Rule of thumb for tensioning alternator drive belt?

[LucasDK]

Hi,

Is there a rule of thumb for tensioning an alternator drive belt with the old school V-belt design? Without using a gauge but just using hands, common sense etc? I know the rule for tensioning a timing belt (90 degree twist) but how can something similar be applied for a V belt which is more "boxy" in cross section?

Lucas

 

[Ursatdx]

I tighten them so they have about 1/2" play at longest stretch.
Drive a few hundred miles and check tension again.
Some will stretch/seat a bit when used.

 

[Puhdantic]

The 90 degree twist is actually what I've seen for drive belts. Wouldn't feel comfortable spitballing a timing belt.

 

[Soft Cars]

1 inch of deflexion which I believe is a 1/2 inch in either direction. Please correct me if I'm wrong.

 

[Carmudgeon]

Stabbing at a deflection without also accounting for the length of the span doesn't paint the complete picture.

A half-inch over a 12-inch span is not the same as it is over a 6-inch span.

The best bet is to follow what the OEM specifies, but there are also generic tables to follow.

 

[meep]

If I recall, on the simple v8 I had, the top of the belt between water pump and alt could deflect 1/2” under approximately 5-7lbs of pressure.

newer vehicles seem to be much tighter.

 

[bunnspecial]

The only one I deal with regularly is on the MG, which is a single one driving the fan+water pump and alternator. I use the 90º rule. It's served me fine for quite a few miles now. IIRC the one on there now went on 2016 and has several thousand miles on it, plus has seen an up-rated alternator(65A from the stock 35A) in that time.

 

[LucasDK]

Thanks for your replies