Do you really need both alternator belts?

Does your Mitsubishi L300 make a strange noise? Need wheel alignment specs?
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murdermitten
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Do you really need both alternator belts?

Post by murdermitten » Mon Sep 17, 2018 11:07 pm

Hello again-

I'm very, very tired of adjusting my alternator belts. I can go quite a while with them being nice and quiet, but I guarantee I'll have to tighten them at least once or twice a month. I'm running MD313660 belts.

I've also noticed one of them seems to wear out pre-maturely, the one closer to the fan, further from the block. I've read on other posts that perhaps the alternator mounting bolt (the lowest one for pivoting the alternator- you loosen it to adjust belt tension) is out of round causing irregular wear, but it seems to tension up nicely and there is no play.

I also seem to run out of tensioning "room" as the adjustment screw on top (the one whos head faces towards the right front tire) is nearly tight against the square block that tensions it in place.

So, I'm wondering if this forward-most belt is the culprit, can I cut it off and run one belt? I realize this isn't the true solution to my problem, but does anyone do this?

Happy to walk through all the issues, but this one came to mind as an easy fix and I thought I'd play devil's advocate and ask.

I'd love to solve this annoying alternator issue once and for all.

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Growlerbearnz
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Do you really need both alternator belts?

Post by Growlerbearnz » Tue Sep 18, 2018 3:35 am

Only one way to find out! I reckon the two belts are there because after using the glow plugs, the alternator puts a heck of a load on the belts, and one belt would likely wear out too quickly for Mitsubishi's liking (IE while the van was still in warranty).

If you're using a matched pair of genuine belts, the adjuster should be about halfway along its adjustment. That it's almost at the end of the adjustment says that something's in the wrong place. The usual culprit is the lower mounting bolt as you've said (or, more correctly, the pivot point on the engine) going out of round and letting the alternator sit on an odd angle. Pull the bolt out and swing the alternator away, and check the pivot points on the engine. You'll have seen in other posts how it's possible (but irritating) to drill them out and fit a larger bolt.

The other thing to check is the fan pulley. Unlike the machined pulleys on the alternator and crankshaft, the fan pulley is pressed steel, and seems to wear more quickly. Check it for wear where the belt runs, the belt will have worn a ridge into the pulley. If the belts have been overtightened they might have distorted the pulley as well, opened out the V's, but I'm speculating there.
Nothing says "poor workmanship" more than wrinkles in the duct tape.

murdermitten
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Do you really need both alternator belts?

Post by murdermitten » Tue Sep 18, 2018 9:51 am

Thanks once again Growler Bear!

I ordered a replacement fan pulley a while back as I thought it might be the culprit, but have yet to install it- maybe I do that if it's not too much trouble.

I agree I think there's something out of alignment, either the pivot (long bar to which the adjustment screw/block slides along) or the lower mounting bolt.

Last night, in my frustration I thought to loosen the pivot bolt in an effort to get it to angle slightly down more in order to give me more tensioning ability...it didn't seem very effective, was this a bad idea? To make it clearer, I had all of these bolts in various states of looseness in an effort to get an acceptable amount of tension:

-Pivot bolt where it bolts to the front of the engine (just a little loose allowing the bracket itself to droop a little)
-lower mounting bolt (very loose)
-"block" bolt that tensions the adjuster screw to the pivot bracket
-adjustment screw (which I continually backed out in an effort to let the alternator swing further away, thus tightening the belts(?) I tried to get it about halfway but it gets a little difficult to keep it in it's bracket at the end of the pivot.

My next thoughts tonight are to pull the fan and fan shrouds loosen everything once again and see if I can't get them truly tight. I may replace the pulley depending on how inspired I am but I'll be sure to take plenty of pics while down there.

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Growlerbearnz
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Do you really need both alternator belts?

Post by Growlerbearnz » Tue Sep 18, 2018 2:20 pm

If you have a new pulley sitting there, definitely replace it. It's very easy to replace- undo the 4 bolts that hold the fan clutch in place, and the pulley will just fall off. Removing the fan and shrouds is the trickiest part!
Nothing says "poor workmanship" more than wrinkles in the duct tape.

murdermitten
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Do you really need both alternator belts?

Post by murdermitten » Tue Sep 18, 2018 9:31 pm

Okay spent another few hours poking around...I did end up cutting one of the belts off (it was in terrible shape), but in the end will need to take everything off and re-install new belts. It's maddening how shredded these belts are, considering all of them were replaced at the same time less than 3 months ago! I assume that even if it only recently started squealing that it's been slipping and burning up the belts for some time.
ALTBELT 1.pdf
(110.77 KiB) Downloaded 64 times
ALTBELT 2.pdf
(108.72 KiB) Downloaded 57 times
Also, something is very off since the tension setting screw is maxed out...I'll start with putting new belts and a new center pulley in and see where that gets me.

helibrian
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Do you really need both alternator belts?

Post by helibrian » Wed Sep 19, 2018 1:08 am

You should definitely keep both belts especially if you are having problems with one braking. There’s an oil pump on the back of the alternator so if it stops spinning the oil stops flowing.

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Growlerbearnz
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Do you really need both alternator belts?

Post by Growlerbearnz » Wed Sep 19, 2018 2:51 pm

There's something seriously wrong there. Both belts should wear at the same rate, and even a very old, worn out single belt shouldn't be worn down to that thin.

Look for damage to the pulleys, the fan pulley could be bent relatively easily. Alignment of the alternator and the other pulleys might be off as well, depending on how sloppy the lower pivot bolt is.
helibrian wrote:There’s an oil pump on the back of the alternator so if it stops spinning the oil stops flowing.
Worse than that, it's the vacuum pump for the power brakes. (The oil is there to help seal the vacuum pump). If the alternator stops you get one or two brake applications before the pedal gets *really* heavy.
Nothing says "poor workmanship" more than wrinkles in the duct tape.

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JMK
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Do you really need both alternator belts?

Post by JMK » Thu Sep 20, 2018 6:35 pm

I recall years ago there was extensive discussion about this topic in the forum.

The result was, when I bought new belts, I was obsessive/compulsive about matching the numbers on the belts to make sure they were brothers cut from the same source stock. The thinking was that two belts that were not cut side by side could easily have perhaps as much as a millimeter of extra diameter, which would make accurate tensioning problematic. I would hope that if one belt is slightly smaller, it would stretch out until the pressure on the pulley equalized, but I can appreciate why this might be of concern when sourcing new belts.

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Growlerbearnz
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Do you really need both alternator belts?

Post by Growlerbearnz » Fri Sep 21, 2018 12:04 am

That's the nice thing about using genuine MD313660- that's a matched pair of belts. :-)
Nothing says "poor workmanship" more than wrinkles in the duct tape.

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Do you really need both alternator belts?

Post by nenw » Mon Dec 31, 2018 6:14 pm

hey crew, I am dealing with this same issue right now. My alternator adjuster is topped out with only maybe 20 miles on the new belts and there is a ton of slack in them.

2 thoughts on this: My alternator pivot bolt is frozen in place. I have been able to get the alt to pivot I just cannot remove the bolt at all. I thought maybe it wasn't sitting flush or tight, but it is both flush and tight. I spent way too much time with a little torch and some penetrating fluid today, which I also did when I was working on the timing, a few weeks ago but no luck. I think I may need a shop to remove if necessary.

Any chance it might be the harmonic balancer that is causing this? 30 year old van, all other belts are good, the van is a little shaky when starting and cold and it's blowing through 2 sets of belts. Any way to test this theory?

I was thinking of just replacing the pulley on the fan and the harmonic balancer. Thoughts?

dedi
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Do you really need both alternator belts?

Post by dedi » Thu Feb 28, 2019 11:11 am

It was definitly the fan pulley on my 4D56, struggled for years with matched pais of belts, OEM Mitsubishi ones, Gates high quality, nothing helped. Pulley is only pressed steel, a machined one would be way better as said before. Finally replaced the fan pulley, it was not only worn (after 350.000 km) it was sqeezed open by rising the tension I finally put on the belts to get rid of that squirrel noise. Once you've got the pulley out you will be able to tell by measurement, comparison with the new one or just by pushing in 2 new belts...

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