W203 rattle at tickover

[diarmaid]

Has anyone got the definite answer to the rattle at tickover on a w203.
I bought my w203 with 55k miles,I have replaced the belt and tensioner twice
in 40 k miles it is now slapping again.Do I replace belt and tensioner again ?
other posts suggest alternator pulley ,engine mounts et cetera.
I am grateful for any help.
Diarmaid

 

[wireman]

Take off the belt and run the engine for a few moments, whilst its running listen for the rattle and if its still there it is nothing to do with the belt or pulleys.
Feel the pulleys whilst the belt is of for looseness, bearing wear and slap etc.
Did you replace the belt tensioner damper/shock absorber? if not this may be your trouble.

 

[diarmaid]

Should have mentioned my car is an auto 2002 with 95k miles
Thanks,
Diarmaid

 

[Ellsy Tanners]

Petrol or diesel?

 

[diarmaid]

Diesel 220 cdi

 

[Ellsy Tanners]

The most common cause of belt slapping on a cdi 220 that i have come across, is the alternator free wheel clutch.

Have a look at the alternator pulley and see if it is hollow ( none free wheel clutch ) or has a black plastic cover and the pulley is solid ( contains a free wheel clutch. )

 

[diarmaid]

yes it has a black plastic cover.

 

[ernieh]

Free Wheel Clutches

Hi All,
Sorry to go off thread.....but why do modern cars have free wheel clutches on their alternators. I would have thought the scope for energy savings would have been limited using these devices...or is there something I'm missing?

Thanks for any information.

Ernie

 

[Xtractorfan]

Free wheel clutches..Practically all new cars are now using this or similar methods to save fuel & increase power , basically batteries dont need to be charged ALL the time the engie is running. so when you accelerate the car needs as much power as it can get so the alternator..a big power user.. runs free and doesnt charge the battery, then when you release the throttle ..on the overrun..the alternator starts charging..

 

[ernieh]

Alternator Clutches / freewheels

Thanks, Xtraxtorfan, I knew somebody would be able to enlighten me.....the first one of these I came across was recently when a friend's Renault Clio came to a halt making the most horrific noise. On inspection, the alternator clutch had disintegrated and, I discovered, if the 7 year old car had had a complete service history, the job would have been done under Renault's goodwill scheme. As it was, the part was replaceable albeit at a cost of £140 including labour and a new drive belt.

Regards,


Ernie

 

[minijohn]

Free wheel clutches..Practically all new cars are now using this or similar methods to save fuel & increase power , basically batteries dont need to be charged ALL the time the engie is running. so when you accelerate the car needs as much power as it can get so the alternator..a big power user.. runs free and doesnt charge the battery, then when you release the throttle ..on the overrun..the alternator starts charging..

That's wrong.
The freewheel clutch works the other way round - the alternator CANNOT run slower than the engine.
The freewheel clutch allows the alternator to slow down gradually when the engine is stopped, so not putting a strain on the drivebelt
John

 

[diarmaid]

Thank you all for the replies,I am going to my local Auto Electrical shop this week and hopefully it will be sorted.I will keep you informed.Thanks again.
Diarmaid

 

[diarmaid]

Thanks for your responses,my problem was the alternator pulley, my local auto electrics fixed it and my car is running much better.
Thanks to Ellsy Tanners for the good directions.
Diarmaid

 

[panason1c]

The freewheel clutch allows the alternator to slow down gradually when the engine is stopped, so not putting a strain on the drivebelt
John

The above is correct. The freewheel clutch is fitted for the reason to avoid excess loadings on the drivebelt on overun or engine shutdown situations.

 

[television]

The above is correct. The freewheel clutch is fitted for the reason to avoid excess loadings on the drivebelt on overun or engine shutdown situations.

Do you have any idea why they are only fitted to diesels

 

[panason1c]

Do you have any idea why they are only fitted to diesels

Hi television, I wasn't aware that they are only fitted to diesels but if that is the case i would guess that is because a diesel engine will 'stop' more abruptly due to the higher compression engine.




As is well-known in the art, an automobile alternator is typically provided mechanical power from a V-belt attached to the automobile's engine. This belt drives a pulley, or sheave, on the alternator. This sheave proceeds to turn a shaft which drives a rotor in the alternator. The rotation of this rotor generates electricity.
A problem occurs, however, in the use of an alternator. This problem occurs when the engine is driving an alternator at a given speed and the automobile's transmission is in a given gear. If the transmission upshifts to a higher gear, the engine speed decreases abruptly. As a result, the V-belt driving the alternator abruptly decreases in speed as well. However, typical alternator rotors have considerable rotational inertia, which opposes the V-belt's abrupt decrease in speed. As a result, the alternator actually attempts to drive the V-belt. However, the interface between the V-belt and the sheave frequently cannot carry the resultant torque, which can be quite large. As a result, the V-belt may slip on the sheave, causing an audible and annoying squeal. An overrunning clutch, which would prevent the alternator from attempting to drive the V-belt in the manner just described, would prevent the squeal.
An overrunning clutch used in an alternator would typically take the form of an outer cylindrical "race", which would be connected to the sheave; and an inner cylindrical race, which would be connected to the alternator rotor. Engaging means arranged between the races would allow the V-belt to drive the alternator but would "overrun", not allowing torque transmission, when the alternator attempts to drive the V-belt.
The use of a simple roller-type overrunning clutch, well-known in the art, would help eliminate the belt squeal. However, roller-type clutches have springs which hold each roller member which engages the two races. At the high speeds experienced by an alternator (upwards of 18,000 revolutions per minute), the springs in a roller-type clutch will typically allow the engaging members to disengage from the two races. When the alternator speed reduces, the engaging members will re-engage, typically with a significant shock. Such a shock is a detriment to the reliability of the clutch.

 

[television]

Thank you panosonic for taking the time to write that out, and yes it does fit in with what I know and thank you again

 

[panason1c]

Just to add ...... the reason freewheel clutches are in existence is because of the use of bigger and much more powerful altenators being used .....the bigger commutators carry a lot more momentum/energy than earlier, smaller units.

 

[television]

Just to add ...... the reason freewheel clutches are in existence is because of the use of bigger and much more powerful altenators being used .....the bigger commutators carry a lot more momentum/energy than earlier, smaller units.

Thank you,even though diesels use a little less current, they are getting bigger and even water cooled as well

 

[panason1c]

Thank you,even though diesels use a little less current, they are getting bigger and even water cooled as well

Yes, in the early days, diesels with 'mechanical' injection systems would barely use any electrical power, only enough to keep the 'stop' solenoid open but these days diesels are now fitted with 'electronic' injection systems, esp/abs pumps, post engine shutdown cooling fans and various other 'heavy consumption' ancillaries necessitates the need for large (100amp) batteries and the means to keep them fully charged = large, powerful alternators.