Alternator belt tension

[CoupeWannabeS2]

Managed to lose my alternator belt - noticed it was gone after the battery light came on, and the voltage dropped.

Thankfully I got the car home under its own steam, which was a trip of about 40 miles, with the battery gradually dying.

Anyway, can anyone advise how to get the tension correct on the replacement? I noted that the alternator can move left and right to tighten the belt, but not sure how tight it needs to be.

[CoupeWannabeS2]

After some internet searching, i've found references to holding the belt, and attempting to turn it (that is twist it). Ideally you should be able to turn it between 45 and 90 degrees. More than 90 degrees is too loose, and less that 45 is too tight. Can anyone confirm if this is a safe way of checking the tension on an ABY S2 alternator belt?

[K Simmonds]

Sounds about right, you should be able to turn 90 degrees in the middle of the longest run without using a huge amount of force. You want to avoid over tightening it as will place undue stress on the alternator bearings.

[CoupeWannabeS2]

Sounds about right, you should be able to turn 90 degrees in the middle of the longest run without using a huge amount of force. You want to avoid over tightening it as will place undue stress on the alternator bearings.

Cheers for that.

[Laaf]

I'd say as loose as possible without it slipping. I blew 3 belts in 2 weeks two years ago until I loosened the tension on it.

[CoupeWannabeS2]

Thanks for the input guys.

I have obtained some further info from the Audi 80, 90, & Coupe Haynes manual, that I wanted to post up, as it may be of use to others.

Firstly, loosen the alternator pivot and adjustment bolts, and swivel the alternator towards the engine.

Slip the new drive belt onto the pulleys.

Turn the tensioner rack nut to move the alternator away from the engine, until the drive belt deflection half way between the pulleys is approximately 2mm under firm thumb pressure.

In the event that a used belt is being is being refitted, this deflection should be 5mm.

Hold the tensioner rack nut in this position, then tighten the adjustment bolt.

Stand back, and admire your handy work. (I made this bit up).

[CoupeWannabeS2]

Got the new belt today - and all fitted. Got it from Car Parts For Less, which is the sister company to Euro Car Parts.

Some S2 parts are quite cheap - only £5.46 delivered.