3.0L driveline knocking noise...HELP!

[chargedstang89]

Re: 3.0L driveline knocking noise...HELP! *update*

Re: 3.0L driveline knocking noise...HELP! *update*

Ok, we took the boat out tonight and the same noise is still there. Putting my ear to the valve cover, it's not coming from the motor. It's coming from the rear of the engine area, and sounds like it is coming from down low, by where the output shaft from the rear of the motor is spinning.

Could this be that exhaust flapper part, causing the noise? It sounds like a cross between some type of a metal knock and an exhaust leak.

 

[chargedstang89]

Re: 3.0L driveline knocking noise...HELP!

bump...please see question above...

 

[Haut Medoc]

Re: 3.0L driveline knocking noise...HELP!

Have you looked to see if your exhaust shutter is still in place?...​

 

[chargedstang89]

Re: 3.0L driveline knocking noise...HELP!

No, I haven't. Where is this located and what does it look like?

 

[Haut Medoc]

Re: 3.0L driveline knocking noise...HELP!

It is locted in the exhaust pipe just below the exhaust riser, which you will need to remove to inspect......
It looks like a 'flapper'......
They will rattle, but you said your noise is further down....
If it came loose & lodged itself down at the bottom, I would think that you would notice the restriction under load......
Worth checking, there really are not alot of moving parts down there....​

 

[chargedstang89]

Re: 3.0L driveline knocking noise...HELP!

at the risk of sounding dumb, where is the exhaust riser? Do I have to take the lower unit off or anything? I'm excellent with cars, just new to the whole boat mechanic thing. I have the clymer's manual for it, but not here at work with me.

 

[Haut Medoc]

Re: 3.0L driveline knocking noise...HELP!

No you do not need to remove the drive.....
It is the 'elbow looking thing that is attached to the exhaust manifold on one end & a 3-4" rubber 'boot' on the other end.....
The shutter is directly below that 'boot'......​

 

[chargedstang89]

Re: 3.0L driveline knocking noise...HELP!

Okay, I took the exhaust riser off, and removed the flapper valve for inspection. The rubber is worn off a little on the edge, and there's shiny metal markings on the inside of the lower elbow, that shows the metal on the flapper valve has been hitting the elbow. We're going to get a new flapper, but the noise I hear sounds WAY louder then this little part should be sounding.

By coincidence, my dad told me to check the tigtness of the exhaust manifold bolts because the rear 2 bolts had previously sheared off for whatever reason. Wouldn't you know it, I just grab the rear stud and it pulls right out. It's broken off up in the block.

I removed the exhaust manifold. all other studs were okay. Tried drilling a pilot hole in the bolt, and using an EZ-out, but the shank of the ez-out broke. So, today, we're going to use a left handed drill bit to drill it and grab it and hopefully break it loose, then put everything back together.

It's just a guess, but my guess is that this would more then likely be the cause of the noise I'm hearing. If not, then I give up!

 

[chargedstang89]

Re: 3.0L driveline knocking noise...HELP! *update #2*

Re: 3.0L driveline knocking noise...HELP! *update #2*

Well, we went and bought some grade 8 bolts to replace the last broken stud that holds the exhaust manifold on. I had to use an easy out to get the old broken stud out, but she came loose. Got everything put back together and fired it up with muffs in the driveway. At a fast idle, everything sounded good, but then I climbed into the boat and noticed that water was spraying out of the exhaust riser.

Shut it down and pulled the riser back off. There was a bunch of old gasket material baked onto the riser that I didn't see. Used a scraper and a boar's hair wheel on my air grinder to remove and smooth the surface. Put a little ultra blue RTV and the gasket back on. CAREFUL to not cover the water ports, so there is no worry there.

I will be testing it tomorrow morning on the river, so I'll post back up, but hopefully the broken exhaust stud, and the flapper valve were the problems! ****Crossing my fingers and knocking on wood****

 

[jmanjeeper]

Re: 3.0L driveline knocking noise...HELP!

I have the same noise on my 92' 4.3l Merc. Please post your results so I can attempt to fix mine a little easier! Thanks!

 

[mcdonald331]

6cyl mercruser lower end won't move

6cyl mercruser lower end won't move

sorry for butting in but i can't seem to get into any other forum. please if someone could answer this question i would be fore ever in your debt.
i have a 1980 6cyl mercruser inboard which i just got and i don't know much about an inboard but it starts and runs good except the prop won't spin (i filled the lower end with lube) and the trim won't move what could be wrong

 

[chargedstang89]

Re: 3.0L driveline knocking noise...HELP!**final update**

Re: 3.0L driveline knocking noise...HELP!**final update**

PROBLEM S-O-L-V-E-D!!!!

It looks like the new exhaust manifold bolts and flapper valve fixed the problem. As mentioned before, I found that the rear stud that holds the exhaust manifold to the block was broken. The flapper valve had rubber worn off of the edges and was rubbing the inside of the lower exhaust pipe.

Pulled the manifold, put a new gasket on, and replaced the rear stud with a GRADE 8 bolt, and put the new flapper valve in. torqued everything down, and tested it yesterday. The boat now purrs like a kitten, so it looks like after all that work, it was just a possible exhaust leak with maybe a little tapping from the flapper valve.

I hear valve noise too, so I'll be adjusting the valves within the next couple of weeks, but that ridiculous noise is now gone!! Thanks to everyone for their help!!!

 

[jmanjeeper]

Re: 3.0L driveline knocking noise...HELP!

glad to hear it! now i just need to find the time to work on mine, lol...I looked down the back of my motor and saw 2 bolts, one was backed out a bit, I tried to tighten it back down but it seems stripped....anyone?

 

[wgcoyote]

Re: 3.0L driveline knocking noise...HELP! *update*

Re: 3.0L driveline knocking noise...HELP! *update*

Ok, we took the boat out tonight and the same noise is still there. Putting my ear to the valve cover, it's not coming from the motor. It's coming from the rear of the engine area, and sounds like it is coming from down low, by where the output shaft from the rear of the motor is spinning.

Could this be that exhaust flapper part, causing the noise? It sounds like a cross between some type of a metal knock and an exhaust leak.

look at the top cap 4 bolt ther is a bearing on top i had it happen to me i trash my upper uint

 

[chargedstang89]

Re: 3.0L driveline knocking noise...HELP! *update*

Re: 3.0L driveline knocking noise...HELP! *update*

look at the top cap 4 bolt ther is a bearing on top i had it happen to me i trash my upper uint

See above...I was able to fix the problem. Ended up being an exhaust leak from a broken stud in the exhaust manifold and possibly some tapping from the flapper valve as well. Thanks, though!

 

[Dante04SRT]

Re: 3.0L driveline knocking noise...HELP!**final update**

Re: 3.0L driveline knocking noise...HELP!**final update**

PROBLEM S-O-L-V-E-D!!!!

It looks like the new exhaust manifold bolts and flapper valve fixed the problem. As mentioned before, I found that the rear stud that holds the exhaust manifold to the block was broken. The flapper valve had rubber worn off of the edges and was rubbing the inside of the lower exhaust pipe.

Pulled the manifold, put a new gasket on, and replaced the rear stud with a GRADE 8 bolt, and put the new flapper valve in. torqued everything down, and tested it yesterday. The boat now purrs like a kitten, so it looks like after all that work, it was just a possible exhaust leak with maybe a little tapping from the flapper valve.

I hear valve noise too, so I'll be adjusting the valves within the next couple of weeks, but that ridiculous noise is now gone!! Thanks to everyone for their help!!!

Got any pics of the process/parts? I have the same motor and very similar sounding problem.

 

[Don S]

Re: 3.0L driveline knocking noise...HELP!**final update**

Re: 3.0L driveline knocking noise...HELP!**final update**

You don't need pic of how he fixed his problem, you need to find out what your problem is and fix it.
An OEM service manual will give you all the step and pics you need.......... No a Clymers or Seloc will not work.