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Resolved 2gNT Alternator Tension Question

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RallyEclipse98

15+ Year Contributor
967
28
Jul 31, 2007
Dallas, Texas
'99 420a.

I'm throwing on a new alternator belt and I have it on and all bolts are on. The belt is appropriately tight but the back bolt that has its head facing the firewall is not torqued very tight. The FSM says 40 lbs. I believe and I'm probably around 20. When I attempt to torque it tighter, the belt gets too tight. Should I just ignore the factory torque spec and call it job done? The other two bolts that affect the belt tension are torqued to factory specs.

Thanks for any help!
 
No, that's an incorrect tensioning proceedure. :nono: The '99 Mitsu factory service manual says for your NT that belt should have a deflection of 0.35-0.47 inches when pressing the middle point of the belt with 22 lbs of force.
[In case someone wants to know, the turbo spec is almost identical: 0.31-0.42 inches at 22 lbs.]
 
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A trick I do is to do the quarter twist on the belt: If the belt can't be twisted a quarter turn, it's too tight and more than a quarter turn - too loose.

That's even with any belt - with grooved, toothed and "V" variety.

Another method, being a variable to the above mentioned, is the quarter inch deflection between two pulleys on the tension side-the side that "pulls" the pulley around. Classic example is timing belt tension with a clockwise belt travel: if the tensioner is on the left side of the belt travel, the quarter inch deflection is measured on the "pulling" or opposite side.

-DSM
 
Does the bolt with its head against the firewall thread through something or does it just apply tension to the bolt that threads through it in the opposite direction?
 
A trick I do is to do the quarter twist on the belt: If the belt can't be twisted a quarter turn, it's too tight and more than a quarter turn - too loose.

That's even with any belt - with grooved, toothed and "V" variety.

Another method, being a variable to the above mentioned, is the quarter inch deflection between two pulleys on the tension side-the side that "pulls" the pulley around. Classic example is timing belt tension with a clockwise belt travel: if the tensioner is on the left side of the belt travel, the quarter inch deflection is measured on the "pulling" or opposite side.

-DSM
Those are good quick and easy tests (and even widely taught) but then you always have the problem of just how much force should be used to twist it one quarter turn or used to deflect it 1/4". It's not specified, so one will use whatever amount they feel like or even worse, whatever amount it takes. And the statement you always get of "until it feels right" doesn't help the novice. Don't get me wrong, even I use the 1/4 turn method. But then I know what 1/4 turn "should feel like".
 
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This video at least makes the 1/4 turn trick a little easier to get right. You can see how much force he is using and what his strength may be relative to yours (at least based on his build). Not precise by any means but better than reading about the technique.
 
Some gauge measuring alternatives to the 1/4 twist or 1/4" deflection (or 1/2" or 1" depending on who you listen to) methods in post #3 above. For those who insist on a gauge because they are uncomfortable with any thumb/fingers method (or who maintain you can twist or deflect as much as you want without knowing how much force to use), here are some alternatives:

1) $13 - Krikit (measures tension): Gates® 91107 - Krikit V-Belt Tension Gauge | O'Reilly Auto Parts (proceedure: http://www.carbondrivesystems.com/images/uploads/forbikemaker_1301422048.pdf). I have one of these and it works ok, especially for the price. It certainly is fast. Available at Oreilly's and Napa.

2) $21 - Motion Pro belt tension gauge (measures deflection): [ame]http://www.amazon.com/Motion-Pro-Tension-Gauge-08-0350/dp/B000GU33LC[/ame] (proceedure: [ame]http://www.morbark.com/service/belttension.pdf[/ame]). I have one similiar to this and it's great if you want to measure actual deflection.

Some info on Krikit vs pencil type (eg. Motion Pro) gauges: Gates Belts and Applications: Tension Gauges: Pencil vs. Krikit.

3) $100 - OTC 6673 Universal belt tension gauge (measures tension): [ame]http://www.amazon.com/OTC-6673-Universal-Tension-Gauge/dp/B000I198J0?tag=citofgamonlco-20[/ame]. I have one of these but the problem is it's too big to get it on the belt with everything in the way and belt span so short.

4) $600 - Sonic tension meter 507C: Calibrated 507C Gates Sonic Tension Meter - $599.95. The ultimate and actually uses the way Mitsu FSM recommends for their mechanics - measures vibration frequency of the belt. Things in the way or short belt span is never a problem.
 
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