Just curious, does anyone know why the spacing of the fan blades round the hub on Mercedes cooling fans is non-regular?

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RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)

I imagine it has something to do with the noise generated. I wouldn't try to even them out!

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Probably balance as well.
Best not try & improve what MB spent time & $$ optimizing.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

I believe most cars with larger fans are like this. I think it's to cancel some of the roar and harmonics.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250

I've always thought it was to allow room to get to the crankshaft bolt.

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Jim

combination of both, allows room to work and reduces the blade pass frequency noise by changing the seperation distances. it give you # of blade different frequencies at low amplitude where an evenly spaced blade pattern gives one frequency at a high amplitude. They also use prime number of blades to eliminate multiple orders of frequencies

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)

For the same reason the tread on tires is not regular around the circumference. Even spacings generate a few specific frequencies while the uneven spacing gives some variation to the frequencies at any constant rpm.

Think how vibrato 'improves' a single musical note.

What would be an example of a non-prime number of blades?

6 is non-prime

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Cheers!
Scott McPhee

1987 300D

I thought the distribution of blades had something to do with balancing the loads on the water pump?

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Cheers!
Scott McPhee

1987 300D

If that was the case the fan would have to be "keyed" to the pump and fixed.

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Jim

How would uneven spacing improve balance?

So is it really non-prime numbers that are a problem? Or is it even numbers? Or is it both?

Maybe you should be counting the ' spaces ' instead of the blades...
both in number and spacing...

http://en.wikipedia.org/wiki/Lockheed_YO-3

http://www.yo-3a.com/yo3a6918007.html

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/diesel-discussion/156207-photo-step-step-post-showing-w123-evaporator-removal-1983-240d-1982-300td.html?highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html

number of blades determines number of spaces, but its the trailing edge of the blade that makes the noise

primes are 3, 5, 7, 11, 13, 17 etc

heres why.


take an 8 blade fan, it will generate frequencies at multiples of 8, 4, 2, and 1

a 12 blade fan will generate frequencies at multiples of 12, 6, 4, 2, 3, 1

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1982 300CD Turbo (Otis, "ups & downs") parts for sale
2003 TJ with Hemi (to go anywhere, quickly) sold
2001 Excursion Powerstroke (to go dependably)
1970 Mustang 428SCJ (to go fast)
1962 Corvette LS1 (to go in style)
2001 Schwinn Grape Krate 10spd (if all else fails)