Rods are attached to pistons with a single extension of the rod through the piston (see Figure 300-18), or with multiple through-bolts as shown in Figure 300-20. The advantages of multiple bolts are:
1. The smaller bolts are much easier to accurately tension.
2. Adequate pre-stress levels are reliably maintained.
3. Loading by the bolts is more evenly distributed in the piston.
This feature is especially useful for large diameter aluminum pistons with large diameter rods. Such pistons with the single through-bolt attachment sometimes have nut-loosening problems after a number of temperature cycles. Factors contributing to this looseness are the difficulty of properly torquing one large nut, and possible non-squareness of the nut’s face with the piston surface.