Alternative belt tension

[SoCalDMC12]

Hi all... Can anyone tell me how to loosen up the tension on the alternative belt? My a/c belt needed to be switched out, so I figured I'd do the alternator belt at the same time, but can't figure out how to give the belt some slack.

[Josh]

The alternator is the tensioning mechanism. loosen the two bolts on the alternator and the one on the timing chain cover. Just a turn or so will do. Tensioning it is a bit of a bear, I use a crowbar lol.

If you have loosened the bolts and the alt is staying put, it just needs a few love taps with your favorite rubber mallet.

[Jonathan]

Disconnecting your battery beforehand is a good idea too.

[SoCalDMC12]

Thanks, guys. I was able to loosen up the alternator before I saw your replies.

I did disconnected the battery, then loosened up the bolt connecting the bracket to the front of the engine... allowed me to move the alternator just enough to get the belt off. Re-tensioning really was a bear. It looks like I can deflect the belt with my finger by about 3/4" (maybe less)... does this seem tight enough?

PS: Yeah, I disconnected the battery... seemed prudent. :-)

[David T]

Thanks, guys. I was able to loosen up the alternator before I saw your replies.

I did disconnected the battery, then loosened up the bolt connecting the bracket to the front of the engine... allowed me to move the alternator just enough to get the belt off. Re-tensioning really was a bear. It looks like I can deflect the belt with my finger by about 3/4" (maybe less)... does this seem tight enough?

PS: Yeah, I disconnected the battery... seemed prudent. :-)

To check the tension try turning the alternator fan with the motor off. It should just turn, slipping the belt. Over tensioning the belt is bad. It will whine and prematurely wear the bearings in the water pump and alternator.

[SoCalDMC12]

To check the tension try turning the alternator fan with the motor off. It should just turn, slipping the belt. Over tensioning the belt is bad. It will whine and prematurely wear the bearings in the water pump and alternator.

Thanks, David. Seems to work just as you described above.

[SoCalDMC12]

I decided to take my D out for a shakedown cruise today (after replacing my a/c compressor and alternator belts yesterday). I got about a 2 miles out when I started to hear some squeaking from the engine. It got louder when I hit the gas, so I decided to pull over to inspect the engine bay.

Everything looked OK, though I noticed a faint squeaking at idle. I figured I’d just turn around and go home, but as I pulled away, the squeaking stopped, and everything seemed normal again.

18 miles later, I’m sitting at a Starbucks in beautiful Malibu, enjoying a delicious Mocha Frappocino, and wondering if I screwed anything up, or if a little squeaking is normal at first. Any thoughts would be greatly appreciated.

[Rich]

Increase the belt tension. It's now slipping (a bit hotter than after first installed) and causing the squeal.

Don't overdo it. Shoot for ~1/2in. deflection midspan with heavy thumb pressure. As pointed out too high on tension is bad for components but slippage for a long time will glaze the belt. And the noise will drive you nuts.

Worst case drop by any repair shop with a belt tension gauge soon and have them adjust it. Minimal charge, maybe half an hour's labor. The v-belts on a D aren't anything special.

[SoCalDMC12]

Increase the belt tension. It's now slipping (a bit hotter than after first installed) and causing the squeal.

Don't overdo it. Shoot for ~1/2in. deflection midspan with heavy thumb pressure. As pointed out too high on tension is bad for components but slippage for a long time will glaze the belt. And the noise will drive you nuts.

Worst case drop by any repair shop with a belt tension gauge soon and have them adjust it. Minimal charge, maybe half an hour's labor. The v-belts on a D aren't anything special.

Thanks for the input, Rich. Now that I have been properly caffeinated, I can go home and re-tension the belts.

[David T]

Thanks for the input, Rich. Now that I have been properly caffeinated, I can go home and re-tension the belts.

If it is not from a belt being loose it could be a bad bearing. First to check is the idler bearings for the A/C belt. Next is the alternator and then the water pump.

[SoCalDMC12]

Well, looks like there was a bit more slop in the ac belt, so I tightened it up a bit. Ran it for a while in my garage, and no squeaks... Will take her out for another shakedown cruise tomorrow (just need another excuse to take her out). Thanks again, all!