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Mercedes Model: 1978, 250, 6Cyl, Gasoline: Chasis: 123026-20-044500, Engine: 123920-20-021475
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Discussion Starter #1
W221-S500-5.5L-RHD

I am told that the noises are caused by worn out bearings.
The adjuster and another one is apparently an easy fix, however the Alternator and Water Pump are difficult and length job. In one of the cases I am told one can’t just replace the bearing.

1. pls advice if the info is correct. 2. Which ones are required to be changed and at what period
3. Which brand other than OEM will be good to use.
 

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Outstanding Contributor W221 Moderator
2010 E350 P1/P2, 2008 S550 Designo, 2002 ML320
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1,910 Posts
Noises can indeed come from worn bearings or the unit being powered by the pulley attached to the bearing. I have seen alternator bearings replaced, but water pumps almost never, usually replace the whole unit. The first thing I would do is remove the poly v-belt and rotate each pulley by hand. You should be able to tell which one is the source of the noise.

Also as for change interval it really just depends on the quality of the part and environmental conditions. Lots of salt, road chemicals for snow/ice, etc. can cause them to wear prematurely. I would expect a water pump to last 100k miles but not much more based on experience with M112, M113, M272 and M273 engines.
 

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W164 GL450, W221 S550, R230 SL600TT, R170 SLK230, W140 S500, More
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I find it hard to believe that every pulley and every bearing in there is bad all at once. I would remove the belt and check the pulleys and bearings. I bet that just your belt tensioner and idler pulley's bearings might be bad, but I doubt the others are. Like DLA said,
remove the poly v-belt and rotate each pulley by hand. Wiggle sideways, ...You should be able to tell which one is the source of the noise.
 

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W164 GL450, W221 S550, R230 SL600TT, R170 SLK230, W140 S500, More
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For brands to buy, I would look at Rockauto dot com and FCPeuro and if I recall, everything FCP sells they guarantee for life. Personally I look for german parts.
 

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Mercedes Model: 1978, 250, 6Cyl, Gasoline: Chasis: 123026-20-044500, Engine: 123920-20-021475
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41 Posts
Discussion Starter #5
I find it hard to believe that every pulley and every bearing in there is bad all at once. I would remove the belt and check the pulleys and bearings. I bet that just your belt tensioner and idler pulley's bearings might be bad, but I doubt the others are. Like DLA said,
remove the poly v-belt and rotate each pulley by hand. Wiggle sideways, ...You should be able to tell which one is the source of the noise.
thanks, wiggling I assume will reveal play due to wear? This would mean replace the pulley/bearing
 

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W164 GL450, W221 S550, R230 SL600TT, R170 SLK230, W140 S500, More
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Yes if it feels like gravel or feels loose then the bearing would be bad. Most of the time it's the idler pulley and the belt tensioner along with a new belt, that renews and often that's all that's required. My mechanic has a stethoscope with a stick on it, he holds up to the pulleys while the engine is running to hear the scratchy sounds worn bearings at the front of the engine, obviously when it is running this can be dangerous if you're not careful where you place it, if it gets caught in the belt or fan, etc., OH DARN, that reminds me, my R170 SLK needs an ideler pulley, I'd almost forgotten.... Ok in the spring I'll get one.
 
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