350 Chevy Head Bolt Torque Specifications
by Richard Rowe
Chevrolet's 350-cubic-inch powerplant is the flagship of the company's seminal small-block engine line. The original small-block 350 remained essentially unchanged for nearly 40 years, until the LT came along in 1992. While the LT engine was technically more of an update to the original than a true second-generation motor, the LS that replaced it in 2002 was a true clean-sheet design that shared not a single component with its aged forefather.
Original Small Block
While the first generation 350's 65 ft.-lb. head bolt torque is one of those numbers that all real gearheads have committed to memory, the bolt tightening sequence is a little more complex. Assign each of the three rows of bolts a letter from top (intake manifold side) to bottom (exhaust manifold side); "A" for the top, "B" for the middle and "C" for the bottom. Assign the bolts a number from left to right so that "A1" equals "top row, furthest left" and "C8" equals "bottom row, furthest right." The head bolt tightening sequence is: B3-A3-C5-C4-A2-B4-C6-C3-B2-A4-C7-C2-A1-B5-C8-C1-B1.
LT-Series Engine
All 1995 and earlier LT-series engines use the same head bolt torque (65 ft.-lb.) and tightening sequence as the original small block. GM switched to torque-to-yield (TTY) bolts in 1996, which require a slightly different approach. For TTY bolts, you lubricate the threads, torque the bolt to a specified setting and then turn the bolt a certain number of degrees past that torque setting.
For an LT engine you torque all of the bolts to 22 foot-pounds, then turn the short bolts 67 degrees and the long bolts 80 degrees. Never re-use old TTY bolts, as they permanently stretch when torqued. you could replace them with a set of expensive, new TTY bolts, but a set of standard or aftermarket bolts torqued to 65 foot-pounds will work just as well.
LS-Series
LS-series engines also use TTY bolts, but standard small-block replacement bolts won't work as replacements. If you want to get rid of the LS's TTY bolts, you'll need a set of chrome-moly head studs. The head bolt tightening sequence is: B3-A3-B4-A2-B2-A4-A5-A1-B1-B5-C3-C2-C4-C1-C5. Torquing is a bit tricky if you're using the TTY bolts. For the LS1/LS6, torque all of the fasteners in sequence to 22 ft.-lb. Then, turn all bolts in sequence by 90 degrees. On the next pass, turn all of the bolts in sequence except for those on the front and the rear of the head by 90 degrees. Finally, turn the front and rear bolts by 50 degrees in the proscribed sequence.
For the LS2, torque all of the A and B bolts (the long bolts under the valve cover) to 22 foot-pounds in sequence, then turn all of the A and B bolts 90 degrees in sequence. Make a final pass in sequence and turn them an additional 50 degrees. Next, tighten all of the C bolts (the short ones by the exhaust ports) in sequence to 22 ft.-lb.
References
Writer Bio
Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.
