Author Topic: 6.9 V-belt sizes  (Read 362 times)

raueda1

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6.9 V-belt sizes
« on: 21 April 2021, 05:08 PM »
I'm replacing my belts as their age and history are unknown.  Try as I might, I can't find the sizes anyplace and I don't trust the "size selector" things on websites.  Better to just look at what's there:

Alternator:                     10x1200
Steering/H2O pump:  2x 13x1200
Air Con:                        13x1000

The question is the alternator belt.  Is the 10x1200 alternator belt really right?  Why would it be skinnier than the others?  The pulleys all look about the same width.  Can anybody confirm or deny?  Vielen Dank im Voraus und cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Max-NL

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Re: 6.9 V-belt sizes
« Reply #1 on: 22 April 2021, 02:50 AM »
From the workshop manual, don't know why the alternator belt is skinnier (A = waterpump/power steering belt, B = Air pump belt, C = AC belt, D = Alternator belt) :
1971 R107 350 SL (Dad's)
1975 W116 280 S (Dad's)
1975 W116 450 SEL 6.9 #140 (Dad's)
1977 W123 230 (Mine)
1992 W124 230 CE (Mine)

raueda1

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Re: 6.9 V-belt sizes
« Reply #2 on: 22 April 2021, 07:11 AM »
From the workshop manual, don't know why the alternator belt is skinnier (A = waterpump/power steering belt, B = Air pump belt, C = AC belt, D = Alternator belt) :
Problem solved.  Thanks very much!  I don't know why I can never find this stuff.   :o  Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: 6.9 V-belt sizes
« Reply #3 on: 22 April 2021, 10:19 AM »
Dave I think you have Euro model so this may not apply to you, but on US model with Aux trans pump you need a slighty longer belt on the AC belt run to accomodate the pulley on the trans pump.
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: 6.9 V-belt sizes
« Reply #4 on: 22 April 2021, 01:34 PM »
Dave I think you have Euro model so this may not apply to you, but on US model with Aux trans pump you need a slighty longer belt on the AC belt run to accomodate the pulley on the trans pump.
Hmmm.  I'm not so sure.  The belt that came off the car corresponds to Max-NL's table except mine was 13 mm wide instead of the euro 12.5 mm width.  My car has an idler pully exactly where the trans pump would be on a USA car.  I know this cause I've got a USA trans pump and at one point was considering installing it.  I dropped that idea but not before looking closely at the fit.  Incidentally, that pulley makes the AC belt a snap to change, much easier than the others.  Loosen 1 bolt and it's off! 

On an unrelated but interesting note, I've been working on the doors.  Lurking within I discovered somebody's idea of the obligatory USA side impact protection.  This consisted of a steel pipe with a bolt hole in one end and a steel rod telescoped into the pipe with a nut welded to the end of that.    They telescoped the whole thing into the door and glued the middle together.  The whole thing was then bolted inside the door.  I had to cut it out.  Somewhat clever but totally ghetto.  Other than a USA speedometer this is the only evidence I can find of any work done to import the car into USA.  I'm really not sure how they got away with it.

Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

ptashek

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Re: 6.9 V-belt sizes
« Reply #5 on: 22 April 2021, 05:38 PM »
Why would it be skinnier than the others?

If the alternator shorts in operation it could stall the engine, or make the belt slip hard causing a fire hazard.
That's why the belt is made the weak point in that link.
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1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

raueda1

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Re: 6.9 V-belt sizes
« Reply #6 on: 24 April 2021, 08:03 AM »
Why would it be skinnier than the others?

If the alternator shorts in operation it could stall the engine, or make the belt slip hard causing a fire hazard.
That's why the belt is made the weak point in that link.
Interesting, thanks.  Years (decades?) ago I did have an alternator seize once in another car.  As I recall the belt got fried but the car kept running off the battery long enough for me to get home.  Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

Mick74

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Re: 6.9 V-belt sizes
« Reply #7 on: 24 April 2021, 02:44 PM »
This thread is very timely for me, as I've been listening to a squealing alternator belt for a while now (only above 3000rpm, admittedly) and I think that the problem is a slightly oversized belt. Try as I might, I can't tighten it enough to stop it. Spurious belts from motor factors.
I've heard great things about Contitech belts, so I'm going to try those, or I might even go to the main dealer! You'd never know; I actually got plastic body pins for the sill chrome strip from my local dealer last year. The parts guy was into older Mercedes too.
1979 6.9 #6475

UTn_boy

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Re: 6.9 V-belt sizes
« Reply #8 on: 25 April 2021, 03:40 AM »
If you think 10mm width is small, you should get a load of the two belts for the left and right alternators on the majority of 600's.  They're only 7mm wide. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex

raueda1

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Re: 6.9 V-belt sizes
« Reply #9 on: 25 April 2021, 09:31 AM »
If you think 10mm width is small, you should get a load of the two belts for the left and right alternators on the majority of 600's.  They're only 7mm wide.
LOL, fantastic!  And 2 alternators no less.  Now I have alternator envy.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

UTn_boy

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Re: 6.9 V-belt sizes
« Reply #10 on: 25 April 2021, 07:03 PM »
If you think 10mm width is small, you should get a load of the two belts for the left and right alternators on the majority of 600's.  They're only 7mm wide.
LOL, fantastic!  And 2 alternators no less.  Now I have alternator envy.

That envy would quickly dissipate if the right alternator belt ever broke on you.  It's the very first belt you put on, and the last one to come off.  You'd have to remove 6 belts just to get to that one......none of which are at all pleasurable to remove. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1971 280sel Black/black leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex