1981 Mercruiser 120 knocking

[Mike Lukacevic]

The boat is new to me. It has 422 hrs on it. I’ve done a valve adjustment on it. Dynamic then cold. The engine oil looks like new. It this knock. Hard to tell wear it’s coming from but maybe top and front. Appears that way. I removed the belt to see if the accessories were involved. Doesn’t appear to be. Hers a video. Kinda nervous about this but it runs smooth.

 

[Mike Lukacevic]

Here is the video. Not sure what happened

 

[Bondo]

Ayuh,..... Welcome Aboard,..... Have ya tried the ole broom stick to localize the knock,..??

 

[Mike Lukacevic]

Ayuh,..... Welcome Aboard,..... Have ya tried the ole broom stick to localize the knock,..??

I’ve got a stethoscope and plan to zero in on it TMMRW. I see my attachment never came through.

 

[nola mike]

I’ve got a stethoscope and plan to zero in on it TMMRW. I see my attachment never came through.

You might need a certain number of posts to add it, try a YouTube link

 

[Mike Lukacevic]

Here is the sound my good running engine makes. I hope this youtube link works. I’m trying my best.

Any ideas ? The engine has 422 hours on it. Not run a lot. A 1981

 

[Mike Lukacevic]

Here’s another view of the engine running.
Did a valve adjustments both static and dynamic. I’m assuming the timing is fine but the timing plate is either rusted off or torn off, but since I’ve gotten pure 12v to the coil it jumps to life.
I’m new to this engine but not new to motors. However this noise ain’t right. I’ll bring out the stethoscope tomorrow and keep everyone updated. I know yer at the edges of your seats.
I’ve also restored MGB engines so I kinda get these old 4 cylinders.

 

[Mike Lukacevic]

You might need a certain number of posts to add it, try a YouTube link

I’m pretty sure I got it , my brother

 

[Mike Lukacevic]

You might need a certain number of posts to add it, try a YouTube link

Done. Youtube link works great

 

[Bondo]

Here is the sound my good running engine makes. I hope this youtube link works. I’m trying my best.

Any ideas ? The engine has 422 hours on it. Not run a lot. A 1981

Ayuh,..... This one sounds like a rod knock, or wrist pin / piston slap,....

Did you pull each plug wire to see if any caused a change,..??

 

[Mike Lukacevic]

Ayuh,..... This one sounds like a rod knock, or wrist pin / piston slap,....

Did you pull each plug wire to see if any caused a change,..??

Oh no. Catastrophic. The one Iron Duke with low hours that craps out. Swell. All prepared to do that and I can’t get power to the starter or the solenoid is bad. Jebus. It started out so promising. Thanks….I guess

 

[Bondo]

Oh no. Catastrophic. The one Iron Duke with low hours that craps out. Swell. All prepared to do that and I can’t get power to the starter or the solenoid is bad. Jebus. It started out so promising. Thanks….I guess

Ayuh,...... It ain't an Iron Duke,..... which is a Pontiac based 2.5l used by GM it the years after the '60s, a 151 cid motor,.....

What you've got is a Chevy, 153 cid motor based on the ole '60s I-6,...... with 2 less cylinders,....
The 3.0l boat motors are the same, bored, 'n stroked 153s,....

'n You've gotta do yer own diagnostics,..... I can't do it from a video,...

 

[Mike Lukacevic]

Ayuh,...... It ain't an Iron Duke,..... which is a Pontiac based 2.5l used by GM it the years after the '60s, a 151 cid motor,.....

What you've got is a Chevy, 153 cid motor based on the ole '60s I-6,...... with 2 less cylinders,....
The 3.0l boat motors are the same, bored, 'n stroked 153s,....

'n You've gotta do yer own diagnostics,..... I can't do it from a video,...

I’m spending all days off diagnosing. Just as I get one thing worked out, I can’t get ignition working. Was getting really weird stuff happening. Then replaced the switch. Seems. Okay. I gotta get it started again and pull out the stethoscope

 

[Mike Lukacevic]

Now that I’ve got all wiring and ignition bits worked out, this thing fires like a champ. Bypassed the resistor wire with this electronic ignition. Fires almost as fast as my 79 MGB.
It’s still knocking. Towards the front I think. Took my stethoscope out and went over the entire thing. Got too close to the alternator fan with my forearm a gave myself areal bad battle wound.
It’s hard to discern even with the stethoscope where exactly it is. Seems around the dizzy area. But not specific. That side I’m sure. Timing gears. Dizzy. Fuel pump.
Removed wires one by one and there was zero change. Did this numerous times. I swear it sounds like a diesel running. It pretty much goes away at 1800-2000 then sounds just like a motor.
I haven’t put a timing light on it cuz there’s no clear misfire. I think this thing will run on one cylinder. Certainly runs on two. I was getting zapped with work gloves on so wires are on their way. Arcing all over the place when disconnected.

 

[Mike Lukacevic]

Also was gonna take the oil filter off and tear it apart to look for shavings. No filters locally.
The oil is the color of honey. The seller probably dumped 5 quarts of ALDI oil into it before I bought it. Liqui Moly arriving soon. Hope it does something. Wanna get outta the driveway.