rapping

[bjf1280]

My 350 Mercruiser has a rapping noise at all speeds and also in nuetral and reverse. Ran great for a half hour while tubing then heated up. thought intake was glogged so I stopped, put it in reverse to blow the intake clear and it cooled right off. Same thing happend a half hour later, repeated steps and was off tubing again untill the rapping started. Now it sits on the mooring waiting for some help. Oh buy the way, the water pump has about 5 hours on it as well as new manifolds.

 

[Bondo]

Re: rapping

You'll have to narrow the search for the Knocking,........

Is it the Motor,..??...... Is it Up High in the Motor,+ or Down low,..??.....

Is it the Motor,....??.... Or the Drive,..??....

 

[69slickcraft]

Re: rapping

would the rapping be water boiling in the block from a bad thermostat?

 

[bjf1280]

Re: rapping

It sounds to me like it's comming from the top of the engine not the drive. And the thermostat is new.

 

[bjf1280]

Re: rapping

You'll have to narrow the search for the Knocking,........

Is it the Motor,..??...... Is it Up High in the Motor,+ or Down low,..??.....

Is it the Motor,....??.... Or the Drive,..??....

 

[searay3]

Re: rapping

Sounds can travel thru the driveline/engine. Take a close look at the motor along where the belts run. If you see any rubber piling up and unusual wear on the belts. Could be loose and rubbing on something under load. Looks good? Remove the drive and feed water to the fitting that goes from the impellor/drive thru the transom and start it. If the noise went away, it's in the drive. You will be able to see the ujoints/input shaft/gimble/coupler. Look good? Have to use a stethoscope to narrow down what part of the engine is suspect. Once you get an idea of where the noise is coming from, post back and go from there....

 

[bjf1280]

Re: rapping

Thanks, I was hoping it was something I could do in the water but I guess I'll have to pull it. I'll let you know how I make out.

 

[Blk-n-Blu]

Re: rapping

Engine circulating pump???8)

 

[bjf1280]

Re: rapping

Engine circulating pump???8)

 

[bjf1280]

Re: rapping

If thats the case where is the noise coming from?

 

[Don S]

Re: rapping

Sounds to me like you are looking for an "EZ Button" to push to fix your problem. Hate to say this, but it ain't gonna happen.
Nobody here can hear the noise you hear, all we get to see is your typing skills.
People can make suggestions, and as you have seen there is always a list of opinions. So what do you do? You start checking things. If you don't have a service manual, you are unarmed for battle.

 

[Limited-Time]

Re: rapping

You have a blown head gasket between two cylinders. My guess is 5 and 7, it happened when the engine over heated..........................Well thats my guess anyway. As Don S stated it's time for some trouble shooting. I'd start with a compression test.

 

[bjf1280]

Re: rapping

Sounds to me like you are looking for an "EZ Button" to push to fix your problem. Hate to say this, but it ain't gonna happen.
Nobody here can hear the noise you hear, all we get to see is your typing skills.
People can make suggestions, and as you have seen there is always a list of opinions. So what do you do? You start checking things. If you don't have a service manual, you are unarmed for battle.

 

[bjf1280]

Re: rapping

As a boat owner I have come to learn there is no EZ button, I'm just looking to see if this has happend to anyone else and maybe repair it myself if possible. These web sights have been very helpful in the past so thought I'd give it a try before hauling the boat and bringing it to my mechanic. Thanks for the help, I now have few ideas as to what it might be.

 

[Limited-Time]

Re: rapping

As a boat owner I have come to learn there is no EZ button, I'm just looking to see if this has happend to anyone else and maybe repair it myself if possible. These web sights have been very helpful in the past so thought I'd give it a try before hauling the boat and bringing it to my mechanic. Thanks for the help, I now have few ideas as to what it might be.

FWIW my response was prompted by personal experience........school of hard knocks. I hope your problem does not turn out as costly as mine.

 

[whywhyzed]

Re: rapping

Every tech has heard many a "rapping" engine... could be one of 100,000 possible causes.
If I hear a rapping in an engine.... and it's the exact same rapping I heard in another engine last week, same model.....doesn't matter....I make no connection to last week's repair, I begin to diagnose step by step. Step 1- fluid check and compression test.

 

[Reel Poor]

Re: rapping

One of these helps me isolate noises.

Mechanics Stethoscope

 

[bjf1280]

Re: rapping

One of these helps me isolate noises.

Mechanics Stethoscope

 

[bjf1280]

Re: rapping

West Marine or Autozone?