120HP Merc, Piston slap, wrist pin, cam bearing? Video!

[Fordiesel69]

http://outdoors.webshots.com/video/3021439300044425697YgNMpo

Click above video and tell me what you think the engine sounds like. This is a stone cold start at about 53 degrees F. Out of the 3 other 4 cyl boats I looked at locally all sounded like this. I even remember my grandma's 2.5L in her buick sounded noisy like this.

What inside these engines makes them loud when they get old? Is this cam bearing, wrist pin, or just plain old piston slap. It does quiet down a little once it is warm.

 

[Maclin]

Re: 120HP Merc, Piston slap, wrist pin, cam bearing? Video!

The noise when backing down sounds like a rocker is about to come off, hard to tell, almost have to bee there to "feel" it. The differing tones between throttling up and backiong down may indicate wrist pin also. Just my opinion.

 

[Silvertip]

Re: 120HP Merc, Piston slap, wrist pin, cam bearing? Video!

Assuming oil pressure is normal, pull one plug wire at a time with the engine running. That will locate the bad cylinder if it is piston slap, wrist pin, or possibly a rod bearing. If the noise doesn't change using that technique, then pull the valve cover and look at the rocker arms and adjustment. Sometimes the rocker arm loses lubrication because one end or the other of the push rod gets plugged up and wears the rocker socket or the push rod. Lubrication gets up there from the lifter body, through the push rod and out the small hole at the push rod end of the rocker arm. If that's ok, the one must suspect not necessarily in order, cam gear, cam bearing, and do not overlook a bad fuel pump. Yes -- a weak pump arm spring which was a problem on GM fuel pumps in the past, can sound like a rod bearing. The spring does not keep the arm in contact with the plunger or eccentric on the cam and hence the noise. I am old enough to remember this problem. But do the easy stuff first. Sludge build up in the front cover of these engines was also a problem in cars that caused the same sound.

 

[Fordiesel69]

Re: 120HP Merc, Piston slap, wrist pin, cam bearing? Video!

Oil pressure is always around 40 on the gauge at speed and about 20 idle when warm.

What elese may be helpful to know is I put 5 hours on this engine at 3800RPM and the sound has not got worse. I will be putting about 1.5 on it today again and once I yabk it out for the season I will tear into it.

I find it very odd that all of the 4cyl models I looked at locally, some being 2.5L's and others being 3.0L's, they sound the same.

 

[Alumarine]

Re: 120HP Merc, Piston slap, wrist pin, cam bearing? Video!

Are you sure it's coming from the motor?

Sometimes the water shutter makes a racket.

 

[Fordiesel69]

Re: 120HP Merc, Piston slap, wrist pin, cam bearing? Video!

It sure does sound like the engine block / head. I bought it with a bad impeller, and I am not ruling out the PO overheated it. I had it to 190 myself, who knows what they had it up to.

Where would I inspect the water shutter?

 

[littlebookworm]

Re: 120HP Merc, Piston slap, wrist pin, cam bearing? Video!

Silvertip has covered all you possibilities. I also remember the problems with the GM 4-cylinder engines. They and the small blocks used to have a problem with rocker arm pivot studs pulling loose, some slightly and some completely. Some of the later engines had screw-in studs so they couldn't pull loose; however, they did wear at the pivot point creating a wobble effect to the rockers. I listened to the film a few times trying to match the sounds with my memories. My guess is a rocker arm problem amplified by the tin of the valve cover. Check that first. Pull the valve cover and run the engine at idle. Look for loose or wobbly rocker arms. Try putting some pressure on each arm in turn with your hand to see if that quiets down the noise. If so, I'd suggest pulling each rocker arm, cleaning and blowing out each rocker arm and push rod, checking the pivot stud for looseness, checking each stud, pivot, and arm itself for wear, and then re-assembling everything, adjusting the rocker arm clearances as diected in the manual. Good luck and let us know what you find. Hy