bearing noise s70

Hello,
I am hearing a knocking - tapping noise that sounds like it is coming
from one of the accessory items. The AC compressor, alternator, PS pump,
are my primary suspects. I have tried touching these items while the
engine is running to see if I can narrow it down and I can not reach the
AC compressor and can not distinguish between the others. These parts
are so close to each other and are mechanically bolted to virtually the
same place it is hard to tell where the sound is coming from by feel.
The idler and tensioner are possible too, but the noise seems to be more
forward than those parts. The car has about 130K miles on it and this is
the first of any these parts to give any trouble. It is a 98 model year.

My question is what are the best ways to narrow down the problem ? I
don't want to guess or use the shotgun method and replace them all, as
all the parts seem pretty expensive and it is a tight place to work. To
get to the alternator out, for instance, looks like the PS pump must be
removed from the car to get to the alternator, hope there is an easier
way if the alternator has to be replaced. I would guess the AC
compressor might be possible to access from below?

Funny thing is that, for now, everything seems to be working fine. I
don't want to let this go and have it strand me at the side of the road.

Thanks for all suggestions and help.

 

I am dubious it is coming from any of those items, although the PS pump is a
possibility. The A/C compressor is actually a very strong suspect except for
something you didn't mention: does the tapping go away when the A/C is off?
If so, you've found the source, otherwise, look farther. When disengaged the
A/C compressor just presents a bearing to the rotation. The bearing could
have a broken ball, but those usually result in intermittent jamming of the
bearing. Just about the same with the alternator; knocking-tapping doesn't
square well with the mechanics of it.

The P/S pump could certainly do it, but I'd be reluctant to shotgun it. Auto
parts stores (and Sears) sell a "mechanic's stethoscope" that fits a metal
rod to a stethoscope earset to help in finding noises like this. My
experience is that metallic sounds seem to be everywhere, but at $20 US or
so it might be your wisest approach at this point.

Mike

 

The noise is present with the ac off, I actally did not try listening
with the ac on as I figured the bearing was in motion even with it off
as the belt is turning the pully on the ac, I realize the ac clutch is
not engaged so other ac internal parts are not turning.

I will look into the "mechanic's stethoscope" and see if that helps.

thanks for the suggestion and quick reply too.
I look forward to other suggestions also.

 

Remove the accessory belt, start the car and see if the noise has gone
away. If it has, manually spinning the accessories, idler and tensioner
may indicate which one is bad.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)