SBC Head Bolt Torque Specifications

In 1955, GM took the automotive world by storm with the introduction of the Chevrolet Small Block V8 Engine. The SBC was originally designed for the Corvette, but soon became the standard for GM muscle cars, modified Jeeps and hot-rods. The first-generation SBCs had a displacement of 265 cubic inches and delivered 180 horsepower. By 1957, the larger version was delivering an astonishing 283 hp--one horsepower for every cubic inch of displacement. As a result, the engine earned the evergreen nickname of "Mouse." To date, more than 90 million have been sold, mostly through GM's popular "Crate Engine" program.

Top Overhaul
To maintain peak performance between major overhauls, most muscle car, Jeep and hot-rod enthusiasts perform a regular "top overhaul" on the SBC engine. This is done by removing and dismantling the cylinder heads, scraping away excess carbon deposits from the top of the pistons and inside the cylinder head combustion chambers, refinishing and polishing inlet and exhaust ports, and finally refacing and lapping the mating faces between the valves and valve seats with grinding paste. The cylinder heads are then re-assembled and bolted back onto the engine block.
Cylinder Head Bolt Tightening Sequence
Standard SBC cast-iron cylinder heads must be tightened onto the engine block in the sequence specified by GM. Cylinder head gaskets are first coated on both sides with a special sealant. The bolts are then inserted and tightened by using moderate torque with a socket wrench. This is done by starting with the central bolt and working outward bolt-by-bolt on either side in the sequence specified in the GM engine manual. This method ensures full contact between the cylinder head gasket and mating faces. It also eliminates the possibility of cylinder-head warpage.
Cylinder Head Bolt Torque Specifications
An adjustable torque wrench fitted with a socket is used during the first torque sequence. The socket is placed over the cylinder-head bolts and tightened until the torque wrench "breaks" and cannot tighten further. This is done at an initial torque wrench setting of 35 to 40 pounds-feet, and by following the sequence laid down in the manual. The torque wrench is then set to between 60 and 70 pounds-feet and the bolts are torqued a second time in the specified sequence. As subsequent bolts are torqued to the higher setting, they relieve some of the pressure imposed on the previously tightened bolt. The bolts are then finally torqued down with the same setting of 60 to 70 pounds-feet to relieve any remaining cylinder head stress. This procedure also ensures that the bolts have been pulled down evenly.