This repair manual covers 1967-1987 Chevrolet and GMC C/K 10, 20, and 30 full-size pickups. 2WD and 4WD, all 6-cylinder inline, 4.3L V6 and V8 gasoline engines. Also covers all Suburban, full-size Blazer and Jimmy, 1967-1991.

Note: this manual DOES NOT include diesel engine or GMC 305 cu.in. V6 gas engine information.

Book Excerpt: 1967-1987 Chevy, GMC Pickups, Suburban, Blazer, Jimmy Repair Manual GENERAL ENGINE OVERHAUL PROCEDURES

ENGINE BLOCK | CLEANING
(Refer to illustrations 14.1a, 14.1b, 14.8 and 14.10)

1. Remove the soft plugs from the engine block. To do this, knock the plugs into the block, using a hammer and punch (see illustration), and then grasp them with large pliers and pull them back through the holes (see illustration).
2. Using a gasket scraper, remove all traces of gasket material from the engine block. Be very careful not to nick or gouge the gasket sealing surfaces.
3. Remove the main bearing caps and separate the bearing inserts from the caps and the engine block. Tag the bearings, indicating which cylinder they were removed from and whether they were in the cap or the block, and then set them aside.
4. Using a 1/4 inch drive breaker bar or ratchet, remove all of the threaded oil gallery plugs from the rear of the block. Discard the plugs and use new ones when the engine is reassembled.
5. If the engine is extremely dirty it should be taken to an automotive machine shop to be steam cleaned or hot tanked.
6. After the block is returned, clean all oil holes and oil galleries one more time. Brushes specifically designed for this purpose are available at most auto parts stores. Flush the passages with warm water until the water runs clear, dry the block thoroughly and wipe all machined surfaces with a light, rust preventative oil. If you have access to compressed air, use it to speed the drying process and to blow out all the oil holes and galleries.
7. If the block is not extremely dirty or sludged up, you can do an adequate cleaning job with warm soapy water and a stiff brush. Take plenty of time and do a thorough job. Regardless of the cleaning method used, be sure to clean all oil holes and galleries very thoroughly, dry the block completely and coat all machined surfaces with light oil.

EMISSIONS CONTROL SYSTEMS

THERMOSTATIC AIR CLEANER (THERMAC)
(Refer to illustrations 12.2, 12.9, 12.15 and 12.20) GENERAL DESCRIPTION

1. The thermostatic air cleaner (THERMAC) system improves engine efficiency and drivability under varying climatic conditions by controlling the temperature of the air coming into the air cleaner. A uniform incoming air temperature allows leaner air/fuel ratios during warm-up, which reduces hydrocarbon emissions.
2. The system uses a damper assembly, located in the snorkel of the air cleaner housing, to control the ratio of cold and warm air directed into the carburetor or throttle body. This damper is controlled by a vacuum motor which is, in turn, modulated by a temperature sensor in the air cleaner (see illustration). On some engines a check valve is used in the sensor, which delays the opening of the damper, when the engine is cold and the vacuum signal is low.
3. It is during the first few miles of driving (depending on outside temperature) that this system has its greatest effect on engine performance and emissions output. When the engine is cold, the damper blocks off the air cleaner inlet snorkel, allowing only warm air from around the exhaust manifold to enter the engine. As the engine warms up, the damper gradually opens the snorkel passage, increasing the amount of cold air allowed into the air cleaner. By the time the engine has reached its normal operating temperature, the damper opens completely, allowing only cold, fresh air to enter.
4. Because of this "cold engine only" function, it is important to periodically check this system to prevent poor engine performance when cold, or overheating of the fuel mixture once the engine has reached operating temperatures. If the air cleaner damper sticks in the "no heat" position the engine will run poorly, stall and waste gas until it has warmed up on its own. A valve sticking in the "heat" position causes the engine to run as if it is out of tune due to the constant flow of hot air to the carburetor or throttle body.

Subject: 1967, 1968, 1969, 1970, 1971, 1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987 Chevrolet, GMC Pick-ups, Suburban, Blazer, Jimmy service, maintenance, and repair instructions. ISBN-10: 1850107645 | ISBN-13: 9781850107644 | Haynes 24064