Re: [OMC-Boats] Pcv breather

From: Lee Shuster <Lee.Shuster@...>
Date: Fri, 11 Sep 2009 15:57:50 -0600

Typically on boats of this vintage there is no Positive Crankcase Ventilation in the now-common automotive "PCV" valve sense.

The standard OMC procedure was to connect a valve cover breather (rubber) hose between each valve cover on a V-block engine and the outside of the flame arrestor.

The theory being as the engine throttle was opened the crankcase is ventilated by the pull of the low pressure into the carb. And re-cycling these back thru the carb, allows the engine to burn off these elements. One probably can't measure it, but in theory, at least, this helps increase fuel economy.

Proper crankcase ventilation is important to allow "blow-by" fumes and gases somewhere to go. PCV valves were introduced on cars in the mid 1960's (earlier in California). Autos with PCV's differ (compared to our boats) by having a one-way check valve and instead of being routed into the carb inlet the are usually routed directly into a intake manifold "vacuum" port.
Prior to PCV's you would typically see a meshed valve cover breather cap and have a road draft tube, but remember cars have free air access, not an enclosed engine compartment.

Here's the "big deal" if you don't RE-connect you hoses: You engine compartment will gradually get filled with these blow-by gases which are potentially explosive, and depending on how "tight" you engine is a messy, oil film will appear on everything. It's also not so good for the environment (and your health) as the blow-by gases contain small amounts of unburned hydrocarbons. Chrome breather caps look cool, but will merely vent inside the engine compartment. Resist the temptation to use them and get your rubber hoses hooked back up. I know, you'll say you don't know where to find them, but they are out there.

I've actually installed an auto style PCV on my small block Chevy. It did require re-adjusting my idle jets slightly.
I've installed a clear catch can/filter so I can monitor or trap the heavy stuff.


-----Original Message-----
From: omc-boats-bounces@... [] On Behalf Of jd
Sent: Friday, September 11, 2009 2:55 PM
To: Evinrude and 70's & Johnson Boats of the 1960's
Subject: [OMC-Boats] Pcv breather

What is the PCV valve breather for and is it a big deal if it's not connected?

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Received on Friday, 11 September 2009

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