Recently installed Original Air conversion on my Firebird and this is the belt they supplied. It appears to be a standard length belt (Dayco 945K6) but it seems pretty tight to me. I have posted a photo of the tensioner marks - can someone chime in and tell me whether this looks okay or not?

 

If it went on, it's fine. Regardless of marks.

 

That's really tight and possibly going to cause uneven wear on your front main bearing. It did on mine.

 

How much longer should I look for? Half inch? Inch? More?

 

A new belt will stretch over time. Make sure the belt is lined up right on the pulleys. It won't take much to get the marks back in line. What does the old belt look like?

 

A belt isn't going to wear a crank bearing. It'll wipe out a bunch of little light-duty 6203 which is in the front of the alt and the tensioner and idler, LONG BEFORE the crank will even be able to notice it.

If you could get it on, it's fine. That's one of the virtues of the tensioner system; it's basically impossible to overtighten the belt. It'll stretch over time anyway. That just means it'll be longer before you have to buy another one.

 

oh, hell... I'm arguing with sofakingdom. What fun this will be.
I'll preface this with saying that I'm on vacation, so I cant give photos for a couple of days. With a new tensioner, and a shorter belt I was in this maximum range. I had an issue with my rear main thrust clearance that required me to pull the lower half apart. My front upper main bearing was prematurely worn in the area that holds the load of the belt. Now it's possible that some wind pushed the crank into this area of the bearing as I drove 500mph, but I think it's more likely that a belt was too tight. Why risk the cost and hassle of main bearing damage if you can just buy a longer belt that puts the tensioner gauge into a better operating range?

 

I'm not at home and won't be for a couple of days, but I had to guess on mine twice to get it in a better range. Just run up to your parts store, tell them what you're doing and they'll probably let you try 1 or 2 in the parking lot. Try moving up in size by 10mm or so at a time. You may already know, but here's how to decipher the belts PK number from Gates website.
https://www.gates.com/resources/resource-library/tech-tips/read-a-pk-number-on-a-abds-serpentine-belt

. HOW DO I READ A “PK” NUMBER? The PK number is broken down into three pieces of information: » Number of ribs on the belt » Belt application information » Effective length of the belt expressed in millimeters EXAMPLE: 6PK1003 » 6 - This indicates the number of ribs on the belt; therefore, this is a 6-rib belt. » PK – The “P” indicates a metric designation, and the “K” indicates the belt is automotive per SAE J1459. » 1003 - This is the effective length of the belt expressed in millimeters.

 

Thanks all for the input. FWIW, about 75 miles after installing this belt, the alternator bought it. True, it was the original alternator (28 years old) but with only ~17,000 miles. And there is a subtle "tweek-tweek-tweek" when it spins, so that makes me suspicious of this belt situation. Maybe it would be okay, but I tend to be cautious about these things, so I think I'll try a 1/2-inch longer belt and see how it looks. Once again, thanks for all the comments.

 

I have to agree with Sofa on this one. No way did thay dinky little belt put any deflection on the crank. More likely the main line needs to be honed on that block. Many of these engines came from the factory with some really poor main line work and GM compensated with carefully selected bearing inserts. The belt doesn't put even a fraction of the load on the bearing that that firing of a cylinder puts on it.

GD

 

"If it went on, it's fine. Regardless of marks." only makes sense for a stock set up. My system has some accessories deleted. My current system uses a guest at 6K966 belt that is slightly lose, probably need a belt about 3/4" shorter. More information on the tensioner marks would be very helpfully. What does the reference marking and the min and max markings look like! A close up picture with the marks clearly marked would be great.