fan belt deflection pressure question

[47silver]

does anyone know how much torgue or pressure that is needed to deflect the fan belt to the specified distance? I made a tool to measure this but dont know the correct torgue to apply
thanks in advance

gary

[Rot 911]

I've never heard of anyone using a gauge to measure deflection on a 911. A 944 yes. Just push in 1/2 way between the pulleys and you should have about 1/2" of deflection. A bit looser is better than a bit tighter as you don't want to wear out your alternator bearings.

[47silver]

Kurt:

thanks for the reply, but there are a lot of people, including myself who are not sure how much force they should use on the belt to push it in. It seems like a sensible thing to measure it so that the alternator bearings are protected and the fan moves the amount of air that it is supposed to move.
I guess i could take some samples but i thought with Porsche they would have that spec'd out.
gary

[Fast Corners]

Standard thumb pressure is not specific enough? LOL.

The key is that the belt should be tight enough so that it will not slip nor should it be too tight that it causes the bearings in the alternator or the belt to wear out pre-maturely.

[47silver]

fc
yes that is why i thought there would be a specification for it, my tool uses a torque wrench to gauge the tension, works nicely, but i dont know what is should be

[mca]

I wondered the same thing as well. There really is not definitive answer.

I was running with 2 shims in and 4 out and was able to get a deflection of more than 1/2 inch ... this was done in the middle of the pulleys with a good bit of force using my index finger.

That was too loose b/c my alternator light came on.

I changed to 1 shim in and 5 out. Seems VERY tight to me. With a good bit of force I can get the deflection to fall between 1/4 and 1/2 inch (where it should be).

A single shim really makes a difference.

Basically, if it is too loose your alt light will indicate that the belt is slipping. Then, make a 1 shim adjustment and all should be good.

[WERK I]

I recommend the 1/2" deflection, but make sure you measure that value after the engine has been up to operating temperature. If you do it cold, the belt is going to be too tight when the temp comes up on the engine and you'll be wearing out alternator bearings.

[Hugh R]

I alwys adjust it tight enough that you can rotate the ending with the grabbing (hook) tool that comes with the car.

[Formerly Steve Wilkinson]

You mean you can rotate it with the tool so that the belt turns the crank, or that you can rotate it while the belt remains stationary? Big difference.

[Dixie]

You mean you can rotate it with the tool so that the belt turns the crank, or that you can rotate it while the belt remains stationary? Big difference.

But which is right? Fess up Steve. What's the right answer?

[Hugh R]

I do it just so that the crank rotates. Otherwise, how could you adjust the valves? Granted you could have it looser and take the plugs out. What's correct? I just checked and I can rotate the crank with the tool, and I have about 1/2" of play pushing with one finger.

[RoninLB]

I'm an outlier on this one

[47silver]

here is an example of a vbelt tension tool...0/35psi

[47silver]

this one is 30 to 160, i was justing using a straight edge and a bolt to depress the belt using a torque wrench on the bolt

[SteveinTO]

My method is to run it loose until it squeals like a '52 Pontiac with a 15 year old belt on a power steering pump with 30 year old oil that has congealed to grease. Then swap shims one at a time until things quiet down. Maybe go one more shim past quiet. Then you have max looseness to protect your alternator bearings and minimum tightness to always spin the fan. This method requires you occasionally roll down the window and listen to what's going on back there under load, especially if you're starting with a new belt.

Is there a flaw in my genius here? Always curious. And yes, I know, when it's squealing, the fans isn't turning well, if at all.

[pwd72s]

Originally Posted by RoninLB

I'm an outlier on this one

HOOT!

I'll confess to having been a bit of a tool junkie, and overkill when it came to carrying spares...but a tensioning tool I never had.

[Gunter]

Originally Posted by Hugh R

I do it just so that the crank rotates. Otherwise, how could you adjust the valves? Granted you could have it looser and take the plugs out. What's correct? I just checked and I can rotate the crank with the tool, and I have about 1/2" of play pushing with one finger.

I squeeze the belt so I can rotate the crank with a large socket on the fan pulley nut for valve-adjustment.

As for belt tension, I prefer to be on the lose side to save the bearings.
To prevent slipping, rub a little belt dressing on the V-sides.

We used belt dressing a lot in Industrial applications to prevent slippage and also extend the life of the belt.

[47silver]

Factory Tool P-9574 - 911 Belt Tensioner Gauge this is like the gauge shown above but is apparently a factory porshe tool

[oly]

47silver,

Did you ever find an answer to your question? Specifically, what load do you put on the belt to check the deflection?

[47silver]

i have the info somewhere and i purchased one of the tools from napa for ?? 10 bucks...

i will try to find the specs