A system and method enable monitoring of a mechanical condition of a reciprocating compressor. The compressor includes a compressor frame, a pressure chamber, and a pressure head. A plurality of tie bolts are secured between the compressor frame and the pressure chamber head. A sensor assembly is secured to one of the plurality of tie bolts. The sensor assembly includes an elongation member positioned to extend in concert with extension of one of the tie bolts. A sensor measures extension of the elongation member to thereby monitor cylinder pressure.