Squeaky alternator belts: an investigation.

Post by **Growlerbearnz** » Mon Dec 05, 2016 3:52 am

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.
Also:

TieMyShoe wrote:The lower alternator mount is part of the front cover and made of aluminum with no bushings in the hole. Over time the cover 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.

A bit of background: 35,000km ago I fitted a new water pump and drive belts. The belts always squeaked a bit, even when tensioned to the factory specs (13-16mm deflection at 10kg force), so I just tightened them until the squeaking stopped. Unsurprisingly the water pump bearings failed after 30,000km. New water pump fitted 5000km ago with new belts, but this time I left the tension at factory spec and just lived with the chirping when cold- until now, when I decided to figure out what was going on.

I bought a new set of genuine Mitsubishi belts (Part number MD313660 is a matched pair) and started experimenting.

Method: Tension belts to 13mm deflection on the longest section when applying 10kg force. Charge battery until charger says it’s finished. Turn on headlamps to bright, front and rear fans on full, aircon off. Idle warm engine at 750rpm.

Gates XL 11A1065 belts with 5000km use: light chirping noise at 13mm deflection. Chirping goes away when tensioned to 8mm deflection (which is too tight). Constant chirping at 16mm deflection.

Mitsubishi MD313660: Silent at 13mm deflection. Silent at 16mm deflection. Slight squeak at 20mm deflection. (Though these are brand new belts, so I'd expect them to be more grippy- we’ll see how they fare once they have 5000km of wear on them.)

Now here's the odd thing:

The Mitsubishi belts are only 6.6mm deep…

: MitsuBelts.JPG (42.3 KiB) Viewed 6422 times

where the Gates belts are nearly 9mm.

: Gatesbelts.JPG (45.42 KiB) Viewed 6422 times

The lowest, ribbed part of the Gates belts shows a 3.5mm strip of extra wear, which is unusual. I checked a bunch of other belts on other vehicles, and they were all worn evenly.

: WornBelts.JPG (37.91 KiB) Viewed 6422 times

I suspect one or more of the pulleys has grooves that aren’t deep enough or shaped correctly for the deeper Gates belts, and they’re grabbing on the wrong part of the belt, creating friction and slippage. Or (more likely) the water pump pulley has just worn to suit the original style belt, and the deeper belt is grabbing the unworn part of the pulley (I suspect the water pump pulley because the crank and alternator pulleys are new, and they look fine. The water pump pulley is more difficult to inspect).

I’ll recommend buying genuine Mitsubishi alternator belts from now on. MD313660 is a set of two belts with sequential serial numbers, and only cost me NZ$20 (which is cheaper than two aftermarket belts).

Post by **thelazygreenfox** » Mon Dec 05, 2016 11:32 am

well done!
MD

lrp374 · Post by **lrp374** » Thu Dec 08, 2016 3:10 pm

Thanks for the info Growler. I have been going nuts with the belts I now have. They look like great super heavy duty type made by Mitsuboshi but they squeak, flap alternator to crank and now they've started to come apart after only 15000 km. I was going to buy the Gates units to replace them but after I see what yours are doing I'm going to make sure they are new Mitsubishi for sure. I think the ones I had before this were Dayco and they lasted about 60000 before one of them came apart. How come this application is so hard on belts?

Post by **Growlerbearnz** » Fri Dec 09, 2016 1:34 pm

Mine don't wear out as such, they just make noise when they're not genuine Mitsubishi ones.

The flapping on the lower run suggests not enough tension. I've just measured mine- I get 10mm deflection on the lowest run (which is easier to get to without removing the engine cover).

Maybe one of your pulleys is in worse shape than mine?

TieMyShoe · Post by **TieMyShoe** » Mon Dec 12, 2016 4:03 pm

I fought with squeaking belts for the longest time, tried different belts, more tension, silicone spray.. you name it. squeak always came back. finally figured out what was wrong. The alt mount is part of the front cover and made of aluminum with no bushings in the hole. Over time the cover has worn to an oval shape in the front allowing the alt to sit a slight angle. this tiny angle caused the constant squeak. putting a pry bar under the alt pushing back to its correct spot worked for a bit but the alt would always work its way back. I ended up removing the front cover, welding the hole up and drilling a new hole with a mill... squeak has not returned, running Dayco belts.

Post by **Growlerbearnz** » Tue Dec 13, 2016 1:42 pm

TieMyShoe wrote:The lower alternator mount is part of the front cover and made of aluminum with no bushings in the hole. Over time the cover has worn to an oval shape in the front allowing the alternator to sit a slight angle.

Damn, I had forgotten that! Mine too was worn oval when I got the van. I discovered it when fitting a larger 90A alternator which used a 10mm bolt instead of the original 8mm, so I drilled the mounting bracket hole larger to suit the new alternator- removing the ovality in the process. The belts used to squeak something terrible, and the noise got better when I fitted the new alternator, but I had also fitted new belts at the time so I figured the new belts and alternator pulley had fixed it. Maybe it was also due to the alternator angle?

I wonder how common the flogged out mount hole is?

sealica · Post by **sealica** » Fri Dec 16, 2016 5:55 pm

If I'm following the conversation correctly we are perhaps talking of the "oil pump housing" which the alternator is bolted to?

I've had a weird month. After replacing the windshield wiper linkage, suddenly my van was making a really weird noise (completely not related) - especially at low RPM idle, but also on the highway. I was taking it to a mechanic for a ball joint anyhow and when we looked at it on the hoist the alternator was rattling around on account of a loose bolt (the one through the oil pump housing). The AC belt and pulley had also started to fall apart.

In any case looking up at the bottom of the alternator the lower bolt is definitely askew ... not completely diagonal, but definitely off centre. It's kind of a difficult repair to swallow because replacing the oil pump housing will require taking apart the timing cover, draining oil, and working near the water pump and balancer belts. I had considered trying it myself, but the mechanic figures it will take 6 - 8 hours which is a long time to work in the frosty driveway.

I had considered letting it go (bolt is tight, but who knows when it could fail) until warmer days, but I kind of want to use the van sooner - and we don't drive around town (where I wouldn't be as worried). But going down 100km of bumpy gravel roads and possible ice and etc ... just asking for the alternator to brake loose and the water pump to cease fuctioning ... cue tow truck to middle of no where ... which is much more expensive than say just getting it fixed. But hard to swallow since the timing belt was replaced by a shop 6 months ago by previous owner.

There was also a new alternator put in 3 months ago (still previous owner), but perhaps it wasn't the shops fault and these brackets just get stressed over time?

Eek

Post by **Growlerbearnz** » Sat Dec 17, 2016 3:28 am

If you remove the radiator you can get a drill in there to drill out that hole to a larger size, then fit a larger bolt (or some kind of bushing). Might save having to replace the entire oil pump?

Captain America · Post by **Captain America** » Wed Jan 04, 2017 7:51 am

To add to the info pool. Over the 2016 Thanksgiving holiday I had my timing belts and all other belts changed. Used dayco for the tensioner/timing belt and Gates for all others. I have since put on close to 1500 miles and I have a persistent squeal during start up and regular operation. So much so that I put the vehicle in neutral a stoplights here in NYC. That is a lot of stop lights and a lot of neutral.The squealing subsides when I do this. My next step is to order original Mitsubishi belts and replace the Gates aftermarket ones. Once done I'll report my findings.

Regards

Post by **Morganizer** » Sat Jan 07, 2017 6:49 pm

My L300 has a squeal at startup in cold weather only. Persists for the first 2 minutes, then fine. Was worse when I bought the van, and I tensioned the belts (see my lengthy post for procedure: http://www.delica.ca/forum/viewtopic.ph ... 881#p90881 ) and applied some CDN Tire belt dressing, which improved it slightly. I can see one of the belts is glazed from being loose (previous owner never adjusted it) and I've assumed the squeal will stop when I get around to replacing the matched pair of belts.

Captain America · Post by **Captain America** » Sun Jan 08, 2017 11:46 am

Morgan,
For the reference point are the belts giving you the squeal aftermarket or Mitsubishi?