Torque Spec on Alternator Pulley
04-16-2012 | 09:57 PM
#1
Thread Starter
Race Car
Joined: Nov 2009
Posts: 3,526
Likes: 17
From: Ottawa
Torque Spec on Alternator Pulley
Hello All,
Ever since I got my alternator replaced I have been hearing a "rustle" that to my untrained ears sounds like a spinning part that isn't spinning freely (as if a bearing isn't smoothly rotating).
Anyway, I went to take off the fan belt tonight to see if the fan spun smoothly and for the life of me couldn't undo the nut that holds it in place (using the spanner from the toolkit and the 24mm socket).
I checked my Bentley, and noticed that it has 2 different specs for the torque on this nut in different sections. One place it says 40Nm and another it says 55Nm... a big difference.
1) What is the proper torque spec?
2) If the shop over-tightened the nut could it cause such a "rustle" when the engine is running?
On an unrelated topic, when I'm at lower rpm's and I let off the throttle I hear a raspy sound.... is this normal? I've been reading the other thread on noises - it seems us new owners are a bit paranoid with the unknown! What does your car sound like when you completely let off the throttle? The noise goes away as soon as I depress the clutch pedal.
Many thanks!
Ever since I got my alternator replaced I have been hearing a "rustle" that to my untrained ears sounds like a spinning part that isn't spinning freely (as if a bearing isn't smoothly rotating).
Anyway, I went to take off the fan belt tonight to see if the fan spun smoothly and for the life of me couldn't undo the nut that holds it in place (using the spanner from the toolkit and the 24mm socket).
I checked my Bentley, and noticed that it has 2 different specs for the torque on this nut in different sections. One place it says 40Nm and another it says 55Nm... a big difference.
1) What is the proper torque spec?
2) If the shop over-tightened the nut could it cause such a "rustle" when the engine is running?
On an unrelated topic, when I'm at lower rpm's and I let off the throttle I hear a raspy sound.... is this normal? I've been reading the other thread on noises - it seems us new owners are a bit paranoid with the unknown! What does your car sound like when you completely let off the throttle? The noise goes away as soon as I depress the clutch pedal.
Many thanks!
Last edited by porsche0nut; 04-16-2012 at 11:28 PM.
04-17-2012 | 01:45 AM
#2
Three Wheelin'
Joined: Feb 2003
Posts: 1,676
Likes: 79
From: Santa Barbara, CA
Have you taken the car back to the shop that replaced the alternator to let them have a listen to the noise? That is always the best thing to do in an "ever since they____" case. First of all, it often takes a trained ear to know what noises are and aren't normal on these engines and where the noise could be coming from. Not to mention it gives the shop a chance to make it right if the noise is related the the prior repair work. Also, if the noise is possibly related to work that they did, if they know that you have been messing with it they could say that it can't be proven whose fault it is.
That said, I would believe the higher 55 Nm spec, which happens to be almost exactly 40 ft-lbs. That may be where the confusion exists. I will check the factory manual tomorrow if I remember, as there is some misinformation in the Bentley manual. It can take some torque to crack that nut loose, even when torqued to spec, so I wouldn't immediately suspect that the nut being difficult to loosen means that it is too tight and is somehow causing the noise. But, I would check to be sure that the cooling fan isn't rubbing the housing, and that the belt tension is correct.
It is difficult to diagnose sounds over the internet, but if I had to place a bet, your "rasping" noise is gear rattle and is perfectly normal if you have a spring-centered clutch disc vs the original rubber centered one.
That said, I would believe the higher 55 Nm spec, which happens to be almost exactly 40 ft-lbs. That may be where the confusion exists. I will check the factory manual tomorrow if I remember, as there is some misinformation in the Bentley manual. It can take some torque to crack that nut loose, even when torqued to spec, so I wouldn't immediately suspect that the nut being difficult to loosen means that it is too tight and is somehow causing the noise. But, I would check to be sure that the cooling fan isn't rubbing the housing, and that the belt tension is correct.
It is difficult to diagnose sounds over the internet, but if I had to place a bet, your "rasping" noise is gear rattle and is perfectly normal if you have a spring-centered clutch disc vs the original rubber centered one.
04-17-2012 | 08:40 AM
#3
Team Owner
Joined: Aug 2005
Posts: 27,237
Likes: 1,179
From: Cambridge Ontario Canada
the over tightened nut ( even if it was ) in this case will not cause any rapsinesss in the bearing. The issue is really if the wrong amount of shims are in or the belt is too tight. That could cause the fan to rub on the housing . I guess you could have a bad bearing in a rebuilt alternator ( again if the belt was to tight ) but i seriously doubt it. Henry knows what he is doing for sure.
Why not just remove the AC belt first. it wont affect anything , you can drive around without it and you can at least eliminate the compresor clutch bearing.
Why not just remove the AC belt first. it wont affect anything , you can drive around without it and you can at least eliminate the compresor clutch bearing.
