Strange Engine Noise on 96' Merc 4.3V6 - Ideas?

[Boatman]

I lost out on boating last weekend, so although I know this will difficult to describe, have to ask for ideas.

My 96' Sweet 16 has a Merc 4.3V6 in it with less than, get this, 10 hours on it. Previous owner bought it in 97' and never used it. I bought it this spring and it is in immaculate condition. :) I have followed the break in procedure in the owners manual very closely.

I noticed a strange "rattle noise" coming from the top rear of the engine at idle speed. eek! Being in over my head at that point, took it in to the local, reputable dealer.

They eliminated the outdrive, as well as the belt driven pumps, etc as a source of the noise, leaving the engine itself.

Given the location, they suspect it is likely the rear bearing on the counterbalance shaft. Any other ideas from those more knowledgeable than I? :confused:

Thanks for any suggestions and for all the great reading on this site for a new Donzi owner such as myself.

[KMLFAMILY]

Just an idea.Can you change the noise by taking it in and out of forward or reverse.Thinking,possibility of cracked flywheel.You see it in vehicles. I don"t know if it could occur on a boat engine.

[Digger]

can you isolate whether the rattle is coming from the engine or your exhaust, just where it comes off the elbows? In a previous boat I had a "rattle" back there that ended up coming from the internal flapper in the exhaust (may not be the correct term), because the rubber lining around the flapper had worn away. Although it doesn't seem as though your boat would have enough hours on it to do that.... just a wild guess-
good luck-

[Boatman]

Thanks for the ideas. I'll check them out.

[MOP]

Another much less scary idea!! There are exhaust flappers in the Y pipe they have an irregular clacking sound that on some boats sound real bad. If you raise the idle to about 10-11--rmp does it go away? If so go out and have a good time, I had a mechanic friend of mine condemn a 502 EFI, pulled it out found nothing called Merc said tech almost fell off the chair laughing!

[MR MAGOO]

I`d guess that it is the exhaust flappers also

[Tidbart]

Ditto on the exhaust. I had a day or two wondering what that noise was.
B

[Boatman]

Thanks for all the replys - I'll ask that they check the flappers before pulling the engine apart! I'll re-post with the outcome!

[TRU-JACK]

Hey Boatman where do you boat? I have a similar setup and am interested in tuning the engine a bit. Have you done anything to yours? wink

[Boatman]

To All: Well, I spoke to the mechanic today (who incidentally things I'm nuts as I call him at least once a day). Anyway, he was well familiar with the exhaust flapper phenomenom and assured me that wasn't the problem or I would have been on the water last weekend with his encouragement.

TRU-JACK: We have a family cottage just south of Parry Sound on a smaller pair of lakes called Blackstone & Crane Lake. I am close to Lake Joseph, so that is where I get my "big" water. Haven't done any tuning, but I'm open to the idea! Do you know any other Donzi owners or local clubs, etc. for local fun? I'd be interested in connecting with other boating and have a good roller trailer so can get around.

[CrackerJack]

I have the same set up you do on my 16'. Did you figure out where the noise was coming from? If not does it sound like an engine knocking noise? We have a noise coming from the engine compartment, but when you open the hatch up at idle speed, it's not heard. Me and my son came to the conclusion it's an echo with the thru-hull exhaust.(No flappers)

Maybe this could be of some help?

[Rootsy]

NOISES SUCK! for 2 days i thought i had a high speed miss of a serious nature... thought i lost a cylinder or wiped a camshaft lobe... the exhaust just went flat sounding with all the wind whippin past your head

AND... in the end it turned out to be the damn hatch vibrating... :rolleyes:

yep i'm an idiot...

[Boatman]

Thanks for all the ideas and the sympathy :rolleyes: - I'm bummed about it for sure as the long weekend in Canada is this coming weekend and I'm certain it won't be resolved by then. I'm definitely a boat freak as I can't think of anything else.

Anyway, I'll post the outcome when it's known in case it helps someone in the future.

All the best and thanks! :D

[Formula Jr]

"yep i'm an idiot..."

No you're not, that happens to everyone with time.
I was on the same tract for a week till I traced it to a hatch. They can make sounds just like bad engine sounds. :D

[CnV & Family]

We had a non-constant buzz/rattling noise on our 97' w/same setup... After about 4 outings and lots of concern and pondering... turned out to be the hatch. To fix, I took a section of .5in rubber tubing, cut it into four 1.5in sections, and cut a slit in those sections. After that I just placed them evenly on the edges of the hatch. Makes it nice and snug w/no vibration, even in the rougher stuff.

-C

[Rootsy]

now that is a good idea CB&V...

jr... sarcasm sir.. sarcasm, but thanks for the vote of confidence wink

now did i ever tell ya bout the rack of sockets i misplaced as a teenager??? just think well lubricated... eek!

[CnV & Family]

Ohhhh yeah... and it keeps the wearing on the colors/stripe in the front of the hatch to a minimum/almost nonexistant state...

[TRU-JACK]

Boatman, there is a board member named Danny who has a 16 and maybe a hornet, i'm not sure. He's in midland and seems to be quite knowledgable and a nice guy. His boats look great, and i considered the 16 he now has, but it needed some tlc and he certainly did a nice job. We should keep in mind and maybe see what type of response we get from fellow Donzi owners, but it would be a great day or weekend to run throught the muskoka's with a pack of Donzi's. Any ideas or anyone interested? Let's get the ball rolling. wink

[Boatman]

Well gang, here's the final word on the "strange" engine noise. Had the engine pulled and they found a "spun bearing" on the #6 Connecting Rod and the Crankshaft. Everything else was fine.

The mechanic was as puzzled as me, and guessed that it may have been dry upon start up after sitting idle for so many years.

The End (Except for the Bill!)

[Boatman]

The problem that I started this thread about was ultimately traced back (after 2 successive main bearing failures) to an incorrectly plumbed remote oil filter kit.

Mercruiser ultimately has honored a warranty claim outside of the period of eligibility because their assembly instructions provided with the kit were incorrect (and followed diligently by whomever installed the kit originally).

My credit to my local Donzi Dealer (Gordon Bay Marine in Canada) and to Mercruiser for ultimately "doing the right thing".

Happy Boating!!!

[CrackerJack]

Go do some Donzing now!!!!!
Good luck, Jack

[Andy knuth]

Hey guys i'd be interrested in a northern donzi get together.I;v got a 67 18' that trailerd regularly.Ilive in Georgtown and family cottage in port severn.As soon as the snow melts and I can my motor in I'm ready to go.