurking under the piston which it not far from TDC. On to the newer Vortec motor....

 

[mj05]

Re: 4.3 Mercruiser Noise

Holy Smokes!! this thread made me cringe the whole way through! Keep updating, I'm intrested to see what ends up!

 

[Squab]

Re: 4.3 Mercruiser Noise

l have the same engine.. Should I hear any taping coming from the valve area? I not having problems but this post makes me think

 

[JasonB]

Re: 4.3 Mercruiser Noise

I'll post up when I take the motor the rest of the way out in a few days and pull the pan. He was hopeful it would be fixable, but my advice before he bought it was to assume replacement/rebuild. I suspect the crank will be toast. It really amazes me how bad this motor was abused and still running reasonably well(except for the noise). It idled with almost no shake and started right up......

In general, you shouldn't hear any major tapping noises from a healthy motor, although the 302 I run *almost* sounds like it is tapping but is really a rythymic whooshing, but it is just the way this motor sounds as it has done it for 8 years and 300+ hours. Keep in mind that there is evidence that this motor was severely overheated. I'm guessing the overheat caused the bearing failure, and subsequently the tapping and skreeking.

 

[kewlkatdady]

Re: 4.3 Mercruiser Noise

with the pieces of impeller you found...
overheating sounds very plausible...

 

[Squab]

Re: 4.3 Mercruiser Noise

Can I just take the Valve covers off and start the engine or will oil come shooting out?

 

[Bondo]

Re: 4.3 Mercruiser Noise

l have the same engine.. Should I hear any taping coming from the valve area? I not having problems but this post makes me think

Can I just take the Valve covers off and start the engine or will oil come shooting out?

Ayuh,.... 1st thing you can do is,....
Start your Own thread, instead of Hi-jackin' Jason's thread....

 

[4Winns2]

Re: 4.3 Mercruiser Noise

I too am interested to learn what you find out. I've got a tick, tick, tick going on at the back of my 4.3 OMC. It doesn't sound (I stuck my ear everywhere in the engine compartment) as if it's coming from the engine but rather from the back of the engine to the transom. I noticed it in the spring when I put her in but didn't hear it that much, if at all, during this past season where I put some major hours on her. The tick, tick, tick, seems to make the engine skip at idle too. It's befuddling and I'd like to narrow the issue down if I can. I'll be keeping an eye on this thread. Thanks.

 

[JasonB]

Re: 4.3 Mercruiser Noise -Update 11/10

Re: 4.3 Mercruiser Noise -Update 11/10

Here's your latest installment of as the motor turns, errrr. doesn't turn.

pulled the rod bearing and pistons from the old motor. In the words of a great fellow, It's bad Andy, Real bad.

#1 and 2 not too bad but the rods were loose on the crank from bearing wear. #3 bearing was cut up badly and was worn in a trapezoid shape and the journal is damaged. #4 is a basket case. Metal on Metal, no bearing left, crank and rod damaged. #5 and 6, not too bad, but worn. #3 and #4 rods show signs of high temperature discoloration. Showed signs of what I think is oil starvation and debris in the oil.

Haven't pulled all the mains/thrust yet, but #2 and #3 mains have scoring on the bearings. Saddles and journals seem not bad.


So here's my theory..... Something caused a spun bearing in #4, likely overheat and they kept running it for a while. #4 bearing came apart sending metal everywhere damaging other bearings/journals. I'm thinking everything in this motor is suspect with the possible exception of the block itself.

Newer vortec donor motor has issues as well. One head is trashed with a crack. Looks like teh short block needs to come apart for closer inspection. The rods and block are brown so I wonder if it was overheated as well.

 

[Bondo]

Re: 4.3 Mercruiser Noise -Update 11/10

Re: 4.3 Mercruiser Noise -Update 11/10

So here's my theory..... Something caused a spun bearing in #4, likely overheat and they kept running it for a while. #4 bearing came apart sending metal everywhere damaging other bearings/journals. I'm thinking everything in this motor is suspect with the possible exception of the block itself.

Ayuh,... Sounds like an Anchor to me...

I agree with your theory,... #4 is the 1st in the flow, it's Junk went to the others...

 

[JasonB]

Re: 4.3 Mercruiser Noise

Here are some pics. In order they appear,
Rod journals #1 and 2 + main 2,
rod journals # 3 and 4 + mains 2 and 3,
Rod journals 5 and 6 + Main #3, #3 bearing piston side - hard to tell in the pic, but the bearing is "cut" in a trapezoid shape like it came out of its groves,
main bearing #3 + other half of rod bearing #3 - note the sliver of metal hanging off the side

Except for the tapping/screeching, the motor idled smooth with very little shake. This thing was abused badly.