Noob Alert: squealing belt

[gravyface]

Hello all,

Belt's been squealing loudly pretty much all winter long, but decreases/stops once the car's warmed up or when I'm up around 2k RPM.  I'm thinking it's the accessory belt as when it's squealing, there's a noticeable decrease in the air flow from the vent: once it stops squealing (if I gun it a couple of times, it'll "catch") the air flow increases.

I looked at the belt, it doesn't look too cracked/worn out or anything (but I might not be inspecting it correctly), could it be a pulley/guide?  Is there a way to adjust the belt tension?

[DesktopDave]

It's probably the alternator belt.  When you rev the engine it heats the belt up enough to grab the pulley.  Then you get enough power to spin the fan motor at it's proper speed.  I test the belt tension with my thumb.  When I press hard in the middle of the longest span, it should deflect the belt less than a half-inch (~2cm).  Not much at all, in other words.

If the belt is loose, find the alternator support bracket.  It has a gear pattern stamped into it.  The alternator is bolted to it.  Loosen the nut on the rear of the alternator (13mm) and the bolts at the base (also 13mm).  Then get a 17mm wrench & turn the large nut.  It will tighten the belt.  Don't overtighten that, it's easy to srip the gears on the bracket.  If they're already stripped, use a prybar or large screwdriver to pry the alternator out instead.  Then tighten everything up & test the tension again.  If you run out of space and the belt is still loose, replace it.  They can stretch over their life, and cheap parts are usually not sized correctly.

My e30 only has one belt left...the water pump/alt belt.  I've pulled the other two!

[gravyface]

It's probably the alternator belt.  When you rev the engine it heats the belt up enough to grab the pulley.  Then you get enough power to spin the fan motor at it's proper speed.  I test the belt tension with my thumb.  When I press hard in the middle of the longest span, it should deflect the belt less than a half-inch (~2cm).  Not much at all, in other words.

If the belt is loose, find the alternator support bracket.  It has a gear pattern stamped into it.  The alternator is bolted to it.  Loosen the nut on the rear of the alternator (13mm) and the bolts at the base (also 13mm).  Then get a 17mm wrench & turn the large nut.  It will tighten the belt.  Don't overtighten that, it's easy to srip the gears on the bracket.  If they're already stripped, use a prybar or large screwdriver to pry the alternator out instead.  Then tighten everything up & test the tension again.  If you run out of space and the belt is still loose, replace it.  They can stretch over their life, and cheap parts are usually not sized correctly.

My e30 only has one belt left...the water pump/alt belt.  I've pulled the other two!

Thanks (as always) for your detailed response, Dave.  I'll give this a go.

[dakon]

Gravy, thanks for making this post.. Dave thanks for your wonderful answer... I have the "exact" same issue, but wasn't sure exactly how to fix it.

[DesktopDave]

Anytime. :cool:

I'll blab on all day if you like!