3.0 GM Mercruiser Noise

I purchased this boat recently and it has been making this distinct sound. I made a video of it so you can listen at this Utube link.

http://www.youtube.com/watch?v=fD-xSG3jfvw&feature=youtu.be

I have been reading the forums and read a lot about the valve lash adjustments. I just finished doing those and the engine sounds the same. The motor is the 3.0 GM, 1992. It runs great at all RPM and the boat only has about 50 hours on it. It is like new. I have listened with a pipe and a hose and can't seen to narrow down where that noise is coming from. At idle it resembles a diesel. I also removed the plug wires one at a time with it running. No change in the sound as I have heard that if the sound gets quieter that would indicate pehaps a bad bearing or crank bearing. I have read on some posts that this could be the fuel pump. I am going to pull the fuel pump but was wondering if there was something to look for when I got it out that would clue me in that it is what in the fuel pump is making the noise.
Any advice would be appreciated.
Ed

Re: 3.0 GM Mercruiser Noise

Sounds like a rumble more than a knock, small end bearings maybe

Mercruiser Alpha I, Timing Chain Noise

Mercruiser Alpha I, Timing Chain Noise

Just purchased this boat. The motor is the 3.0 GM, 1992. It runs great at all RPM and the boat only has about 50 hours on it. It is like new. I have listened with a pipe and have narrowed it down to the area behind the timing chain cover. I removed the belt to rule out the alternator and water pump and it is definately behind the timing chain cover. When I adjusted the timing earlier I noticed part of the proceedure is to jumper out the shift switch on the valve cover. This lowers the RPM and this was the first time I was able to make the noise mostly go away. Remove the jumper and noise is back. It is that steady dunk-dunk-dunk.......about 2-3 times per second at idle. Here is a link to a video so you can hear it.

http://www.youtube.com/watch?v=fD-xSG3jfvw&feature=youtu.be

This engine is practically brand new but 20 years old. Wonder if there is a hydraulic chain tensioner that is not working or plugged. I am in the course of running some engine flush through it. Going to run it some more and if the noise does not go away I guess I will have to pull the water pump and timing chain cover to investigate unless someone has a better idea.

Re: Mercruiser Alpha I, Timing Chain Noise

Re: Mercruiser Alpha I, Timing Chain Noise

I merged both of your threads together, please don't post more than one thread on the same subject.

Pull the valve cover and look for loose rocker arms to start with.

Re: Mercruiser Alpha I, Timing Chain Noise

Re: Mercruiser Alpha I, Timing Chain Noise

Don S said:

I merged both of your threads together, please don't post more than one thread on the same subject.

Pull the valve cover and look for loose rocker arms to start with.

Click to expand...

It would be helpful if we (authors/posters) had a way of deleting posts. I was so far off the real problem in my first post that I wanted to start a new one. I did the valve lash adjustment last week. The noise is still there and when I timed the engine today I finally learned the real source of the noise was the timing gear cover. I read the Clymers today and learned it does not have a timing chain but instead a timing gear. Difficult to understand what could be making that noise from in there. This engine has so few hours on it.