X300 Alternator Belt Squeal - Yet again

I’ve search the archives - plenty of similar complaints but no really definitive consensus on tightness of belt.

About 6 months ago I replaced the harmonic balancer & alternator and installed a Gator belt. Car had squealed as a result of balancer failing and coincidentally the alternator gave out.

Belt is squealing again at startup and at stop lights with corresponding drop in alternator charge.

The belt can be twisted to 90 degrees. No oil on belt. I just painted across the balancer to make sure all is ok on that front.

What is the general consensus on how tight? I’ve read tighten till it stops squealing. I’ve also seen 45 deg twist referred to. I also saw this post from Kirbert here re ribbed belts:

I am also going to put a wrench on the alternator to see if it turns easily.

PS Really thought the much touted Gator Belt would do the trick. I’ve tightened it twice since I installed it.

I think a 90 deg twist is to much I would be going for a bit less than that. This is from a Gates web site;

Probably for industrial drives but in the end a vee belt is a vee belt?

You need this:

Both belts on the facelift XJS with the AJ16 are supposed to be at 50kg. If you have an AJ16, I’m sure it’s the same, but someone else here will correct me.

Hah! 20 years on, and I still stand behind that advice!

I’ve read this thread a while ago…the excellent ASCII artwork is very memorable.

Luckily I haven’t had a squealing issue with my belts…but when it happens, I was wondering if I couldn’t just shove a grindstone in there while the car was running? Instead of taking the alternator out, couldn’t I just take advantage of the spinning pulleys

Sure, if you don’t value your fingers.


Seriously, what is more plausible is to chuck up a driver in the ol’ electric drill, fit the right size socket, apply it to the big nut on the front of the alternator, and give it a spin while holding a stone or file to the pulley. Of course, the belt must be removed or at least loosened. In most cars I expect the alternator would have to be taken out of the car because there’s no room to get a drill in there. Or, perhaps remove a lot of other stuff to make room.

From what I’ve read these are designed for V Belts.

I adjusted the belt to approx 45 degree twist and no squeal this morning. Did 40 miles test drive yesterday after throttle body clean and all looks good for now. On to the secondary air valve now - see separate post.


So far so good at 45 degree twist on belt. After 2 weeks.