GEN III VS. GEN IV CONNECTING RODS
The early Gen-3 press-fit connecting rod was replaced by the Gen-4 free-floating piston pin with rod bushings. Some shops try to upgrade Gen-3 engines by substituting Gen-4 pistons, and keeping the earlier rods. You need to be aware to USE the Gen-4 retaining clips. The old press-fit rods become free-floating (although metal to metal) when using the newer pistons & pins. We’ve had a couple customers that assumed they were the same size because they “Mic pretty close.” GM reduced the Piston Pin diameter from .945 to .943. When using a later model (smaller) piston pin, it will actually slide in the pin end (assuming the rod is still in original spec). I’ve tried OVER 100 by hand, they can be stubborn to go in at first, which would lead some to believe it’s “still a press-fit rod,” but it’s just from normal oil and carbon build-up, as well as the near-perfect angle at which you have to insert a free- floating pin before it will go in. With a little patience and a bit of a clean-up, they slide right through almost every time. Simply put, when upgrading Gen-3 rods with Gen-4 pistons, if you don’t use their retaining clips, the piston pins will slide out into the cylinder walls….very costly!
Miles Rogers
BP Rods
Magnolia, TX
October, 2017
