Connecting Rods

1. Connecting Rods

2. Materials • Cast iron • Forged steel – most common • Aluminum – not for street use • Titanium • Plastic • Powdered metal (PM)

3. Powdered Metal Rods • Powdered metal rods are relatively strong, stable, and economical to produce. • Powdered metal rods are made, in their final shape, from powdered metal which is pressed and heated until it fuses into a solid form. • Powdered metal rods use a cracked cap design, which require special repair procedures.

4. Connecting Rod Design • The connecting rod moves in both a rotating (big end) and reciprocating (small end) motion • The connecting rod is designed to be as light as possible, but still have the required strength needed • Under normal cylinder pressures a connecting rod has to transmit as much as 10,000 pounds of force from the piston to the crankshaft

5. Connecting Rod Small End Design • Non-floating (pressed pin) • Piston pin is held to the connecting rod by an interference fit • Pin must be pressed out, and rod must be heated to install new piston and pin • Floating • Piston pin and small end of the rod have an oil clearance • Connecting rod must be drilled for pin oiling • Retaining clips in piston keep the pin from falling out

6. Connecting Rod Inspection • Big end • Size • Taper • Out-of-round • Surface finish • Small end • Size • Surface finish • Straightness

7. Connecting Rod Length • Connecting rod length is measured from the centerline of the big end to the centerline of the small end

8. Rod Angularity • Rod ratio = Rod CL to CL length Stroke • Less rod angularity (higher number) creates less cylinder side loading • Less rod angularity benefits high rpm operation the most • Long rods or short stroke = Less angularity

9. Connecting Rod Preparation • Remove casting flash and burs • Polish along the length of the rod not across it • Magnaflux • Check length • Replace rod bolts