Cooling Hole... Stock?

[erco]

My '67 has always had this D-shaped hole in the upper sheet metal. Is there supposed to be a plug or cover there?

[flat6_musik]

Maybe for the A.I.R. pump plumbing.

[bbodie52]

» Sun Dec 27, 2015 10:17 am

The confusion comes from the inconsistencies found in the GM documentation concerning the AIR system. In the two illustrations below, you can see some of those inconsistencies.

The first pictures comes from the Chevrolet Corvair Parts Catalog, while the closeup in the second picture comes from a GM assembly diagram. The parts catalog illustration shows no sign of the vacuum-controlled valves the assembly diagram shows. The latter are mounted on the air cleaner assembly and they are connected to intake manifold vacuum ports on the rear of the carburetor pads.

Secondary air injection (commonly known as air injection, or colloquially smog pump) is a vehicle emissions control strategy introduced in 1966, wherein fresh air is injected into the exhaust stream to allow for a fuller combustion of exhaust gases...The first systems injected air very close to the engine, either in the cylinder head's exhaust ports or in the exhaust manifold. These systems provided oxygen to oxidize (burn) unburned and partially burned fuel in the exhaust before its ejection from the tailpipe...Pumped air injection systems use a vane pump turned by the engine via a belt or electric motor. The pump's air intake is filtered by a screen to exclude dirt particles large enough to damage the system. Air is delivered under pressure to the injection point(s). A check valve prevents exhaust forcing its way back through the air injection system, which would damage the pump and other components...Carbureted engines' exhaust raw fuel content tends to spike when the driver suddenly releases the throttle. To prevent the startling and potentially damaging effects of the explosive combustion of this raw fuel, a diverter valve is used. This valve senses the sharp increase in intake manifold vacuum resulting from the sudden closure of the throttle, and diverts the air pump's outlet to atmosphere. Usually this diverted air is routed to the engine air cleaner or to a separate silencer to muffle objectionable pump noise.

The design shown in the assembly diagram looks like a design that handles the function of the diverter valve differently. The Wikipedia article states that the pump's air intake is filtered by a screen. The diverter valve mentioned in the Wikipedia article diverts the pumps air outlet to atmosphere. As far as I can determine in the assembly diagram, it looks like the AIR pump's inlet is filtered by the engine air cleaner, and that this air is controlled by some type of cutoff valve mounted on each side of the air cleaner assembly. Two vacuum lines are tied to the rear side of each carburetor mounting pad, and each vacuum line is connected to the bypass valves mounted on each side of the air cleaner assembly. I'm guessing that a closed throttle raises manifold vacuum, which probably closes the valves mounted on the air cleaner assembly — starving the AIR pump for air from the air cleaner assembly. This would effectively block the AIR pump's output to the exhaust manifolds. Instead of diverting the AIR pump's outlet to atmosphere (as described by Wikipedia), the AIR pump's inlet is cut off from its fresh air source (the air cleaner) when the intake manifold vacuum spikes, which has the same effect as an outlet diverter valve by stopping the air output to the exhaust ports, which prevents the "startling and potentially damaging effects of the explosive combustion of this raw fuel...". Apparently the design of the AIR system used on the Corvair changed during production, and the design change did not show up in all Chevrolet documentation. The parts catalog illustration (used by Clark's Corvair Parts) shows a design using an outlet diverter valve, while the assembly book shows a different design using a bypass valve on the air cleaner assembly that blocks the smog pump inlet instead of diverting the smog pump output. (Or something like that).

The Clark's Corvair Parts online catalog lists a 1965 Corvair Chassis Shop Manual, and also four supplements for 1966, 1967, 1968 and 1969. Perhaps those four shop manual supplements describe the variety of AIR (Smog) emissions control systems manufactured in the final four years of Corvair production. We know there were domed pistons in some engines, and a variety of distributor advance curves that were implemented to try to make the AIR system work better. Perhaps the GM engineers were relieved when the Corvair was discontinued and they didn't have to struggle anymore to try to satisfy the smog police and the Corvair owner too!

the '66 turbo has,
no hole on the oil cooler side.
no second v belt on crank pulley.

[erco]

Thanks guys, I had not considered that. Something to close up at teardown.

My '67 140HP Monza has a 110 badge, so somebody swapped engines before I got it. It was a South Carolina car, I presumed AIR injection was a California thing and my car never had it. Brad's post shows there was a variety of unsightly plumbing in that era. Sure messed up the simplicity of this little motor.

[bbodie52]

You should see what this mandated anti-pollution system did to the exhaust manifolds! From what I remember as a 17 year old rebuilding the engine, the exhaust manifolds had an air injection tube protruding several inches from each manifold exhaust opening into each cylinder head exhaust port. This squirted air from an air injection passageway that was cast into the manifold and directed the output from the A.I.R. (Smog) pump. I don't think the Corvair engines liked this intrusion into their happy air-cooled world.

I took one apart in 1970 to rebuild a neighbor's blown engine (disintegrated piston — he apparently had it let go at freeway speeds and left it in DRIVE while he coasted to a stop. It appeared that the Powerglide transmission and transaxle continued to rotate the engine crankshaft with the connecting rod banging away in the crankcase while shredded aluminum circulated through the oil passages.


The SMOG Pump system tended to cause a hot-running engine. The GM engineers were struggling every year to make it run better and to satisfy the government bureaucrats that oversee the various anti-pollution mandates.