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Author Topic: Mickey Thompson Valve Covers  (Read 5044 times)
cschaefer
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« on: January 25, 2007, 10:17:09 AM »

My son has a base model '68 coupe, one owner CA car. Nice. He would like to put some very nice early '70s Mickey Thompson finned valve covers on it but does not want to drill holes in the covers for the breather element or the PCV valve. Since it already has the tube-fill type oil fill, one idea was to put the 67 oil fill tube in with the screw-in PCV valve, but what about the breather?

Any other creative ideas?

Thanks a lot.
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sam
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« Reply #1 on: January 25, 2007, 10:29:59 AM »

If the motor does not have a road draft tube in the back you can put a breather on the oil  fill tube. Some oil fill tubes have a screw type cap and some a push-on style. Most valve covers need to have some type of breathing.  Sam
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cschaefer
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« Reply #2 on: January 25, 2007, 10:35:48 AM »

Sam,

Thank you. It does not have a rod draft tube and come to think of it, i have seen breather caps on oil fill tube, but what about the PCV vavle?

Carl.
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JohnZ
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« Reply #3 on: January 25, 2007, 11:13:27 AM »

If all you have is an oil fill tube with a vented cap, all you'll have is pressure relief, not crankcase ventilation, and it'll blow hot oil mist out of the cap. The PCV system needs two things:

1. An "intake" where fresh air is drawn into the crankcase - either a hose from the passenger side valve cover to the air cleaner base (like the stock setup), a breather on the passenger side valve cover, or an oil fill tube with a vented cap.

2. An "exhaust" where the flow of crankcase fumes are drawn and metered from the driver's side valve cover, through a PCV valve, to the 3/8" PCV port on the carb base (like the stock setup).

Both (1) and (2) are required to ensure a continuous flow of outside air through the crankcase and into the intake manifold. There are options for (1), but not for (2).
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'69 Z/28
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rich69rs
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« Reply #4 on: January 25, 2007, 06:29:30 PM »

By the mid '60's, Chevy had introduced crankcase ventillation on its SB engines.  The earliest systems were "open" systems that drew air in from the breather in the oil filler cap at the front of the engine, through the engine, and then from the engine through the PCV valve to the base of the carb.  283 and 327 engines in the mid '60's had a fitting at the back of the block, near the distributor.  A hose was connected to this fitting at the back of the engine.  The hose also had an in line PCV valve with the other end of the hose connected to the base of the carb.  Scavenging air flow was through the breather in the oil filler cap at the front of the engine, through the engine, out the engine at the back, through the PCV valve, and into the base of the carb.  This system is an open system in that funes can vent out the oil filler breather.  You can readily see this,  especially just after the engine is turned off.  My '66 Chevelle (283 engine) has this arrangement.

When the transition was changed to a "closed" crankcase ventillation systems, the oil filler cap no longer had a breather and was changed to a sealed cap.  The connection at the back of the engine was eliminated with the PCV valve being moved to LH valve cover.  Scavenging air flow was through the seperate filter in the air cleaner, into the engine, out through the PCV valve, and into the base of the carb.   In 1969, the oil fill tube was eliminated at the front of the engine with the oil fill sealed cap moved to the LH valve cover.  My '69 RS (327 engine) has this arrangement.

As previously stated, you have to be able to draw filtered scavenging air into the engine in metered quantities, which varies with engine vacuum, and exhaust it into the air fuel mixture at the carb.  If your engine is supposed to have an operative PCV system and you "plug" it, all kinds of mischief can occur including corrosion, dillution of the oil, and sludge.
« Last Edit: January 25, 2007, 06:50:48 PM by rich69rs » Logged

Richard Thomas
1969 RS
Oregonjam
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« Reply #5 on: July 06, 2009, 12:26:16 PM »

Rich,

 What if you opted to run a double breather. One on each valve cover with no PCV and an open filter element?

This is my situation. I just broke in the original motor for my 68 SS 350. I do not have the original air cleaner ready yet so have an open element on it. A breather on the left valve cover and a PCV on the right that went to the carb base. I checked my plugs and 6 and 8 were fowling. I removed the PCV to try to trouble shoot it and see if my Rings did not seat or I have bad valve guides. I was thinking that I was having excessive oil flow through the PCV to the Carb so temproarily eliminated it. I adjusted the idle about 50 rpm to compensate for the loss of the PCV.

Will tis cause more problems or do yo think it will work for a temp setup?

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68 07D SS350
John
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