See Figures 1, 2, 3, 4, 5 and 6
One form or other of this system is found in most models sold in the 50 states. The managed air Thermactor emission control system makes use of a belt-driven air pump to inject fresh air into the hot exhaust stream through the engine exhaust ports. The result is the extended burning of those fumes which were not completely ignited in the combustion chamber, and the subsequent reduction of some hydrocarbon and carbon monoxide content of the exhaust emissions, by turning them into harmless carbon dioxide and water.
The managed air Thermactor system is composed of the following components:
- Air supply pump (belt-driven)
- Air bypass valve
- Check valves
- Air manifolds (internal or external)
- Air supply tubes (on external manifolds only)
Air for the Thermactor system is cleaned by means of a centrifugal filter fan mounted on the air pump driveshaft. The air filter does not require a replaceable element.
To prevent excessive pressure, the air pump is equipped with a pressure relief valve which uses a replaceable plastic plug to control the pressure setting.
The Thermactor air pump has sealed bearings which are lubricated for the life of the unit. The pump also utilizes a preset rotor vane and bearing clearances, which do not require any periodic adjustments.
The air supply from the pump is controlled by the air bypass valve, sometimes called a dump valve. During deceleration, the air bypass valve opens, momentarily diverting the air supply through a silencer and into the atmosphere, thus preventing backfires within the exhaust system.
A check valve is incorporated in the air inlet side of the air manifolds. Its purpose is to prevent exhaust gases from backing up into the Thermactor system. This valve is especially important in the event of drive belt failure, and during deceleration, when the air bypass valve is dumping the air supply.
The air manifolds and air supply tubes channel air from the Thermactor air pump into the exhaust ports of each cylinder, thus completing the cycle of the Thermactor system.
Another version of the Thermactor system is the called the Thermactor II or pulse air system. Instead of an air pump, this system uses natural pulses present in the exhaust system to pull air into the exhaust manifold through pulse air valves. The pulse air valve is connected to the manifold with a long tube and to the air cleaner or silencer with a hose.
The entire Thermactor system should be checked periodically according to the maintenance chart in General Information & Maintenance . Use the following procedure to determine if the system is functioning properly.
See General Information & Maintenance for belt adjustment and replacement procedures.
- Remove the air cleaner assembly, if necessary.
- Inspect all components of the Thermactor system for any loose connections or other abnormal conditions. Repair or replace them as necessary.
- If so equipped, inspect the air pump drive belt for wear and tension. Adjust or replace it as necessary.
- With the transmission in neutral or park and the parking brake on, start the engine and bring it to normal operating temperature.
- Stop the engine and connect a tachometer. Remove the air supply hose at the check valve. If the engine has two check valves, remove both air supply hoses at the check valves and plug off one hose. Position the open hose so that the air blast emitted is harmlessly dissipated.
- Start the engine and accelerate to 1,500 rpm. Place a hand over the open hose. Air flow should be heard and felt. If no air flow is noted, the air bypass valve is defective and should be replaced. The procedure is outlined later in this section.
- Let the engine speed return to normal idle. Pinch off and remove the vacuum hose from the bypass valve. Accelerate the engine to 1,500 rpm. With a hand held over the open end of the check valve hose (same as in Step 6), virtually no air flow should be felt or heard. If air flow is noted, the bypass valve is defective and should be replaced.
- Let the engine speed return to normal idle and reinstall the vacuum hose on the bypass valve vacuum hose nipple. Check hose routing to be sure it is not pinched or restricting normal vacuum signal flow.
- With a hand held over the open end of the check valve hose (same as in Step 6), rapidly increase the engine speed to approximately 2,500 rpm. Immediately release the throttle so the engine returns to normal idle. Air flow should be felt and/or heard momentarily diminishing or cutting off completely during deceleration. If the air flow does not momentarily diminish or cut off, repeat this procedure using an engine speed of 3,000-3,200 rpm. If air flow does not respond correctly during the deceleration from 3,000-3,200 rpm, the vacuum differential control valve should be replaced. Of course, this step should be omitted if the system is not equipped with a differential vacuum valve.
- Accelerate the engine to 1,500 rpm and check for any exhaust gas leakage at the check valve. There should be virtually no pressure felt or heard when a hand is held over the open end of the check valve for approximately 15 seconds. If excessive leakage is noted, replace the check valve(s).
- If the engine is equipped with two check valves, repeat Step 10 for the second valve.
- Stop the engine and remove all test equipment. Reconnect all related components and reinstall the air cleaner, if removed.
REMOVAL & INSTALLATION
Thermactor Air Pump
See Figures 7, 8, 9 and 10
- Disconnect the air outlet hose at the air pump.
- Loosen the pump belt tension adjuster.
- Disengage the drive belt.
- Remove the mounting bolts and air pump (or air pump and bracket assembly).
- Position the air pump (or air pump and bracket assembly) and install the mounting bolts.
- Place the drive belt in the pulley and attach the adjusting arm to the air pump.
- Adjust the drive belt tension to specification and tighten the adjusting arm and mounting bolts.
- Connect the air outlet hose to the air pump.
See Figure 11
- Loosen the air pump adjusting arm bolt and mounting bracket bolt to relieve drive belt tension.
- Remove the drive pulley attaching bolts and pull the drive pulley off the air pump shaft.
- Pry the outer disc loose, then pull off the centrifugal filter fan with slip-joint pliers.
- Install a new filter fan by drawing it into position, using the pulley and bolts as an installer. Draw the fan evenly by alternately tightening the bolts, making certain that the outer edge of the fan slips into the housing.
A slight interference with the housing bore is normal. After a new fan is installed, it may squeal upon initial operation, until its outer diameter sealing lip has worn in, which may require 20-30 miles of operation.
- Disconnect the air supply hose at the valve. (Use a 1 1 / 4 in. crowfoot wrench; the valve has a standard, right-hand pipe thread.
- Clean the threads on the air manifold adapter (air supply tube on the 8-302 engine) with a wire brush. Do not blow compressed air through the check valve in either direction.
- Install the check valve and tighten.
- Connect the air supply hose.
Thermactor Air Bypass Valve
- Disconnect the air and vacuum hoses at the air bypass valve body.
- Position the air bypass valve, and connect the respective hoses.
Vacuum Differential Control Valve
- Remove the hose connections.
- Unbolt the valve at its mounting bracket.
- Install in reverse order.