W204 C220 CDI rough rattle when idling at 750rpm.

[RRV8]

Hi guys, I have this 2009 c220 cdi. I am very happy with this car. Plenty power and very good fuel consumption is very good. In recent months though while the engine is idling at 750rpm there is a load roughness or rattling coming from under the bonnet. When I press the clutch the idling goes up to 900 rpm and the rattling or roughness dissappears. Also when the auxillary belt is removerd, the idling is very smooth. As soon as the auxillary belt is put back on the roughness comes back into play again.The auxillary belt and pulleys and water pump were replaced, but the roughness is still there. A belt was fitted with the AC unit removed and still the roughness is there. The alternator bearings seems fine. I am not sure if the steering pump ok or not. I noticed that when i turn the steering pump pulley by hand forward and backwards there is play on the gears inside thd pump.
Could anybody shine some light on wht the roughness could be. 135,000 miles on the clock.

 

[alecmascot]

Alternator pulley clutch ?

 

[rusky]

Do these have a dual mass flywheel? If so, it sounds like it's failing.

 

[RRV8]

Alternator pulley clutch ?

No such thing as a alternator clutch pulley on a C220 Cdi. There is simply a alternator with a pulley. There is no play what so ever in the bearings of the alternator. I do not suspect the alternator. Thanks.

 

[RRV8]

Do these have a dual mass flywheel? If so, it sounds like it's failing.

No it's not the flywheel failing. Thanks anyway. The noise is out at the front of the engine.

 

[rusky]

I was kind of grasping at straws when you said the noise goes when the aux belt is removed but you never know on cars, some seemingly unrelated items have odd effects!

 

[RRV8]

You are right no doubt. I was sure it was the water pump. But nope it ain't. It's is not a metallic grinding or worn bearing sound. I do notice that the belt tensioner is erratic when the annoying noise is present. When I spray belt grip spray on the belt the noise disappears for 2 mins but comes back again. I have checked and cleaned the pulleys them selves. Even if I sprinkle water on the belt the noise disappears for 2 mins. Sounds so simple to fix but I cannot. I have changed the aux belt to a shorter one to by pass the AC pump. I still get the same annoying rattling sound

 

[RRV8]

You are right no doubt. I was sure it was the water pump. But nope it ain't. It's is not a metallic grinding or worn bearing sound. I do notice that the belt tensioner is erratic when the annoying noise is present. When I spray belt grip spray on the belt the noise disappears for 2 mins but comes back again. I have checked and cleaned the pulleys them selves. Even if I sprinkle water on the belt the noise disappears for 2 mins. Sounds so simple to fix but I cannot. I have changed the aux belt to a shorter one to by pass the AC pump. I still get the same annoying rattling sound

Also when I do manage momentarily stop the annoying rattling sound the belt tensioner remains very steady with very little movement.

 

[rusky]

It can only be the tensioner really. Is there an idler pulley on that engine?

 

[Trickythemerc]

No such thing as a alternator clutch pulley on a C220 Cdi. There is simply a alternator with a pulley. There is no play what so ever in the bearings of the alternator. I do not suspect the alternator. Thanks.

I beg to differ about the alternator clutch pulley on a 220 CDI........... I have just changed mine, SKF part number VKM03820

 

[rusky]

Is the short belt new or used?

 

[RRV8]

Is the short belt new or used?

New belt

 

[RRV8]

I beg to differ about the alternator clutch pulley on a 220 CDI........... I have just changed mine, SKF part number VKM03820

Thanks I will keep it in mind, I would like to exchange the alternator with another one just to see if there is a difference.

 

[Trickythemerc]

There is always a chance that the alternator has been changed at some point to a non clutched one. There should be a plastic cap on the front of the pulley covering the bore of the rotor shaft. this have splines in the pulley and female torx in the shaft.

 

[RRV8]

There is a plastic cover over the center of the pulley. I presume this is simply a pulley which slides off the spline shaft after the bolt is removed. Is it this pulley that you got replaced and why?

 

[rusky]

Do any pulleys have even the slightest movement in any direction with the belt removed?

 

[Trickythemerc]

The shaft is not splined it is threaded and there is no bolt. The pulley uses sprag clutches to allow the rotor to free wheel under deceleration as the engine RPM drop. Test the pulley to see if if it will rotate freely in one direction and lock up in the opposite rotation, there should be no crunching in the pulley bearings. Not an expensive thing to change £25.00 ish But you will need special tooling to change it.

 

[RRV8]

The shaft is not splined it is threaded and there is no bolt. The pulley uses sprag clutches to allow the rotor to free wheel under deceleration as the engine RPM drop. Test the pulley to see if if it will rotate freely in one direction and lock up in the opposite rotation, there should be no crunching in the pulley bearings. Not an expensive thing to change £25.00 ish But you will need special tooling to change it.

Thanks very much for that info. I will have to check my pulley again later today. I am certain it is not what u described above. Hopefully mine is seized and like you said need a simple replacement. I will let you know later on, thanks again.

 

[RRV8]

Do any pulleys have even the slightest movement in any direction with the belt removed?

0.5mm or less

 

[RRV8]

The shaft is not splined it is threaded and there is no bolt. The pulley uses sprag clutches to allow the rotor to free wheel under deceleration as the engine RPM drop. Test the pulley to see if if it will rotate freely in one direction and lock up in the opposite rotation, there should be no crunching in the pulley bearings. Not an expensive thing to change £25.00 ish But you will need special tooling to change it.

The shaft is not splined it is threaded and there is no bolt. The pulley uses sprag clutches to allow the rotor to free wheel under deceleration as the engine RPM drop. Test the pulley to see if if it will rotate freely in one direction and lock up in the opposite rotation, there should be no crunching in the pulley bearings. Not an expensive thing to change £25.00 ish But you will need special tooling to change it.

You are spot on Trickythemerc. My clutch on my alternator is seized. I never new the even existed. I need to replace in and got to get the special tool for the job. Thanks everybody for your input. I will let ye know when I have a new one fitted.