The Stovebolt Site Forums The Shop Area Engine Shop Vented Valve Cover - Why ? 1954 3604

Was just reading another post about valve covers and noticed that the valve cover for the 1954 235 engine has vents according to the image provided by Pre 68' Dave in TIms post. My 54' which has the original engine (or at least its a 54' engine 0056074F54XA ) has a non vented valve cover. Question - is it important that it be vented? Should I use a vented oil filler cap ?

In order for the road draft tube (or PCV valve) to vent the crankcase properly there must be a way for air to get into the engine. At speeds above 30 MPH the air passing the end of the draft tube creates a vacuum to create a flow through the crankcase, and air from the vent(s) flows into the engine. If the valve cover doesn't have slots, you need a vented filler cap or some other way to get air in.
Jerry

yes, it helps prevent moisture build up. I couldn't figure it out way long ago, so I smashed them shut and soldered them up, then 20 years later I took the cover off and there were sheets of rust that had fell off. Not to mention that is how the crankcase was vented on many of the engines.

Okay, I get it, thanks for the explanation . I'll put a vented filler cap on it . Thanks Jerry ! Thanks brokenhead !

Another reason is you will most likely develop a oil leak, probably around the front or rear pan seal, maybe a rear main seal leak with out the vented cap. Excessive pressure will build. Oddly enough, Chevrolet did not put a vented cap with the road draft tube on the solid lifter 270 hp and up engines in the 283 in 1959/1960. Many developed leaks after the fact.

Thanks Steve, I'm glad I asked the question, all of these explanations make sense. Good thing you guys are around to help me stay out of trouble.
Thanks Everyone.

If you look at a 216 after a long highway run, you will see fumes wafting from the vents in the valve cover at idle or after shutdown. These are fumes coming from the crankcase. Since the draft tube does nothing at idle, the vents are there to let it out.

Pressure will leave by the road draft tube.

What pressure are you referring to?
And under what condition will this "pressure leave by the road draft tube?
I am certain that it is clear in your mind, but I need more information to determine what you are referring to.

A previous post: "Another reason is you will most likely develop a oil leak, probably around the front or rear pan seal, maybe a rear main seal leak with out the vented cap. Excessive pressure will build"

The only time the PCV is not pulling air from the crankcase is when the engine is not running. The filter in the side of the breather is to prevent dust from being drawn into the engine, the same thing the horsehair packing in a vented oil filler cap did. The slotted valve cover let all kinds of dust in, and was at least partly responsible for the short piston ring and bearing life of those engines. When the "closed loop" PCV systems came about, engine life virtually doubled due to less contamination in the oil, and more effective purging of blow by and acids formed by humidity and combustion gases getting together.
Jerry

Those slits in the valve cover might also have allowed water to enter over the head, if the cowl-vent-scoop drain hose was short or poorly routed/positioned.

Per Jerry's post above about dirt getting into the system, I have seen where folks back in the day added a nipple to the valve cover and another one to the top of the air filter and connected them with a length of rubber hose to allow filtered air into the engine. The packing in the oil breather caps doesn't offer that type of protection and open slits in the valve cover certainly don't.

I have seen old engines with this type of installation that have had the valve cover slits brazed or welded shut. I have seen it done with homemade nipples and ones with 90 degree bends and flat mounting flanges that took two screws and a gasket that look like they must have been sold as some kind of a kit because they are all the same and look as though they were made for that very purpose.

I seem to recall that Jerry has posted in the past that California passed early emissions laws that required installation of a PCV and a filtered breather system. When I see the retrofits mentioned above combined with early PCV plumbing that was obviously installed back in the day, I figure that it was probably a CA vehicle. But I sometimes find the venting retrofits on engines that still have road draft tubes, so some people were obviously simply trying to let the engines breath with filtered air regardless of emissions laws for the reasons described by Jerry.

Matt

Good point Tim.

Since I owned a shop in central California in the mid-1970's I installed dozens, if not hundreds of those PCV retro-fit kits. At that time the California Air Resources Board (Yep- - - -CARB) was operating roadside emissions testing- - - - -pulling over a bunch of cars for a visual under hood inspection and an exhaust emission test, there was a huge amount of pressure for compliance. The fines were very steep for running an unmodified vehicle or one that had a smoky exhaust. Later the SMOG test was only required when a vehicle changed ownership, but a visibly smoky tailpipe still got the driver ticketed.
Jerry

Roger that. Only exception to that would be if the road draft tube was completely clogged up, but if that were the case then one has a much bigger issue than just leaky seals.

Jerry, I remember those roadside checks,, for smog,,brakes,,headlight alignment ,,cracked glass,,bald tires,,etc... back in the '70s.
The Richfield station I worked at , we would also push a tapered rubber plug in the road draft tube when we installed those closed system PCV's
And a smog check consisted of a "certified" smog check station doing a visual,,and scribbling out a carbon copy form stating my car was O.K.

Getting that "Certified Smog Check Station" placard took some pretty creative financing- - - - -usually involving a contribution to the right member of the CARB board! That's probably why my shop never got one!
Jerry