88' Mercruiser 165 harmonic sound

[Cal-b]

First off, thank you to everyone on this forum. I have been an outsider looking in and have learned a lot through your discussions. I bought a 1988 Lund Tyee 5.5 last year with an MCM 165 and alpha 1 stern drive. The boat had only 86 original hours on it, garage kept its whole life. I addressed some preventative maintenance stuff such as impeller replacement, exhaust riser gasket, stern drive lube and alignment, carb rebuild, etc. The engine has been running great for 40 hours, but has developed a harmonic type noise that seems to be resonating through the oil pan. I have recorded a video of the sound but am having issues with upload. Compression test today shows the following
Cylinder 1 - 130
Cylinder 2 - 130
Cylinder 3 - 123
Cylinder 4 - 138
Oil pressure at idle is higher than normal - around 70 psi. The oil pressure drops a few psi with the harmonic sound. Could this be an issue with the oil pump?

 

[Bt Doctur]

Ill take a guess and say a cracked flywheel dust cover if its a metallic clanking . Had the same thing happen on mine a long time ago

 

[Scott Danforth]

those compression numbers are low, hopefully its your gauge

does your motor still use the original stator under the harmonic balancer for charging, or was it converted to an alternator? could be a magnet coming loose or the dust cover, or the exhaust flappers have burned up from lack of cooling water flow.

videos can only be loaded on sites like youtube and the link posted.

currently we have server issues preventing the uploading of pictures.

 

[Cal-b]

The engine is all original. The sound/vibration is enough to feel when I put my hand on the engine.
I've uploaded the video to Youtube, please see link below.

 

[Dubed]

Sounds like it coming from the back of the motor. I would pull the drive and run it, see if the noise goes away

 

[Cal-b]

I did this the other day, but with the sound of the exhaust being out of the water it was hard to tell. I checked the gimbal bearing, splines, and u-joints. Bellows and internals are completely dry, no signs of water intrusion. I will pull the drive in about an hour and fire it up again.

 

[Scott06]

if it has a greaseable gimbal bearing grease it and see if noise changes. I would also lean towards gimbal bearing Ujoint or drive noise

 

[Scott06]

I did this the other day, but with the sound of the exhaust being out of the water it was hard to tell. I checked the gimbal bearing, splines, and u-joints. Bellows and internals are completely dry, no signs of water intrusion. I will pull the drive in about an hour and fire it up again.

we posted at same time.. if you already did that maybe try taking the belt off the front and see if noise goes away

 

[Cal-b]

No belt on this engine, it still has the original charging system. My cousin is thinking that it could potentially be a blockage/issue causing oil to flow through a pressure relief valve in the oil pump. The noise seems to be resonating in the oil pan, the oil pressure is high, and the oil pressure slightly drops when the sound is loudest. The way the pump and tube are mounted I could see how a vibration could be amplified into a harmonic resonance. I have swapped filters but no change in sound.

 

[Scott Danforth]

Its not the oil pump.

pull the drive and run it. my guess the sound goes away.

 

[Scott06]

Its not the oil pump.

pull the drive and run it. my guess the sound goes away.

he already did see post 6

 

[Scott06]

No belt on this engine, it still has the original charging system. My cousin is thinking that it could potentially be a blockage/issue causing oil to flow through a pressure relief valve in the oil pump. The noise seems to be resonating in the oil pan, the oil pressure is high, and the oil pressure slightly drops when the sound is loudest. The way the pump and tube are mounted I could see how a vibration could be amplified into a harmonic resonance. I have swapped filters but no change in sound.

I was thinking straight 6 165 not the 4 thanks.

is oil pump driven off distributor ?

 

[Cal-b]

I just pulled the drive off again, fired it up and the sound is still there. Had to get my head down near the oil pan to hear over the exhaust, but it's definitely still there.

 

[Cal-b]

I was thinking straight 6 165 not the 4 thanks.

is oil pump driven off distributor ?

I'm not familiar with how this pump operates. I've been unable to find a service manual and have not had this engine apart.

 

[Scott06]

I'm not familiar with how this pump operates. I've been unable to find a service manual and have not had this engine apart.

here is a link to all the various parts diagrams that engine (there is a search by serial number that would be more accurate)

https://www.marineengine.com/parts/mercruiser-sterndrive-parts/165-2-bbl-mercury-224-il4-1987/0b434941-thru-0b774251

 

[Scott Danforth]

pump is driven off dizzy at front of the motor. pump drive is a hex.

dizzy is same small body casting as the old chev vegas

here are some pics pulled from this hotrod thread. https://www.jalopyjournal.com/forum/threads/the-elusive-224-3-7-mercruiser-banger.256713

 

[Dubed]

Perhaps pull the dizzy and turn the pump with a drill and long hex rod, see if it duplicates the noise. I used that method to prime my rebuilt 3.7 before firing up

 

[cyclops222]

It sounds just like a fan / air pump. Does engine have a E G R Valve ? Remove the EGR and plug closed both open ends of the tubes.

 

[tank1949]

First off, thank you to everyone on this forum. I have been an outsider looking in and have learned a lot through your discussions. I bought a 1988 Lund Tyee 5.5 last year with an MCM 165 and alpha 1 stern drive. The boat had only 86 original hours on it, garage kept its whole life. I addressed some preventative maintenance stuff such as impeller replacement, exhaust riser gasket, stern drive lube and alignment, carb rebuild, etc. The engine has been running great for 40 hours, but has developed a harmonic type noise that seems to be resonating through the oil pan. I have recorded a video of the sound but am having issues with upload. Compression test today shows the following
Cylinder 1 - 130
Cylinder 2 - 130
Cylinder 3 - 123
Cylinder 4 - 138
Oil pressure at idle is higher than normal - around 70 psi. The oil pressure drops a few psi with the harmonic sound. Could this be an issue with the oil pump?

Buy cheap stethoscope from Harbor Freight. I suspect alternator.

 

[nola mike]

It sounds just like a fan / air pump. Does engine have a E G R Valve ? Remove the EGR and plug closed both open ends of the tubes.

No egr