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changing fan belts on Merc. OM422 motor

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changing fan belts on Merc. OM422 motor

Postby FrednKathy » Sat Sep 05, 2015 11:43 pm

Hey guys, new to this forum, tho' we are independent, well travelled retirees, enjoying Oz in our Merc. 0303 fully self contained motorhome.... I want to replace all the double fan belts on the 422 V8 motor, and note the compressor belts look to be pneumatically tensioned, and the belts to the fan seem to have a pulley that may also be a tensioner as well...is there a sequence or any special precautions I need to know...how do I relieve the air pressure on the the compressor tension arm...your nformed advice sought and appreciated....regards, Fred n Kathy
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Re: changing fan belts on Merc. OM422 motor

Postby Guy_Arab » Sun Sep 06, 2015 10:06 am

FrednKathy wrote:Hey guys, new to this forum, tho' we are independent, well travelled retirees, enjoying Oz in our Merc. 0303 fully self contained motorhome.... I want to replace all the double fan belts on the 422 V8 motor, and note the compressor belts look to be pneumatically tensioned, and the belts to the fan seem to have a pulley that may also be a tensioner as well...is there a sequence or any special precautions I need to know...how do I relieve the air pressure on the the compressor tension arm...your nformed advice sought and appreciated....regards, Fred n Kathy

I will email you a diagram
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Re: changing fan belts on Merc. OM422 motor

Postby FrednKathy » Wed Sep 09, 2015 1:00 pm

Thanks to Guy Arabs information and advice, I was able to overcome my problem with the fan belt pulley tensioner...immediately behind the fan pulley tensioner is a clamp nut, which has to be slackened first..this pulley is offset, so when turned, will either loosen or tighten the twin belts...the pulley shaft can then be moved vertically up or down once the two retaining bolts are loosened...this allows the fan belts to be removed...However, to reinstall and tension the belts is a little different....with the belts on the pulleys, and the clamp still slackened, raise the tensioner pulley upwards by the adjusting nut until the belts to the CRANKSHAFT are tensioned enough...DO NOT OVER TIGHTEN BELTS...the belts to the FAN, if still too loose, can be tensioned more by rotating the tensioner pulley one way or the other, due to it being off centred...tighted all bolts, not forgetting the clamp bolt behind the pulley, and Voila...I'm told this setup is common on most early Mercedes engines, but also on other European motors as well, and if the above procedure is not followed, the tensioner pulley can be damaged due to strain.This is a long winded blog, but may be of use to others at some time perhaps... P.S..I'm wanting to buy a workshop manual for my Mercedes OM422.1.1.1 V8 diesel on a 1625 chassis..Avagoday all...Fred n Kathy
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Re: changing fan belts on Merc. OM422 motor

Postby Camaro » Sun Sep 17, 2017 11:13 pm

Hello from Latvia. Sorry for my bad English.
We have old Claas Commandor 116CS combine with OM422 engine. Problem is fan belt tensioner bearings are breaking all the time, like 2 hours and they are done. Can`t figure out what is wrong. Also fan belts are getting more tense as they heat up, basically you have to readjust them half an hour or so. Just today belts were adjusted like 3 times (loosened, so they won`t snap), but still tensioner bearings broke and we have to change them again. I have theory that SKF bearing party which we use is of poor quality, or maybe fan bearing is not good and fan pulley is like in an angle against tensioner pulley so belt is kinda of climbing up fan pulley and getting more tense and in the end tensioner bearings give up as they are smaller than fan bearing.
What`s your thoughts on this? Maybe some of you have had similiar problems with other engines?
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Re: changing fan belts on Merc. OM422 motor

Postby boronia » Tue Sep 19, 2017 4:02 pm

I worked in a fleet of Merc buses many years ago (O302 and O303).

The main problems I can recall with fan belts was pulleys out of alignment with each other, and wear on the pulley faces resulting in the belts not seating correctly.
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Re: changing fan belts on Merc. OM422 motor

Postby Camaro » Sat Sep 23, 2017 6:38 am

Well, it seems that it was alignment issue. Tensioner bracket axle was loose, so pulley was a bit out of place. Still strange that belts were getting tighter and tighter as they got hotter.
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Re: changing fan belts on Merc. OM422 motor

Postby Camaro » Thu Sep 28, 2017 6:14 am

Update. Well, i guess we were morons and didn`t knew how to properly tighten belts. Friend come and adjusted fan belts really tight. You could pull them just by 5mm to each side. And it seems that problem is gone for now. There is still minor movement in fan bearings, unforutnately we can`t them as they have weird construction. Axle is part of bearing with grooves for bearing balls, so can`t really change them, and asking around it seems to impossible to get new fan bracket for such old motor even from local Mercedes dealer. :(
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