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  #1  
Old 11-29-2002, 12:31 AM
E's Benz
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Question Drive Belt Routing 1973 280SEL 4.5

I am looking for a drive belt routing diagram for my 1973 280SEL 4.5, (117.984 engine.)

I don't have the owner's manual, but I have the Chilton's Manuals from 1968-1973, (which doesn't have the diagram,) and the 1974-84, (which doesn't seem to have the right one in it.

Any help would be greatly appreciated.
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  #2  
Old 11-29-2002, 01:13 AM
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Join Date: Jan 2002
Location: NY
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I'm not sure if this is for you engine. This page from W126 CD for 116 and 117 engines:
Attached Files
File Type: zip belts116-117.zip (26.8 KB, 55 views)
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  #3  
Old 11-29-2002, 01:42 AM
E's Benz
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Thanks myarmar.

One of my concerns was the double v-belt for the coolant pump. I was not sure if this was stock, but the diagram shows that it is correct.

I had a couple of questions from the diagram: What is the secondary air injection pump for? Do you happen to know the length of this belt?

This diagram has been a great help. Now I can get the rest of the belts and replace them all - as soon as I get the rest of those fan bolts off!
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  #4  
Old 11-29-2002, 01:35 PM
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Belt A:
p/n A 006 997 35 92 V-belt set 2 pieces, 9.5X1160
Belt B:
p/n A 004 997 85 92 V-belt alternator, 9.5X1000
Belt C:
p/n A 005 997 82 92 V-belt AC comp,
12.5X868
No belt D on your engine ?
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  #5  
Old 11-29-2002, 10:26 PM
E's Benz
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Arrow

No. My engine does not have the 'D' belt and associated pulley/pump.

Should I be worried about that, or is it just a variation of the engine?
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  #6  
Old 11-30-2002, 12:07 AM
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Join Date: Jan 2002
Location: NY
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No, don't worry. Back in 1973 MB did not use it. Here is old post with the theory behind it from Steve Brotherton:
Quote:
Originally posted by stevebfl
A.I.R. pump not Air pump. Air Injection Reaction. The point totally being that the unburned products of combustion were allowed to continue combustion in the exhaust using the wasted heat also going out.

First used in 1968 the process was usually accomplished with reactors as part of the exhaust manifolds. After the introduction of oxidation catalytic convertors in 1974 (MB waited till 75) the pump provided the oxygen necessary for the catalytic reaction. Big problem though, the system worked so well it burned the Nitrogen going alone for a ride forming NOX (various oxides of Nitrogen). So, in 1979-80 the new requirements necessitated redox cats (oxidation/reduction). In this system the NOX gases of combustion are reduced (chemical term for the opposite of oxidize - not term for making smaller) into the individual components - Oxygen and Nitrogen. The oxygen is then used to facilitate the oxidation area of the catalyst.

With these catalysts the need for exact fuel control became necessary. The idea being that if the exact amount of fuel and air were introduced then their by products would be in the proper proportions to be totally cleaned through catalytic action (without severe overheating). This control was gotten by measuring the quantity of oxygen in the exhaust. By allowing this quantity to swing back and forth (rich and lean - within a small window) an average exact amount is obtained while assuring a sufficient amount of oxygen to fuel the process.

Now comes the modern AIR pump. If it were to work during the above closed loop fuel control the whole system is screwed. The air injected would overwhelm the oxygen sensor and the management system would go full rich to try and compensate. Air injection is an absolute NO-NO on a post 1980 lambda controlled car. EXCEPT, during cold operation where the O2 sensor and catalyst aren't hot and are not yet doing their job. During this time the AIR pump is doing two things. First it is working like the 1968 car without a catalyst and second the fire that is causes is heating the O2 sensor and catalyst to hasten lambda conditions.

Soooo....the AIR pump on a 420SEL only works when cold (it is activated by an electro-magnetic clutch similar to the A/C compressor), it only works in the exhaust and it does nothing to engine performance. The only long term mechanical effects to its loss would be the additional carbon build-up through prolonged cold catalytic inaction.


[Edited by stevebfl on 03-03-2001 at 01:14 PM]
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  #7  
Old 11-30-2002, 02:39 AM
E's Benz
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Whew!

It's just an emissions control measure that my car doesn't have.

By the way, thanks for the part numbers.
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