The Sportster is a line of Harley-Davidson motorcycles first produced in 1957. According to enthusiasts Allan Girdler et al., this makes it arguably the longest lasting model in motorcycle history. Mechanic Joe Minton warns that over-tightened bolts are likely to fail eventually, which is why it makes good sense to know the recommended torque specifications and to employ a torque wrench.
For many Sportster fans, the famous 42 foot-pounds of torque needed to tighten the cylinder bolt is a figure seared into the imagination from an early age. Minton explains that Harley-Davidson spent a great deal of time arriving at this particular figure. He recommends that if you want more torque, you should hone the cylinders and tighten the torque plate bolts to the same specification.
Harley's head-bolt torque method hearkens back to a time when torque specifications were less scientific. Minton explains that the procedure requires the use of a torque wrench but not for final tightening. First, you should pre-load the bolts to about 16 foot-pounds. Then, with a pencil, make a witness mark on both the cylinder head and head bolt. Then turn the head bolt an extra quarter-turn to achieve the correct torque.
With specific reference to the XL Sportster 2004 to 2006, Clymer, the renowned repair manual specialists, recommend that cylinder head bracket mounting bolts are tightened between 17 and 24 foot-pounds. Rocker arm shaft bolts should be tightened from 18 to 22 foot-pounds. For hex bolts and socket head bolts, a figure of 135 to 155 inch-pounds is specified.
General Torque Specifications
According to Clymer, SAE 2 grade bolts, as specified by the Society of Automotive Engineers, should be tightened as follows: A 1/4-inch bolt should be tightened to 6 foot-pounds. A 5/16-inch bolt should be tightened to 12 foot-pounds. For a 3/8-inch bolt, set your torque wrench to 20 foot-pounds. A 7/16-inch bolt should be tightened to 32 foot-pounds and a 1/2-inch bolt to 47 foot-pounds. Tighten a 9/16-inch bolt to 69 foot-pounds. A 5/8-inch bolt should be tightened to 96 foot-pounds. A 3/4-inch bolt should be tightened to 155 foot-pounds. Set your torque wrench to 206 foot-pounds for a 7/8-inch bolt. A 1-inch bolt should be tightened to 310 foot-pounds.