Connecting rods

Connecting rod rebuilding is one of the most popular types of engine repairs. Connecting rods transfer a major force from the working pistons to the crankshaft. Because of being subjected to such heavy loads, they often wear out. In many cases, rebuilding is sufficient instead of replacing it with a new one. We can rebuild the small end as well as the big end of connecting rods. Due to the extraordinary precision of connecting rod design, such rebuilding requires a lot of knowledge and the use of high-quality tools and machines. This is the only way to guarantee that they meet the manufacturer’s strict requirements. It is essential to maintain the accuracy of the holes in the connecting rod. The newer the engine, the greater the dimensional precision that is required for these components.

Connecting rods are made of highly durable carbon steel, but are nonetheless exposed to damage that requires immediate repair. Rebuilding the connecting rods may become necessary if the oil has not been changed regularly. Used oil is often contaminated with particles of abrasive metal. These small parts act as an abrasive and cause faster wear of various surfaces by forming numerous scratches and microdamage. This can block the operation of the crankshaft bearings. Rebuilding the connecting rods may be necessary when they have been exposed to too high temperatures. Such conditions can lead to pitting on the connecting rod bearing surfaces or even to their cracking.

The connecting rod big end is subjected to inertial loads caused by the motion of the piston and the connecting rod itself. This process results in the big-end deformation, also called ovalisation. Even a slight deformation can result in shaft jamming and faster wear and tear. If the connecting rod shape differs significantly from the specified shape, there can be problems in starting the engine. In the event of a failure (ovalisation), the connecting rod is remachined using a honing machine from Sunnen, an American company. We can machine connecting rods to the required catalogue size while maintaining the perpendicularity of the holes to the connecting rod stem.

The last step of connecting rod rebuilding is the repair of the small end. Large play between the pin and the bearing surface in the connecting rod can eliminated by bushing replacement followed by reboring. By using a Sunnen connecting rod boring machine we are able to obtain the appropriate play between the bushing and the small-end pin while maintaining the perpendicularity of the connecting rod and the same length of the connecting rod set. Otherwise, even minimal unevenness may cause uneven wear of the piston walls and cylinder bearing surface, noisy operation of the crank set and even the dislocation of various bushes.

A very important parameter of a connecting rods is its weight. A set of connecting rods should be in the same weight group. We measure the weight of the connecting rod at each end using an instrument combined with precision scales. Any differences in connecting rod weights should be adjusted by removing unnecessary material.