Motor knocking. Mercruiser 3.0 alpha 1

[eriewalleye]

Was hoping for a little advise here. My motor is knocking from the front lower end only after warm up. I put my stethoscope on the motor and it is loudest right behind the harmonic balancer on the cover plate. Motor is run on ethanol free 93 octane gas. Oil and filter have been changed. Using 25w-40 as recommended. Levels are good and oil pressure is around 40 psi while running in neutral at 2000 rpm. Wishing i had saved the old filter and checked it for metal debris. I am some what new to boating and as the season is coming to an end I wanted to play it safe and no longer run the boat. As an amateur I'm trying to not go down the rabbit hole of rod knock/bearing issues though I am beginning to suspect this. If you motor needs pulled better now as winter is coming and I can be back up and running for fishing in the spring. Below is a video of the noise I am experiencing. Any advice would be greatly appreciated!

 

[Scott Danforth]

Pull the drive and check. If knocking continues, pul the motor

 

[Grub54891]

Sounds alot like mine. I figure if it blows it's no big deal on it. it's my beater boat that only stays on a lake only a mile and half big. 350 acre lake. I'm thinking it's lifters, but on by rebuild boat I found the fiber cam gears were missing half the teeth. This coming spring I'll investigate as it's time for a major tune up. Hope you find the issue, would help me in diagnosis.

 

[eriewalleye]

Sounds alot like mine. I figure if it blows it's no big deal on it. it's my beater boat that only stays on a lake only a mile and half big. 350 acre lake. I'm thinking it's lifters, but on by rebuild boat I found the fiber cam gears were missing half the teeth. This coming spring I'll investigate as it's time for a major tune up. Hope you find the issue, would help me in diagnosis.

I will keep watching this page and post when I find the issue.

 

[Scott06]

They are not the quietest engine around. I think it is coming from the front but would also pull the drive to rule out drive gimbal etc. Also run it without the belt on to see if the water pump is bad.

Im thinking the noise may be valvetrain or timing gear related. Might look to see if there is play in timing gear by taking cap off and turning the crank by the balancer, see how much slack there is. I cant recall if one of the gears is fiber coated or not on these. Other item is to pull the valve cover to see if one of the rockers has slack. Could be an issue with cam lobe, pushrod, or rocket stud pulling out and creating lash in valvetrain.

can also do a cylinder drop test by pulling plug wires while running to see if the noise changes. I believe if you have a bad rod bearing it should change pitch when that plug is disconnected

 

[kenny nunez]

Do like Scott06 said about removing a spark plug wire when the noise is present, if there is any piston or rod noise and it goes away then it is time for a rebuild. The other thing that will make noise is the fuel pump if the tension spring is broken and the lever is slapping the cam lobe.

 

[Scott06]

The other thing that will make noise is the fuel pump if the tension spring is broken and the lever is slapping the cam lobe.

Good point about the fuel pump. That is probably the most likely.

 

[eriewalleye]

Welp life happens and I was not able to work on my boat for some time. I now again have some free time and wanted to post again here to explain what I have done and found. To start I am positive the noise is coming from the timing gear cover. The video I posted makes the noise seem excessively loud but in person it is much quieter and can not even be heard with the cover on. The noise is also only at idle and around 1500 to 2000 rpm is completely gone. So, here is a list of what I have done and sadly the noise is still there but is slightly reduced. The drive was pulled and it did not change the noise. While off I replaced the impeller which was a bit worn but not shot and all the gaskets and o rings. The drive was reinstalled. With the motor running I pulled the spark plug wires one by one and the noise did not change. Got zapped but I'm used to that in my line of work. I noticed a very small leak from one of the water hoses so all hoses were replaced. I also noticed the water temp never got up to operating temperature and found the thermostat was stuck open and the water temperature sensor was faulty. Both were replaced. Running the motor again I found the oil pressure gauge was bouncing like crazy so the oil pressure sensor was replaced only to find a small break in the wire which was cut out and corrected. The oil pressure is now around 20-25 psi at 2000 rpm and was confirmed with a mechanical gauge. lower than my original reading but seems to be in spec from what I have read. The old fuel was drained and fresh ethanol free gas was added. Oil (25w-40) and filter have also been changed again. this time I cut open the filter and found no metal in it or on the oil plug. The valve cover was removed and all the valves have been adjusted per the manual. Cover reinstalled with new gasket. During that process the lifter cover was removed and all lifters were inspected with no issues found. All parts back in their original position and new gasket installed on cover. New spark plugs were installed and the gaps set at .035". The mechanical fuel pump (filled with rust) was replaced and during this process I discovered that the clear inline fuel filter was not legal for a boat. So, all new marine grade fuel lies were installed along with a inline water separating fuel filter. At this point the noise was still there only at idle but I decided to take it out and put a load on the motor for a while. It runs great at any throttle however I only pushed the motor to a max of 3500 rpm. After an hour or so on the water at different speeds the noise is still taunting me. I know some of the things I did to the motor would not have any effect on the noise issues but they needed to be done. At this point I suspect the issue to be in the timing gears so I plan to support the motor remove the timing gear cover and have a look. After that if I have not found the issues I suppose I have no choice but to pull the motor or just run it and keep an eye on it. For those who replied to my first post thank you much for the advise. For anyone coming across this I now understand how frustrating chasing these noises can be. Safety first when on the water! If any one has any further advise or tip and tricks I'm happy to listen. I will come back and post again when I get further. Bring out another thousand they say. Man oh man.

 

[Scott06]

Welp life happens and I was not able to work on my boat for some time. I now again have some free time and wanted to post again here to explain what I have done and found. To start I am positive the noise is coming from the timing gear cover. The video I posted makes the noise seem excessively loud but in person it is much quieter and can not even be heard with the cover on. The noise is also only at idle and around 1500 to 2000 rpm is completely gone. So, here is a list of what I have done and sadly the noise is still there but is slightly reduced. The drive was pulled and it did not change the noise. While off I replaced the impeller which was a bit worn but not shot and all the gaskets and o rings. The drive was reinstalled. With the motor running I pulled the spark plug wires one by one and the noise did not change. Got zapped but I'm used to that in my line of work. I noticed a very small leak from one of the water hoses so all hoses were replaced. I also noticed the water temp never got up to operating temperature and found the thermostat was stuck open and the water temperature sensor was faulty. Both were replaced. Running the motor again I found the oil pressure gauge was bouncing like crazy so the oil pressure sensor was replaced only to find a small break in the wire which was cut out and corrected. The oil pressure is now around 20-25 psi at 2000 rpm and was confirmed with a mechanical gauge. lower than my original reading but seems to be in spec from what I have read. The old fuel was drained and fresh ethanol free gas was added. Oil (25w-40) and filter have also been changed again. this time I cut open the filter and found no metal in it or on the oil plug. The valve cover was removed and all the valves have been adjusted per the manual. Cover reinstalled with new gasket. During that process the lifter cover was removed and all lifters were inspected with no issues found. All parts back in their original position and new gasket installed on cover. New spark plugs were installed and the gaps set at .035". The mechanical fuel pump (filled with rust) was replaced and during this process I discovered that the clear inline fuel filter was not legal for a boat. So, all new marine grade fuel lies were installed along with a inline water separating fuel filter. At this point the noise was still there only at idle but I decided to take it out and put a load on the motor for a while. It runs great at any throttle however I only pushed the motor to a max of 3500 rpm. After an hour or so on the water at different speeds the noise is still taunting me. I know some of the things I did to the motor would not have any effect on the noise issues but they needed to be done. At this point I suspect the issue to be in the timing gears so I plan to support the motor remove the timing gear cover and have a look. After that if I have not found the issues I suppose I have no choice but to pull the motor or just run it and keep an eye on it. For those who replied to my first post thank you much for the advise. For anyone coming across this I now understand how frustrating chasing these noises can be. Safety first when on the water! If any one has any further advise or tip and tricks I'm happy to listen. I will come back and post again when I get further. Bring out another thousand they say. Man oh man.

You can probably diagnose the timing gears with out removing the cover. Take the plugs out turn the crank and see if there is excessive backlash making the cam, distributor shaft , or valve train move when you reverse crank direction. May have to pull lifter side cover to see cam

what oil pressure does it make when hot

 

[eriewalleye]

Thanks I will do that. I did forget to mention It was run with the belt off and the noise was still there. It was one of the first things I did to rule out the water pump.

 

[Bondo]

Ayuh,..... could be the fuel pump, which runs on a cam lobe,....

 

[eriewalleye]

Ayuh,..... could be the fuel pump, which runs on a cam lobe,....

Fuel pump was replaced along with the fuel lines. I cannot hear the noise with my stethoscope at the pump only the timing gears. Noises can travel though.

 

[eriewalleye]

You can probably diagnose the timing gears with out removing the cover. Take the plugs out turn the crank and see if there is excessive backlash making the cam, distributor shaft , or valve train move when you reverse crank direction. May have to pull lifter side cover to see cam

what oil pressure does it make when hot

Sorry didn't see to oil pressure question. When hot its about 22 psi at 2000 rpm 30 psi at 3000 rpm and 40 psi at 4000 rpm. I rarely ever run it at or over 4000 rpm.

 

[eriewalleye]

Welp life happens and I was not able to work on my boat for some time. I now again have some free time and wanted to post again here to explain what I have done and found. To start I am positive the noise is coming from the timing gear cover. The video I posted makes the noise seem excessively loud but in person it is much quieter and can not even be heard with the cover on. The noise is also only at idle and around 1500 to 2000 rpm is completely gone. So, here is a list of what I have done and sadly the noise is still there but is slightly reduced. The drive was pulled and it did not change the noise. While off I replaced the impeller which was a bit worn but not shot and all the gaskets and o rings. The drive was reinstalled. With the motor running I pulled the spark plug wires one by one and the noise did not change. Got zapped but I'm used to that in my line of work. I noticed a very small leak from one of the water hoses so all hoses were replaced. I also noticed the water temp never got up to operating temperature and found the thermostat was stuck open and the water temperature sensor was faulty. Both were replaced. Running the motor again I found the oil pressure gauge was bouncing like crazy so the oil pressure sensor was replaced only to find a small break in the wire which was cut out and corrected. The oil pressure is now around 20-25 psi at 2000 rpm and was confirmed with a mechanical gauge. lower than my original reading but seems to be in spec from what I have read. The old fuel was drained and fresh ethanol free gas was added. Oil (25w-40) and filter have also been changed again. this time I cut open the filter and found no metal in it or on the oil plug. The valve cover was removed and all the valves have been adjusted per the manual. Cover reinstalled with new gasket. During that process the lifter cover was removed and all lifters were inspected with no issues found. All parts back in their original position and new gasket installed on cover. New spark plugs were installed and the gaps set at .035". The mechanical fuel pump (filled with rust) was replaced and during this process I discovered that the clear inline fuel filter was not legal for a boat. So, all new marine grade fuel lies were installed along with a inline water separating fuel filter. At this point the noise was still there only at idle but I decided to take it out and put a load on the motor for a while. It runs great at any throttle however I only pushed the motor to a max of 3500 rpm. After an hour or so on the water at different speeds the noise is still taunting me. I know some of the things I did to the motor would not have any effect on the noise issues but they needed to be done. At this point I suspect the issue to be in the timing gears so I plan to support the motor remove the timing gear cover and have a look. After that if I have not found the issues I suppose I have no choice but to pull the motor or just run it and keep an eye on it. For those who replied to my first post thank you much for the advise. For anyone coming across this I now understand how frustrating chasing these noises can be. Safety first when on the water! If any one has any further advise or tip and tricks I'm happy to listen. I will come back and post again when I get further. Bring out another thousand they say. Man oh man.

I forgot to mention all cylinders were pressures tested all were between 130-135 psi.

 

[Scott06]

Sorry didn't see to oil pressure question. When hot its about 22 psi at 2000 rpm 30 psi at 3000 rpm and 40 psi at 4000 rpm. I rarely ever run it at or over 4000 rpm.

I edited the post and added it , I think your first response was while I was editing…

10 psi per 1000 rpm hot is fine. Check for backlash in timing . If I recall 3.0 s can be a little clacky or at least mine was. I think on the trailer and running on muffs it was louder than my current 5.0

 

[kenny nunez]

Earlier inline engines had fiber camshaft gears. Later they went to aluminum which is noisier than the fiber ones. I cannot 100% say that yours is either so the only way would be to pull the cover. Cut off the remaining pan gasket flush with the block and remove the cover to pan gasket. Pulling the cam is pretty routine with the lifters, fuel pump and distributor out.
Permatex or any similar sealer will re seal the gaskets that you removed.

 

[Grub54891]

Yes. Mine had the fiber gear, about 1/3 of the teeth were damaged enough to warrant replacing them. I went with metal gears. Really not that loud but I insulated the doghouse pretty well.

 

[eriewalleye]

Thanks for the tips guys. When I get there I will let you know what I find.

 

[eriewalleye]

I know it has been some time but I wanted to honor my word and report back when I got the motor fixed. Without further ado, it was my lifters. This process has been such a learning curve for me. I would like to thank all those who replied and helped to kept me motivated in resolving this issue. In a previous post I said the lifters were inspected and seemed to be okay but I looker right over the problem. I used a non OEM image of the lifters to reference the ones I pulled from my motor. It wasn't until later I saw a picture of the OEM lifters which made me wonder. There are two rings in the middle of the lifters that are machined in and were almost completely worn off of the ones I pulled from my motor. This is what tricked me as the picture I first used did not have these rings. After a little parts research I was able to find a kit made by Elgin which is an exact match to the OEM. Here is a link if anyone cares to see. https://www.amazon.com/dp/B08LMG8236?ref=ppx_yo2ov_dt_b_fed_asin_title
Being made mostly in the USA and Canada I felt good about using the parts. With a good soak in the 25w-40 all parts were installed, valves adjusted and engine is running great. As to why the lifters were worn out I suppose its hard to say. Could be age, running the motor on the wrong oil or gas by previous owner or even running it hard. No metal has been found in the motor so I am happy at this point. In the beginning of this forum I posted a video of the noise so here I will also attach a video of how it sounds now. Excuse me sounding like I'm 14 years old again I was just very happy to not hear the noise. Thanks again everyone. Happy boating and fishing to all!!!