1986 4.3L Mercruiser V6 Knocking noise?

[Silvertip]

That knock sounds awful "tinny" like it might be a loose pulley on the front of the motor.

 

[Chadbud]

That knock sounds awful "tinny" like it might be a loose pulley on the front of the motor.

Okay guys I pulled the shaft pin and lowered the outdrive all the way down. Crossed my fingers and prayed to god and tried to start her. She fired up and the knock is still there. Now, like silvertip said.. the sound is very "tin" sounding.. it also sounds like it's coming from right in front of the motor where the pulleys are. How do I check if it's one of the pulleys? I did put the belts on myself so maybe I messed up somewhere. What do you guys think I should do now? Gotta hurry too because it will be getting below 35 in my area within the next week! Gotta drain her water soon. Thanks!

Thanks!

 

[shaw520]

power steering pump ??,.. if you take a wooden dowel and lay it on various components while its running to get a better "feel" for where its coming from

 

[Scott06]

Take all the belts off you can run it briefly with no accessories. Noise gone it's the ps, water pump, or alternator

 

[Chadbud]

Okay guys first I'd like to thank everyone for taking the time to help me and read my responses.

Alright so, I just winterized the engine by draining it and then pouring antifreeze down the water cooling tubes near the thermostat. I did this because some nights where I live it's starting to drop down to the 30s.

My next move is to remove the belts and start her up.. hoping that I will not hear the knock. If the knock persists after I do that, then what is my next step? Could it be the pulleys like one user said? I'm trying to rule out everything before I decide that it is a rod/bearing issue. Please take a second listen to the video I posted and let me know any ideas you have.

I appreciate the support and feedback so much. Please if anyone has any input, feel free to give me your 2 cents.

Thanks!

 

[No Worries]

Have you pulled the valve covers and inspected the valve train? Just make sure there's no rockers bouncing around in there. Also, consider pulling the lower unit right off (you should store it anyhow) and see if the shaft and joints look okay. Maybe someone can chime in on cranking the motor over this way with the coil wire removed. As in, would it harm the motor? Maybe just for a couple seconds to see if the noise is gone with the lower unit removed.

 

[harleyman1975]

You can run engine for a minute at idle speed with belts off and lower unit removed and not hurt anything...longer than that and exhaust shutters would be in danger of burning up.

 

[G_Hipster]

It's pretty loud. Pulling the belt and spinning the components by hand might reveal something. Loose water pump impeller maybe but I'm thinking deeper then that. Like a broke or loose rod cap and it has a ring to it like the cranks getting hammered . The trim pump, you can try disassembling the motor and clean up the brushes and commutator with some fine emery cloth. My new to me boat's was "stuck" from sitting.

 

[Chadbud]

UPDATE: Okay guys I pulled the belts yesterday and gave it a try.. much to my heartache, the knocking persists. I tried listening as closely as I could and it seems like it's coming from the front right side of the engine.. if you're looking back at it from the front of the boat.

What do you guys think? Is there anything else I haven't checked that it could be? I appreciate anyone who's been keeping up with my issue here, I can't tell you how much it means to me.

 

[G_Hipster]

The only other thing I can think of is a loose flywheel will make a helluva racket, and if not it's time to pull the pan.

 

[harleyman1975]

I think it is time to pull her out and pull the pan...

 

[Bondo]

What do you guys think? Is there anything else I haven't checked that it could be?

Ayuh,..... A compression test is a pretty good indicator of the motor's internal health,....

A bad rod bearin' can sometimes be isolated by pullin' off the plug wire to that cylinder, it'll go quiet,....
or atleast noticeably quieter,...

I'd pull the drive off, 'n try 1 last time,.....
If quiet, it's the drive,....
If not, it's probably time to pull the motor, 'n find the problem on a stand, insteada in the hull,....

To pull the drive, shift into forward, remove the 6 nuts, 'n Pull,....
It's gotta come off, before the motor comes out, anyways,....

 

[leftcoast]

I've had a similar problem several years ago. It turned out to be a stuck valve plus other problems from water getting into engine.
I would either pull the valve covers and check for a loose lifter (suggestion from earlier post) or check compression. If you check compression it will be pretty much zero.

If this is the problem, the noise is from the piston hitting the stuck valve. If your lucky you may be able to just pull the head and have it rebuilt.

I lost (2) 4.3 engines from this same problem. Now I always run the engine for about 30 seconds at idle after flushing. No problems for the last 15 yrs. and water pump impeller still looked new after 4 years.

Good luck,
Jim

 

[Silvertip]

Grounding means the metal shell of the motor must be connected to ground (the negative battery terminal) . It achieves grounding because it is bolted to metal housings that ultimately are bolted to the engine block which is where the negative battery cable is connected. Use a jumper cable fastened to the motor housing and the other end to the negative battery cable. Then repeat the positive red wire to the motor leads as you did before. Nothing happens the next step is to look for a new motor. Or just remove the motor, disassemble it, and see if there is a problem. Bench test it using any 12 volt battery.