V-belts and underdrive pulleys...

[2ndgen]

The crank pulley on my engine was in bad shape and I found a good deal on a billet aluminum crank pulley that is a slight (0.85) underdrive. Since I am running a loose converter and low gears I thought "No problem!"...

I find now that the stock belts are a bit loose with the power steering and alternators at the maximum adjustment. Can anyone point me to a catalog or interchange manual that specifies belt length? Does anyone happen to know the next sizes down from the stock 351W belts on a non-air car with power steering?

It's a bit embarrassing to have my new engine sound overpowered by belt squeal when I park the car...

Thanks in advance,
-Rory

 

[AzPete]

I would just buy a belt about 1" shorter. The auto parts should be able to help you on that. Otherwise, set the units where you want them to be adjusted to and measure the belt length and purchase that size.

 

[gotstang]

The belt lengths are hidden in the part numbers, and if you're lucky, you should be able to read the numbers right off of the belts. Then, you can go to a good shop (ie. NAPA) and ask for one 1/2"-1" shorter. We just did this dance with a 5.0L Mustang and it took seven trips to NAPA to get it right. But we *are* idiots :lol

 

[miketyler]

You probably already know this but underdrive pulleys are ok on most cars but on a car that runs a "little hot", they can be the kiss of death as they turn the waterpump slower.

 

[buening]

I took my belt off and brought it into a parts store and told them I needed one just like it but a few inches longer. They were able to hook me up and should be able to do the same for you.

 

[Jonk67]

Post your 2 belt numbers and we'll be able to give you numbers that are the next shorter length. Most common numbers such as Gates should be 7390 for alt. w/ps w/o ac and 9530 for fan and ps w/o ac according to their website, guessing it's a '70 351W? It helps to have your car vitals in your sig for questions like this.

In this case the 7390 is 7(39.0) is a 39" belt and 7 is their width for this belt. The 9530 is 9(53.0) 53" belt with a 9 width.
A 7385 will be 38.5", 7380 will be 38", etc. if you want to try 1" shorter on each get 7380 and 9520. Keep them from getting greasy, don't trash the box and you can always take them back and swap them for 1/2" shorter/longer. It's the full length of the belt if you cut it so it will only take ~1/2" from the pulley's throw by shortening the belt 1".

Many companies use 5 numbers but the break down is similar, the length and width will be hidden in there.
Jon

 

[2ndgen]

Thank you! this is just the info I needed... according to my math the circumference of my underdrive pulley is 2.6 inches shorter, but since the belt does not go all the way around I will try belts that are 1.5 inches shorter. Just called the local O'reilly's and they have the two gates belts I want to try in stock...

-Rory

 

[daveSanborn]

Although stated, but not explained, if you run a length of your typical 50' extension cord around the pulleys mimmicking the belt routing.... and then measure the distance it takes to complete the "loop".... you'll know exactly what length belt you'll need.

 

[miketyler]

I put March pulleys on my Cuda along with custom AC brackets. The Sanden AC was a dual belt design and I had much the same issues. It was hard for me to gauge the size I needed with the limited adjustment on the alternator. It quickly became a matter of taking the belt that was too small to the auto parts store and buying several belts the next 2-3 sizes larger.