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Old 26-10-2019, 21:51   #1
The Rock
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Aux belt tensioner help?

I went to change my aux belt as it was looking a bit worn and starting to squeal when I realised that the tensioner was knackered and jumping all over the place on idle. Also the metal lug hole used to take the tension off the belt broke as I tried to remove the belt.
A few searches and phone calls later I was told by some folks that its the same aux belt tensioner for all evos 4-9, and by some others that there are specific parts for 456 and 789. Official parts were md355488 for 456 and md149179 for 789.

After a bit of research, I went for an aftermarket one that was listed for an EVO 7 presuming it would fit my evo 6 TME (if they were all the same). Here it is also listed for many other Mitsubishi's.
https://www.ebay.co.uk/itm/Aux-Belt-...5964%7Ciid%3A1

The good news is that it fit. At first one of the bolts holes seemed a bit off, but it has gone on fine. On idle it does not move at all (no jumping) and the squeal has gone.
The problem is it very tight (like a guitar string), and when I start the engine you can really feel the whole car vibrate/ shudder (which has never been the case before). Can a tensioner be too tight? Anyone else know if all the tensioners are the same for evo 4-9? Could the belt tension cause other problems or in anyway be the reason why the car now vibrates on start up?

You may be asking why I did not just go for the OME part ? Well £80 is quite a big difference in price and my car is made up of mostly aftermarket parts which work just as well if not better than the originals and also cost alot less.

Thanks for anyone who has time to comment or reply..
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Old 27-10-2019, 10:20   #2
swinks
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Well, I don't think that tensioner itself is your problem. Myself, I have changed one for aftermarket one, 3 years and good as new.
I rather think that symptoms you described are from failing crank pulley. It's 2 parts pulley with galvanized rubber to deal with harmonic vibrations of the engine. With time rubber perishes and pulley falls apart. Because it drives aux belt, then early signs are like shredding belt, squeaks, vibrations, belt falling off etc. So having loose aux belt might mask symptoms of crank pulley off balance, whilst proper tension, you feel it right away.
That's just my guess, worth check IHMO, as I can't believe that tight belt will give you set of vibrations. Off balance pulleys... yes.
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Evo 8 FQ300: 325 WHP and 375 LbFt torque at 1.6 bar
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Old 27-10-2019, 13:16   #3
The Rock
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Quote:
Originally Posted by swinks View Post
Well, I don't think that tensioner itself is your problem. Myself, I have changed one for aftermarket one, 3 years and good as new.
I rather think that symptoms you described are from failing crank pulley. It's 2 parts pulley with galvanized rubber to deal with harmonic vibrations of the engine. With time rubber perishes and pulley falls apart. Because it drives aux belt, then early signs are like shredding belt, squeaks, vibrations, belt falling off etc. So having loose aux belt might mask symptoms of crank pulley off balance, whilst proper tension, you feel it right away.
That's just my guess, worth check IHMO, as I can't believe that tight belt will give you set of vibrations. Off balance pulleys... yes.
Thanks, I had the crank pulley fail a while back now. Half of it fell off while driving and I was left with a loose belt. I got hold off an Evo 8 crank pulley and put that on and have not had a problem since as they are alot stronger.

The car has been running great for years, just had a series of problems recently and am starting to think its time to book it in at ND. A new noise has also appeared that sounds a bit clunky from the belt area. Its hard to pinpoint and can mostly be heard from inside the car, hoping its not noise from the balance shaft area as I have not had that deleted yet.

Overall the new vibration on startup, the clunky noise along with some brake problems( noise on turning left from drivers side after fitting new pads) and now the expansion bottle filling up when hot and disappearing completely when cold (which it has never done in 15 years of owning the car) I am starting to think its time to let the professionals take over.. Its not overheated yet, but the bottom radiator hose is cold, and the top of the rad feels boiling (thermostat possible??). Strange all these problems have come at the same time lol.. Perhaps its the water pump?

Thanks for your help
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