Engine knocking noise

[seaswirl97]

Hello I have a 4.3L Gi Volvo Penta. I started having knocking noise coming from the rear of the engine(most of the noise is while the engine is idling). While reving up the engine the noise is drastically reduced. We removed the stern drive (to make sure it was not making noise from the drive) and attached a water hose for cooling and ran the engine for a few minutes but the knocking noise is still there. It sounds like a ball bearing noise going bad. We can't pin point where the noise is coming from.

The engine oil is perfect, it idles fine, revs up smooth, no major engine vibration.

Any help would greatly be appreciated

Thank you

 

[tburda]

Re: Engine knocking noise

My dads boat was doing this, it ended up being the flap in the exhaust that keeps water from backing up into the motor, check to see thats free swinging and operating properly.

 

[seaswirl97]

Re: Engine knocking noise

How do I check that flap and which part of the exhaust is it located in?

Thank you

 

[BassnTruck]

Re: Engine knocking noise

Do you have a automotive stethoscope? Or a medical one you can make work. Will make this problem real easy to pinpoint. In a pinch you can use a long screwdriver and place it to your ear. Just listen for the notice you are hearing untill it gets very loud and it will be in that area. You will hear a lot of other noises you may have never heard before also.

 

[seaswirl97]

Re: Engine knocking noise

Yes I have one and I was going to use it today.

 

[seaswirl97]

Re: Engine knocking noise

I took off the exhaust on both sides and found the metal rod that holds the flap in place. Both sides have the rod in place but no flap. I checked the inside of the exhaust pipe and did not find the flap. The metal rod that is there is thinner than the hole on the exhaust pipe and does seem like it rattles. I'm going to seal the holes and put masking tape as said by Volvo.

 

[seaswirl97]

Re: Engine knocking noise

ok put it back together and it still makes the noise. It sounds like something is hitting the bell housing. When I give it just a little gas to where it pulls out of idle it will go away drastically.

Will the coupler some how make this knocking noise if it is out of alignment or damaged?

I used a stethoscope and most of the noise is coming from the bell housing.

 

[boat127]

Re: Engine knocking noise

gimbal bearing

 

[seaswirl97]

Re: Engine knocking noise

gimbal bearing

We have removed the stern drive, so the gimble bearing is not even moving.

 

[seaswirl97]

Re: Engine knocking noise

ttt

 

[seaswirl97]

Re: Engine knocking noise

I found the knocking noise. I have not taken the engine off yet but found that the fly wheel is loose. It's banging around in the bell housing. I'm going to take out the engine soon to fix this.