Squeaky alternator belts

[Growlerbearnz]

Alternator belts that squeal for a while after startup (especially when it's cold) are usually just a bit loose. The glow plugs take a lot out of the battery, so the alternator tries to recharge the battery quickly, putting extra load on the drive belts and making them squeal. Belts that squeal for longer might indicate that the belts are worn or contaminated (oil, mud, road spray with salt or diesel, etc.)

How to tighten the alternator belts (cross posted from Delica.ca)

Steps 1-2 are optional, but advised if this is your first time. Once you've got the hang of it you'll find you can loosen the clamp bolt (2) from underneath.
1) lift up the passenger seat
2) remove the fan cowling (both halves)

3) jack up the front right corner of the vehicle. It is not necessary to raise the wheel off the ground. Lifting the body just gives you a little more elbow room.
4) remove the brush protection pan underneath the engine (2x 14mm bolts and 4x 12mm bolts)
5) loosen the alternator mounting bolt from underneath (1) the vehicle using a 12mm socket and wrench
6) loosen the clamp bolt (2) that locks the alternator in position. From above is easier (after you've removed the fan cowling) but from below is possible.

Here's an impossibly good view of what you're trying to adjust. You'll never see this, you'll be doing it all by feel:

7) Use a ratcheting box wrench on the tension bolt (3), or alternatively remove the driver's side front wheel, lift the rubber flap in the wheel well, and if you're lucky the tension bolt head (3) will be reachable using a socket and long extension. You may need a universal joint on the socket.

8) A correctly tensioned alternator belt will deflect 10mm when pushed with a force of 10kg/22lb, pressed in the middle of the lowest run. If you press with your thumb about as hard as you comfortably can, that's around 10kg. If you're unsure, use a bathroom scale to calibrate your thumb.

9) go back out the way you came in, tightening everything you loosened, and putting back everything you took off.

If the belts continue to squeak when correctly tensioned you'll need to replace the belts. Don't overtighten them in an effort to stop the squeaking- the water pump bearing will fail. Trust me, I know.

 

[Growlerbearnz]

New belts that squeal might be the wrong shape.

TL;DR: Genuine Mitsubishi alternator belts (a matched pair is part number MD313660) are unusually shallow and appear to fit in the pulleys better, making them squeak less than some aftermarket belts.

OEM Mitsubishi belts are only 6.6mm deep.

Over time these belts wear a step into the pulleys. If you replace these belts with deeper belts like this...

...you'll see that the lower 2-3mm of the deeper belt rides on the un-worn part of the pulley, while the rest of the belt rides on the worn part. This doesn't work. The lower 2-3mm of belt will try to take most of the load (because the un-worn part of the pulley is tighter) while the rest of the belt is kind of floating.

Here's those ribbed belts after 5000km on worn pulleys: the lowest, ribbed part shows a 3.5mm strip of extra wear, you can see the step just below the ribs.

The correct solution is to replace all the pulleys, but it's easier to just use genuine Mitsubishi belts.

 

[Growlerbearnz]

Still squealing after replacing the belts?

Water Pump:
Check for coolant leaking from the water pump. Remove the belts and check that the water pump turns freely.

Alternator misaligned:

TieMyShoe wrote:The lower alternator mount bracket is part of the front cover/oil pump and made of aluminium with no bushings in the hole. Over time the bracket has worn to an oval shape in the front allowing the alternator to sit at a slight angle. This tiny angle caused a constant squeak.

Loosen the alternator mounting bolts and belts and then try to twist the alternator on its bracket. Any sideways movement here means the hole in the bracket has worn oval.

The bracket hole can be drilled out to 10mm (access is tight, you might need to remove the radiator to get a straight shot at the bracket). Once you've drilled it out either fit sleeves to make the holes 8mm again (I like the steel-backed teflon lined bushes) or drill out the alternator flanges and use a 10mm bolt.

The bracket is actually part of the oil pump: if your bracket is so worn that it can't be drilled out (or you screw up the drilling!) replacing the bracket requires pulling the oil pan and replacing the whole oil pump.

Crankshaft:
Sometimes the outer ring of the crankshaft pulley becomes separated from the inner piece. With the engine running check that the crankshaft pulley turns smoothly and doesn't appear to wobble.

Not actually the alternator belts squealing:
Remove the power steering belt and run the engine. Still squealing? Try the AC belt.