Does anyone know what the correct serpentine belt tension specs are for both belts on a 4.0L? I can't find it anywhere.

 

See page 17

 

Thank you. It looks like:

NA Engine Generator/Water Pump:
New belt = 556-578 N
Run for one minute, allow belt to cool and reset to the in-service setting. In service if tension falls below 356 N, reset at 511-534 N.

Superchanged Engine Generator/Water Pump:
New belt = 560-600 N
Run for one minute, allow belt to cool and reset to the in-service setting. In service if tension falls below 335 N, reset at 405-445 N.

AC Belt:
New belt = 556-578 N (no retensioning required)
In service if tension falls below 245 N, reset at 378 to 400 N

Supercharger Belt:
New belt = 993-1033 N
Drive the vehicle for 10 minutes, allow the belt to cool to ambient (aprox 1 hour) and reset to the in-service setting. In service at 16000 kilometer (10000 mile) intervals, reset at 835 to 875 N with the belt cold. Renew belt at 48000 kilometer (30000 mile) intervals.

I'm confused about "reset to in-service setting". Is "in-service" or below the tension at which the belt is considered to be "in service" aka not tight enough?

 

New belt stretch and what it's expected to settle down to ?

Overtight puts stress on the bearings which can be costly

 

I guess I didn't really know what this instruction meant:

"Run for one minute, allow belt to cool and reset to the in-service setting. In service if tension falls below 356 N, reset at 511-534 N."

I am interpreting that as "Run for one minute, allow belt to cool. If belt tension falls below 356 N, retension the belt to 511-534 N."

 

Looks to be a step double stretch if the first stretch doesn't " settle in "

As a rule of thumb cumming up from a lower tension which is less stressful on the bearings I just use the thumb deflection by feel

Aircraft on flight control cables are different that it must pass someone else's inspection signature at the specified tensions but a car is not

There is a critical belt length / dimension on the X300 alternator belt as some have found the amount of adjustment throw not being enough for too long a belt obtained from their source

I do have a Jaguar stamped belt that I obtained the dimmention from and is not installed so would have to measure it again

Off the top of my head both Jaguar stamped belts ( other being the A/ C belt ) are the same length , just the number of ribs

 

Thanks for the tips Parker. Yes thankfully this is not an aircraft!

I installed both belts yesterday, used ACDelco parts for both (I work for GM). The alternator belt was a pain to install as like you said, there was not a lot of throw in the adjustment rod (I think that's what you were saying?). The adjustment rod was ramming into the electric air pump bracket. Eventually I was able to work it back and fourth enough to get it in.

I ran the engine for one minute with the new belts at the high end of the tension spec. Then I retested only the alternator/water pump belt and found the torque had dropped to about 365 N (82 lb force). This was juuuust above what the manual said I would have to retension it for, I'm glad I started with the high spec on that one.

For people reading this thread for info on this job, FYI, the tension rod for the idler pulley on the AC belt uses a 1/4" square drive. Don't risk stripping it out if it's corroded. I used a 1/4" drive 8mm socket in reverse with a 3/8" drive 5/16" hex key socket (NOT reverse).

 

I had to remove the whole A / C idler pulley bracket assembly and work the long adjustment bolt loose as i was rounding out the 4 sided head with vise grips

This took some heat , penetrate , and wire brush on the threaded square in the middle of the assembly

https://parts.jaguarlandroverclassic.com/parts/index/part/id/C50.C5012.C5012212.C50122125169/brand/jaguar/