Mercruiser 3.0 Engine knocking noise

[tony.lewis411]

I have a knocking noise and can't determine where it's coming from. Little history - I had the lower unit impeller go bad and it over heated the engine. I pulled the head and had it checked because water was getting in the oil. Head checked out good and I replaced the head gasket of course. Still getting water in the oil. I replaced the exhaust manifold gasket and elbow gasket and the water stopped getting in the oil. Ever since then I have had this knocking noise and I cannot figure out where it's coming from. I just had it tuned up and the valves adjusted and that was not the problem. It has been running like this for almost 10 years and the noise has not gotten better nor worse. Any input would be greatly appreciated.

 

[Scott06]

I have a knocking noise and can't determine where it's coming from. Little history - I had the lower unit impeller go bad and it over heated the engine. I pulled the head and had it checked because water was getting in the oil. Head checked out good and I replaced the head gasket of course. Still getting water in the oil. I replaced the exhaust manifold gasket and elbow gasket and the water stopped getting in the oil. Ever since then I have had this knocking noise and I cannot figure out where it's coming from. I just had it tuned up and the valves adjusted and that was not the problem. It has been running like this for almost 10 years and the noise has not gotten better nor worse. Any input would be greatly appreciated.

Can you narrow down where the noise is coming from?

have you run it with out the drive and taken the belts off to see if it is an accessory or water pump, gimbal bearing ujoint etc? Flywheel loose?

Would spend some time trying to figure out where it it coming from - loose rocker ?

 

[ScottinAZ]

Can you narrow down where the noise is coming from?

have you run it with out the drive and taken the belts off to see if it is an accessory or water pump, gimbal bearing ujoint etc? Flywheel loose?

Would spend some time trying to figure out where it it coming from - loose rocker ?

second this.... it doesnt sound like a rod knock, it sounds more accessory or drive related to me.... but we cant tell really in a video....

 

[kenny nunez]

If I read your description right you stated that this noise has been present for 10 years? Or has it started as a result of water entering from the manifold?
The engine appears to be idling rougher than normal. 3.0s normally idle slightly rougher than a 2.5.
It almost sounds like the rear engine mount insulators are pounded out and there is metal to metal contact.

 

[kenny nunez]

If I read your description right you stated that this noise has been present for 10 years? Or has it started as a result of water entering from the manifold?
The engine appears to be idling rougher than normal. 3.0s normally idle slightly rougher than a 2.5.
It almost sounds like the rear engine mount insulators are pounded out and there is metal to metal contact.

 

[Scott06]

If I read your description right you stated that this noise has been present for 10 years? Or has it started as a result of water entering from the manifold?
The engine appears to be idling rougher than normal. 3.0s normally idle slightly rougher than a 2.5.
It almost sounds like the rear engine mount insulators are pounded out and there is metal to metal contact.

One I didn't think of - can you check with a pry bar ?

 

[airshot]

Check for a cracked block if water is in the oil...did you check how flat the deck ( block) was before putting the head back on ?? 3.0 heads are known for warping under overheat conditions but the block deck can also be out. Usually shows low compression on #2-3 if a warped head or deck. Did you replace exhaust shutters after overheat?? If not, probably needs them, they can cause a knock when loose or burnt.

 

[tony.lewis411]

Thank you for all of the suggestions. It sounds like it's coming from the front of the motor. I have not tried to run it without the belt on but that was suggested by someone else so I will try that this weekend. I will also check the motor mounts as I have seen other posts about this causing a very similar sound. I believe the sound started after the water got into the oil and it's been running like that for close to 10 years. I will check these things this weekend and report back what I found. Thank you all again for the suggestions

 

[Scott06]

Thank you for all of the suggestions. It sounds like it's coming from the front of the motor. I have not tried to run it without the belt on but that was suggested by someone else so I will try that this weekend. I will also check the motor mounts as I have seen other posts about this causing a very similar sound. I believe the sound started after the water got into the oil and it's been running like that for close to 10 years. I will check these things this weekend and report back what I found. Thank you all again for the suggestions

the front of the motor items are water pump, gear drive for cam shaft, fuel pump, cam and lifters are accessible on starboard side behind covers.

Any of those items could be damaged by lack of lubrication due to water in oil.

 

[ROY WILLIAMS]

The water sealer is worn out ...engine oil of the water .....

 

[tony.lewis411]

Here is a picture of the rear engine mount bolt. Both sides look the same and it appears to be backed out. This side looks to be out farther than the other side. I'm guessing it shouldn't be like this?

 

[Scott06]

Here is a picture of the rear engine mount bolt. Both sides look the same and it appears to be backed out. This side looks to be out farther than the other side. I'm guessing it shouldn't be like this?

No there is a sleeve under the bolt like that this looks correct .

 

[04fxdwgi25]

With the double knock, sounds like a piston / connecting rod trying to escape. With all that shaking, I would do a compression check.

 

[kenny nunez]

I am beginning to think that the flywheel might be loose. I cannot imagine an engine making that much noise for that long without finally coming apart.

 

[tony.lewis411]

With the double knock, sounds like a piston / connecting rod trying to escape. With all that shaking, I would do a compression check.

The mechanic did a compression check and 3 are at 120 and 1 is at 135

 

[Scott06]

I am beginning to think that the flywheel might be loose. I cannot imagine an engine making that much noise for that long without finally coming apart.

agreed, but also would think the flywheel would come off over that time ?

 

[tony.lewis411]

I believe the noise started after I noticed water in the oil after overheating. I fixed the water issue. Is there internal damage because of water in the oil

 

[Scott06]

I believe the noise started after I noticed water in the oil after overheating. I fixed the water issue. Is there internal damage because of water in the oil

It’s not uncommon for engines to start making noise after getting hot. Water in the oil never helps. As the group has mentioned there are a few items to look at otherwise pull the engine and tear into it.

 

[kenny nunez]

If the noise leaves when there is a load on the driveline then that would indicate a flywheel problem. However if it remains with or without a load then it could a cracked piston skirt or a wrist pin. Most times a cracked piston skirt eventually comes apart but a wrist pin usually does not. Since water does not compress, then it must be piston related since you stated it started with water in the oil.

 

[Silvertip]

Post another video showing the engine being slowly increased in RPM to 2000 - 2500 rpm. Piston slap or timing component slop sometimes disappears at off-idle. I've seen the small fuel pump lever return spring break and the engine torn down needlessly because of it. Makes a horrible sound. Excess slop in the timing gears would show up as noise up front. Broken piston skirt makes a rod knock sound and a bore scope check of cylinder walls would probably show scuffing.