A connecting rod is an engine component that transfers motion from the piston to the crankshaft.

Connecting rods are commonly made from cast aluminum alloy.  As a result, are designed to withstand dynamic stresses from combustion and piston movement.

The small end of the connecting rod connects to the piston with a piston pin.

So, The piston pin, or wrist pin, provides a pivot point between the piston and connecting rods. Spring clips, or piston pin locks, are used to hold the piston pin in place. They can also be a press fit in the rod as well.

The big end of the connecting rod connects to the crankpin journal to provide a pivot point on the crankshaft. Connecting rods are produces as one piece or two-piece components. A rod cap is the removable section of a two-piece connecting rod. As a result, The rod cap is attached to the connecting rod with two cap screws for installation and removal from the crankshaft.

Some Of The Main Causes Of Failure Are;

  • Fatigue
  • Pin Failure
  • Over Revving
  • Hydrolock
  • Over Loading
  • Rod Bearing Failure
  • Pin Bushing Failure

So, One of the first things you should always do inspect each and every connecting rod. Check for any obvious surface nicks, burrs, scratches or other damage that might create stress points. If grinding is needed to debur or clean up a casting, do so lengthwise on the rod, never sideways.

Steel rods should always be Magnafluxed to check for cracks. Use penetrating dye to check aluminum rods.

Rods (including brand new ones) should also be checked for dimensional accuracy. Measure the I.D. of the big and small end bores. Measure the rod’s overall length. Check the rod for straightness. Any bending or twisting between the big end rod bore and the wrist pin bore needs to be corrected.

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Connecting Rods
Connecting Rods

The connecting rod small-end bearing is more difficult to lubricate effectively because of its oscillating, rather than rotating, motion. A floating wrist pin needs an oil film to be quickly formed and maintained during cold starting.

Also critical to connecting rod longevity is checking and double-checking rod bearing clearances and wrist pin fit. Too tight or too loose can cause major problems at either end of the rod. Also, make sure rod bearings have the proper crush fit. The backs of the rod bearings should be installed dry, while the face of the bearings are coated with assembly lube.

Installing the rod bolts correctly is essential to preventing rod failures.