420SE M116965 belt pulleys

[Llewelyn]

Last night I had a crazy failure of belt pulleys.

The viscous fan hub is getting noisy so I took it off to see if I could fix it (can't, but that's another story). Now, that's held on by the same 4 bolts that also hold the pressed-steel pulley on the water pump, as far as I can tell. However I had no reason to move the pulley so left that alone, and bolted the fan back on. The fan centre bit is still bolted solidly to the front of the pump, as is the pulley - and I'd driven over 100 miles yesterday (after looking at the fan on friday) with no issues bar the noisy fan hub.

However. Somehow, the pulley has gotten itself out of line, (water pump seems OK) and has fouled the crank pulley, deforming the groove that should have the alternator belt in it until the alternator belt has shredded. Thereafter, I got home by the good offices of the RAC so that means this year's membership was worth paying.

I've seen a couple of pulleys on eBay Germany. Are all M116 crank pulleys the same fitting, and can the pulley be got off without disturbing the centre crank bolt which holds the hub to which the pulley/vibration damper is bolted? It looks like it should be possible.

More info on how it managed to do this when I get it apart ...

 

[Llewelyn]

Also be useful to know if pulleys from other M116 engines will fit it.

 

[ivan1983]

This website should allow you to compare part numbers to be sure.

Mercedes Benz EPC Type W126 126 Information Everything Benz

At a guess I would say 380/420 pulleys would be the same probably 500/560 are interchangeable too. If the part numbers match you can confirm

 

[Llewelyn]

Turns out it's the water pump is the culprit. Bearings are noisy but still intact so it needs changing but the pulley failure is caused by the pressed on flange on the pump shaft has shifted about 10mm. How I have no idea as it still seems to be tight. This of course means the pulley was out of place and fouled the engine pulley.

 

[Llewelyn]

I see a bunch of water pumps badged variously as first line, QH, Valeo, Hella, Meyle - any of them I should avoid, or are all the 3rd party ones about equal?

 

[Llewelyn]

Just been studying the catalog, the 500 and 560 M117 engines use the same crank pulley as the 4.2 M116, the smaller M116s don't but the difference is probably the lack of the 5th groove to run the air pump for the SEL air suspension, which I don't need anyway. They show a superceded part number, which might be due to not bothering to fit a 4-groove pulley on non-SELs - mine is an SE and has the 5 groove pulley, but the 5th groove is not used. Pity I can't use that one for the alternator