Mercruiser 4.3 LX weird engine noises. How to fix?

Fish-n-chicks

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Hi y'all,

New to inboard engines. By mere chance picked up a boat at an estate auction earlier this year. It came with a warning that engine needs work. It's a '96 Mercruiser 4.3 LX Gen + motor with Alphaone gen 2 drive. Engine runs but is making tapping noise. I was told by a friend it's just sticky valve lifters and engine just needed a good cleaning with seafoam treatment. Thought this could wait till the end of the season.

The motor had some milky residue in the engine oil at the beginning of the boating season when said friend changed oil. I kept checking dipstick but it looks clear after 10hrs on it. Engine starts with a bit of throttle when cold but runs fine and dandy and idles fine once warmed up a little. Took the boat out today and we were tubing when all of a sudden engine starts making new squeaking noises in addition to existing tapping.

Is the engine failing? What's the likely cause? Can I continue running it for a few more weekends and the look into it after the season? Or is it gonna seize/blow up on me any time now?

Also the boat seems to take on a bit of water when idling. I know I have the plug in tight. I have to run the bilge pump every 10min or so. Is the outdrive leaking?

EDIT: I think I posted this in the wrong forum.
 
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achris

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That engine sounds dreadful. The tapping is likely a lifter, the squeak could be anything. The fact that you've had water in the oil could mean a wiped bearing, or a stuffed camshaft, or anything else. First thing I would do is drop the belt and try and isolate the squeak. If it's one of the belt driven accessories, easy fix, if it's still there with the belt off, then it's internal, and probably terminal.

Chris......
 

midcarolina

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Sure don't sound good......... I agree with Chris remove the belt and see if you are lucky enough that it is something with an accessory......... You could also take a peice of tubing or pipe and make a poor mans stethescope put the tube to your ear and move around suspect area's of the motor the tube/pipe will magnify the sound and help you isolate the problem area.

I'm also guessing that the original tapping was telling you " hey I need attention " the continued operation likely made the problem worse, and further running will likely cause a terminal failure when you least need it to.......... unless it happens to be accessory related.
 

Fish-n-chicks

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If I pull the outdrive from transom assembly, could I replace the just the bellows? Besides the two bellows would I need new gaskets etc or could I re-use existing components?
 
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Fish-n-chicks

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I will pull the belt off tonight. See if that changes anything.

If it's not the belt and I were to pull the outdrive. According to video it pulls the drive shaft with u-joint out as well. Can I run the engine this way without damaging anything? This is to isolate the noise to the outdrive vs engine.
 
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Stamey

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If the engine is running then the shaft through the gimble bearing is turning, as well the vertical shaft in the stern drive. The neutral and forward/reverse happens in the bottom of the stern drive. That vertical shaft also runs the water pump in the stern drive so it must be turning at all times when the engine is running.
Yes, you can run the engine without the stern drive on the boat, but if you run it for more than a couple of minutes you must shove a water hose into the water inlet hole on the bell housing to supply the engine with cooling water.

Taking on water can be a multitude of things even if the transom is solid. Except for a leaking hole in the transom, such as for a depth finder or other intentional hole that is not sealed well, they will all be in involved with the stern drive. The first thing is one of the bellows. You have three, unless you have through-hull exhaust, and even then, a broken exhaust bellows won't let water into the boat. The shaft bellow, tiny, on the starboard side of the drive, will let water in, as well as the u-joint bellows, which is the largest, up high, centered in the drive unit. You will want to change all of these bellows when you get into it as a matter of prevention, since you do not know the age of what's on there now. It can make a difference as to whether the boat sinks. The bellows should normally last about 5 years.

The next possibility is the exhaust, but on the inside, where it connects to the exhaust Y-pipe. Follow the exhaust from your manifolds to the other side of the last set of rubber hoses (some setup have two sets, some have one set) on either side. If the seal between the Y-pipe and the transom bracket is bad it will leak into the bilge. Replacement, I believe, requires pulling the engine, because the bolts are very difficult to get to.

The next possibility is the rubber seal on the rear bracket for the stern drive. This is outside the transom, between the transom bracket and the hull. If this is bad you can temporarily fix it by running a bead of 3M '5200' sealant around the transom bracket where is joins the hull. I have been told the engine must be pulled to replace this rubber seal but I think it can be done just by loosening the transom bracket, if that's possible without pulling the engine.

Plan to change the water pump impeller and gimble bearing while you have the stern drive off as well.

Chris
 
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Bondo

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I will pull the belt off tonight. See if that changes anything.

If it's not the belt and I were to pull the outdrive. According to video it pulls the drive shaft with u-joint out as well. Can I run the engine this way without damaging anything? This is to isolate the noise to the outdrive vs engine.

Ayuh,..... Welcome Aboard,... Ya still gotta feed water to the motor or the rubber in the exhaust will burn up,.....

You can jamb a hose into the gimbell housin', or plumb into the t-stat hosin', where the in-comin' water enters the system,...
 
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Fish-n-chicks

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Removed the belt today.

No screeching/squeaking sound this time but the knocking sounds is def'ly there.

What could that knock be?

Thanks!
 
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midcarolina

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That's much more pronounced now......... I would pull the valve covers and see if it is a rocker, pushrod, or maybe a broken valve spring, If everything looks good up top, then it's something with the rotating assembly and motors gotta come out
 

Fish-n-chicks

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That's much more pronounced now......... I would pull the valve covers and see if it is a rocker, pushrod, or maybe a broken valve spring, If everything looks good up top, then it's something with the rotating assembly and motors gotta come out

If I pull the valve covers, would I need new gaskets for those?

How do you test a faulty pushrod or rocker? Will they be loose, discolored, bent? What do I look for?
 

midcarolina

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You will need new gaskets but hey are very cheap..........Look for anything that is noticably different from the rest of the parts......a broken rocker is easy to identify
A push rod could be bent, check for any an unusual amount of play when compared to the other rockers........

If the problem is topside it should be pretty obvious
 
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