Serpentine idler adjustments?

Hey All,

When replacing the serpentine belt (4.0 I6), how tight should the jackscrew on the idler pulley be? I replaced it once at 40K miles and set it to what I thought was sufficient. I'm now nearing 80K and I've got the ominous squeak telling me it's time again. I feel I should probably get this right this time.

Also, it's time for the "big" service again (cap, rotor, plugs, wires, brakes, etc...) and I'm wondering about brake rotors. I've heard that they are un-cuttable past a certain point. They are the original rotors and I'd like to replace them but $$$ is tight.
What is the letter of the law on XJ brake rotor cut limits?

Thanks,

-Sticks

It almost certainly needs to be tighter than you think.

It might be worthwhile going to NAPA and ordering the Krikit II tension gauge for about 12 bucks. You may have to convince the people there that such a thing exists. It does, and they can order it.

In the meantime, a good rough gauge is to try twisting the long span of belt that you can reach on the top. It should be just possible to twist it 90 degrees with your hands, but no more.

By the way, I'm assuming that you are just being imprecise in language when you refer to the "jackscrew on the idler pulley," but just in case.... The belt is adjusted by moving the entire power steering pump with the jackscrew, so don't forget to loosen the various screws that allow it to move, or you'll find it very hard to tension, and end up breaking the jackscrew.

I'll add my 2 cents on rotors. I would question whether they should be replaced or turned at all at 80K miles, unless there is a problem. A good rotor can easily last over 100K miles., especially if you live in an area where roads are not salted much. Brake shops have some obessive-compulsive need to turn rotors, but an evenly worn rotor that doesn't shake or shimmy won't work any better after turning. It will just have its lifespan shortened by thinning. Aside from being brought that much closer to its wear limit by the machining, a thinner rotor will warp more easily under duress. I would hesitate to put rotors that have been turned near to their limits on a vehicle that tows, for example. Aside from that, the tolerances are so close that unless the rotor is turned on its own hub there's a chance they'll make it worse. If I were you, I'd run the original rotors until they are either truly worn out or until they start to shake, then spring for new ones.

If you insist on turning, here are the limits according to Haynes (note source, and apply grain of salt as needed....)

Up to 89 = .815 in/20.7 mm
90 = .94 in/ 24 mm for 4wd
91-up = .89 in / 22.7 mm for 4 WD

The 95 FSM also specifies .89/22.7.

Rotor should be marked, and marks supersede these figures.

.004 inch (.10 mm) runout max for all

Actually, the problem is that "sticks" didn't specify a year. Most XJs with the 4.0L adjust the belt tension at the power steering pump, but the late models use a much easier to adjust tensioner.

Once again, folks, if you want an answer to your question that applies to your vehicle, it is best to provide some basic information such as year and engine.

Oops.

1998 XJ "Classic". 4.0 I-6, 72K miles (specifically).

Sticks

On my 98 the belt is tensioned by an idler pulley to the left of the PS pump. I almost loosened up the PS pump but decided to look at my FSM for their procedure. When my belt was tightened to specs with the krikit II gaguge I could only deflect the belt about 1/4". I set it for 190lbs.

Yep - my '96 has the same idler pulley just below the power steering pump. Remember to just losten up the idler pully a tad as that lets the tensioner move. Once you have it adjusted, re-tighten up the idler pully.

Tom Dennis