engine knock caused by failing alternator

[JGXJ]

At idle and off throttle while driving, a failing alternator bearing was producing a very noticeable knock. Sometimes it sounded more like a rattle.
But it never squealed. Alternator replaced. Now I can actually hear a slight rod knock and sticking lifter. On to the next project.

 

[langer1]

Might want to try it with the belt off and see if all the knocking goes away.

 

[Dr. Dyno]

On to the next project.

Is that to build a stroker?

 

[DaveW]

Sorry to about resurrecting an old thread but I had the same problem this week.

A rattle or scrapping sound started. IT seemed to come from the lower middle to back of the engine. I thought is might be loose torque converter bolts but they were tight and the flex plate was not cracked.

I use a hose/stethoscope to find the noise but could not find any one place where is was significantly louder. I could hear the rattle/scrap sound though the oil pan best.

I was thinking the engine might be on it's last legs. The noise had become loader over a couple of days. When I get a phone call from a friend who was also unable to identify the source. He was on his way to tow his XJ home because the bearings on the A/C had gone out. The sound was very similar to to the one plaguing me. At first is sounded like it was coming from the back of the engine.

So with the sound now louder I went over every thing again with the hose/stethoscope. I could hear the sound at about they same volume from the alternator as from the oil pan. The rear bearing of the alternator was obviously bad. (After 20 years I did not feel bad replacing it)

It is amazing how sound and travel and echo though an engine.