Noises on 4.3 Mercs

[badcarma58]

I have twin 4.3 liter Mercs, 1987, 205 hp, 262 CID.

The port engine seems to be operating correctly. When the motor is revved up, and brought back down quickly, there seems to be a knocking noise for a brief second. The motor runs and idles fine. The starboard engine does not make this noise.

Does anyone have an idea of what it may be? ...Valves knocking, maybe? Is this something to worry about?

 

[searay3]

Re: Noises on 4.3 Mercs

When were the drives pulled, ujoints inspected and serviced? If thats been done, have someone drive it and try to isolate where the sound is coming from. Front, back, high low.....since you have twins, I will guess it is in a slip and not on a trailer...If something is knocking I would not dismiss it until it is located..

 

[RogersJetboat454]

Re: Noises on 4.3 Mercs

I have twin 4.3 liter Mercs, 1987, 205 hp, 262 CID.

The port engine seems to be operating correctly. When the motor is revved up, and brought back down quickly, there seems to be a knocking noise for a brief second. The motor runs and idles fine. The starboard engine does not make this noise.

Does anyone have an idea of what it may be? ...Valves knocking, maybe? Is this something to worry about?

How does the oil pressure look on the port engine? Is it lower than the starboard? Does the needle fluctuate allot?

If you want to isolate the noise, go to an auto parts store and pick up a mechanics stethoscope, or use a long screw driver and put your ear against the handle. Go around the engine with the stethoscope or screw driver, place them in different spots and listen. Have some one rev the engine to make the noise happen. You may be able to isolate where on the engine the noise is coming from and get a better idea of what to focus on.

If the noise is coming from the lower half of the engine, my bet is one of the rod bearings may be giving up. If it is coming from the upper, you are looking at a valve train issue.

 

[NHGuy]

Re: Noises on 4.3 Mercs

Maybe it's the exhaust flaps. You can do a makeshift stethoscope by holding a big screwdriver from your ear to the upper parts of the exhaust y pipe. The flaps are just inside the upper y pipes. Listen there, if it's that you have a short dollar repair.

 

[badcarma58]

Re: Noises on 4.3 Mercs

The drives were both serviced this spring. My dad said that it was doing that last fall before pull out also.

I was playing with the throttle tonight and the knocking sounds are mainly in rear of the engine near the coupler area, and seem to be inside the engine. I couldn't place high or low

 

[badcarma58]

Re: Noises on 4.3 Mercs

I was out on the boat today.

The noise exists when out of gear only. When the drives were in Forward or Reverse, and the throttle was quickly engaged and decreased, the noise / knocking wasn't there.

When put back into neutral, and just the throttle was quickly increased and decreased (revved), the knocking was still present.