How tight should alternator drive belts be?

[HuskyMan]

I've got the 1984 300DT up on ramps and am about to adjust the alternator belt tension. When I press down in the middle of the belts, I can push approximately one inch. I'm thinking the belts should be adjusted so they can only be depressed approximately 1/2 inch. Thoughts and suggestions are appreciated.....

[tangofox007]

Without a tension gauge, you are just stabbing in the dark.
Buy a tension gauge.

http://www.gates.com/products/automotive/tools-and-sales-aids/professional-tools/krikit-v-belt-tensioner-gauge

[HuskyMan]

just checked, Napa has this low-priced version....would it work for this particular application?

https://www.napaonline.com/en/p/NBGKR2

[HuskyMan]

I need to put this car back into service. Would 1/2" tension measured with my hand in the middle of the belt suffice?

[Diseasel300]

Every automotive book I've ever picked up has said 1/2" deflection under moderate pressure in the middle of the widest span. Is it as accurate as a tension gauge? No, but it'll get you home.

[pj67coll]

A tension gauge would be best but about a half inch by finger would suffice. It's how I've always done it and just did last month in fact when I changed my P/S pump and had to re-tension the two belts.

- Peter.

[HuskyMan]

Great, thank you for the update. Time to start wrenching!

[Diesel911]

I have never used or scene another mechanic use a belt tension gauge.

What I have generally observed is that if you adjusted the belt too loose and it does not squeal it will deflect obviously more then it did when it is hot.

If you over tightend the when it gets hot the belt does not deflect much more then it did when it was cold.

[Bengoshi2000]

1/2 inch deflection like those above stated. In 25+ years of doing my own work I've never used a gauge and the half-inch rule hasn't caused a component failure.

[t walgamuth]

I like them a little loose to save the bearings in the alternator. I tighten if they squeal. Of course on the newer cars with the serpentine belts all that is done for you.....great until it fails.

[tangofox007]

Originally Posted by HuskyMan

just checked, Napa has this low-priced version....would it work for this particular application?

https://www.napaonline.com/en/p/NBGKR2

That model is for v-ribbed serpentine belts. For v-belts, use this one:

https://www.napaonline.com/en/p/NBGKR1

[tangofox007]

Originally Posted by t walgamuth

Of course on the newer cars with the serpentine belts all that is done for you...

That's not necessarily true. Not all serpentine belts feature automatic tensioning.

[t walgamuth]

Originally Posted by tangofox007

That's not necessarily true. Not all serpentine belts feature automatic tensioning.

I don't see how that could work.

[tangofox007]

Originally Posted by t walgamuth

I don't see how that could work.

In that case, you woud likely blow a fuse attempting to contemplate the characteristics of a stretch belt.

Believe or not, plenty of serpentine belt configurations feature adjustable tensioners.