Crankcase breather configuration - Mercedes-Benz Forum

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post #1 of 5 (permalink) Old 06-12-2012, 05:27 PM Thread Starter
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Vehicle: 1966 250S
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Crankcase breather configuration

Hi All,

I've got a '66 250s import from Germany that appears to have an original road draft tube attached to the crankcase breather and a paint-matched metal plug capping the pipe coming off the air intake cover over the carbs. I never made the connection between these pieces until just now and after doing some research online I see most of these engines seem to have the breather hoses connecting the crankcase directly to the air intake cover, at least here in the U.S.

I'm thinking of changing this setup to start recirculating the blow-by gases, because it would be better for the environment and might help with oil drips and cabin smell. What I can't tell is if there is a PCV valve involved in the setup or not. From photos it pretty much looks like there isn't, with just the rubber breather hose connecting the valve cover to the carbs' cover.

Can anyone confirm this setup? Is there anything else I should be aware of before making this change?

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post #2 of 5 (permalink) Old 06-13-2012, 06:49 PM
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The top vent pipe goes to the top carb cover. They are available.

Near Manassas Va. '65 220S, 2006 Ford Crown Victoria Police Interceptor, '99 Volvo V70, '72 350SL 4 speed

Not part of the in-crowd since 1952. It's BRAKES not breaks. You break a bone, use brakes to stop your car. /rant
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post #3 of 5 (permalink) Old 06-13-2012, 08:14 PM Thread Starter
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Thanks, wbain. I have all the parts, though on closer inspection my breather hose is pretty cracked, so I've ordered a replacement. I was just trying to make sure there wasn't a PCV valve in there somewhere. I'm pretty sure there's not, based on EPC schematics.
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post #4 of 5 (permalink) Old 06-14-2012, 08:35 AM
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Not a pvc valve just a small hole to meter the air volume

If you see vapors from the down tube and when you open the oil filler,,,,
There should not be any.

Brian O
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post #5 of 5 (permalink) Old 06-14-2012, 10:02 AM Thread Starter
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Thanks bostosh. I don't see smoke or anything like that if that's what you mean, but I know the vapors are there.

I went ahead and made this change yesterday, and I have two observations. I think I've lost a little power... not much but a noticeable amount. I assume this is due to blow-by gasses displacing a small amount of air with higher oxygen content at the carb intakes, and I think I can compensate for it with a little carb tuning.

The other thing I've noticed is a decreased odor level. Usually when parking the car in the garage right after a drive, the kitchen next door smells of fumes for a while. This is understandably annoying to my wife, so I usually park the car outside for a while to cool off before driving in. This morning I went out for a long spin and pulled right into the garage when I got back as a test (wife wasn't home). Don't get me wrong, the garage still smells like a hot old car, but the kitchen wasn't affected at all, so I'm chalking this up as a victory.

On closer inspection, I can't tell if the road draft tube was original or not. It's just a bent plastic tube that was inserted into the end of the breather hose and then held in place by a bracket on the driver's side of the engine near the bottom. The plug in the carb cover was shiny rubber, not painted metal like I initially thought. It still seems to have been a purpose-built plug, though.
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