Identify this knocking noise *VIDEO*

[bob johnson]

Re: Identify this knocking noise *VIDEO*

I had a geek flash and decided to analyze the sound. It occurs at a frequency of 960 RPM, which is probably your idle speed. That makes me think wrist pin/crank bearing.
The acoustics of the recording may be fooling us because it does not sound like a crank noise to me so I'll post my guess as wrist pin.

any interference contact would have the same incidence as the rpm!!!!most likely

bob

 

[Tig]

Re: Identify this knocking noise *VIDEO*

Listen to the sound change as he walks around the engine. Much different front to back. Also at :55 - 1:05
Makes me believe that this is not coming from the flywheel since that is always unobstructed.
As a fellow boater I will be delighted if I am wrong.

Now, looking again at the video very carefully at the :56 mark. Am I seeing the fly wheel to crankcase spacing change as if maybe the flywheel was loose?
I'd expect the sound to be double the idle frequency, as it would oscillate with each power stroke. This also does not fit with what I think I am hearing, but my eyes don't seem to agree with my ears and it's cheap to check.....
I had this happen to a car once. It sounded like a bag of hammers.

 

[jonesg]

Re: Identify this knocking noise *VIDEO*

you know i have a knock in a 90 hp ocean pro...If I did your tests and all is good..IE I can't move the piston once the move goes over top dead center jst a tad...

then what else could make that knocking noise?

I have a OIS 60 degree looper...

also for the OP where would you suggest to look for another source of this internal know???

magnets under the flywheel??

will they make this much noise and still allow the motor to run?

thanks

bob

Loose magnets would trash the stator , start a thread with full description, you get lots of help here.

 

[nymack66]

Re: Identify this knocking noise *VIDEO*

Does not sound good, Could be a rod bearing its kinda like my loose rod on the v4 but I could be wrong. If this engine means a lot to you then don't be afraid to open it up and find this problem, if you don't who knows? The minute I heard my v4 started to knocking I shut her down, use my tiller to the dock open her up and bingo!

 

[boobie]

Re: Identify this knocking noise *VIDEO*

I'll post my guess as "piston slap". Could be a collapsd piston skirt. Heard this same sound in many other motors.

 

[N2outboards]

Re: Identify this knocking noise *VIDEO*

Top end bearing may be out-of-round alowing cam lobe on sector shaft to be allowing points to open or close to openly or tightly.

 

[rockfordhx]

Re: Identify this knocking noise *VIDEO*

I really appreciate all of the ideas and help that everyone is providing. I will do some work this weekend on it and post back my findings. thanks so much

 

[rockfordhx]

Re: Identify this knocking noise *VIDEO*

I had a few min today so i quickly did the dowel test with each piston. Strange thing... at least to me that is. Once the piston was all the way down I was unable to move it any further using the dowel; however.... Is it normal to find that the piston is all the way down but the flywheel is able to turn a little with no movement in the piston? It seemed like I saw some play in the flywheel when the piston was all the way down.

 

[Tig]

Re: Identify this knocking noise *VIDEO*

That's a tough one to call on the internet. The geometry of the piston to crank at BDC is such that there may seem to be a bit of a dead spot. Do you have the same "play" when the piston is half way up? That would be better place to look for slop. Even then, the slop is the total of all tolerances and issues between the piston and the flywheel.

 

[jonesg]

Re: Identify this knocking noise *VIDEO*

That's a tough one to call on the internet. The geometry of the piston to crank at BDC is such that there may seem to be a bit of a dead spot. Do you have the same "play" when the piston is half way up? That would be better place to look for slop. Even then, the slop is the total of all tolerances and issues between the piston and the flywheel.

When the cyl fires the piston rod pushes down on the crank , after bottom center the crank pushes the piston up. You're detecting the tranfer of load from push to pull as the connecting rod swaps from one side of the crank (push) to the other(pull). Is that linear to transverse? doesn't matter.

But there is a dead spot where the crank moves but the piston doesn't....BUT the connecting rod takes up the motion ...then motion is taken up by the piston again.

Thats not the test you need to perform, you want to pull the piston halfway down or ATDC then push on the piston to try to detect slop in the big or little end of the rod.

 

[Tig]

Re: Identify this knocking noise *VIDEO*

I will do some work this weekend on it and post back my findings.

and then????