Wrist Pin Bushings

Is the wrist pin knocking in the small end of the connecting rod, or does an engine need rebuilding with new bearing surfaces? The bushings in this category replace the worn surface between wrist pin and connecting rod and are for you if you are rebuilding or building up an engine, from car to tractor and industrial engines.

What the bushing in the small end of the connecting rod does

The bushing is pressed into the small end of the connecting rod and forms the bearing surface for the wrist pin. It must withstand alternating loads from combustion while maintaining a thin oil film. When the bushing wears, play and a knocking noise can develop, and wear can typically progress faster if lubrication is insufficient. The bushings are used when reconditioning existing connecting rods or in projects where the wrist pin and connecting rod need to be matched to each other.

How to choose the right bushing

The starting point is the engine and the parts the bushing must fit. At Clevite and ACL, for example, many bushings are listed for specific engines, while CP Pistons states dimensions in the product name, e.g. 974 x 900 x 1060. Always check the product description to see what the dimensions refer to. Look at:

• outside diameter relative to the bore in the connecting rod and the required press fit
• inside diameter relative to the wrist pin, and whether the bushing needs to be machined to size
• width and shape, e.g. tapered bushings with wide taper
• position of the oil holes

Installation and fitting

The bushing is typically pressed in and then often needs to be reamed or honed to the final clearance specified by the engine or piston manufacturer. The oil hole must line up with the hole in the connecting rod, otherwise the bushing may be starved of oil. The job requires precise measuring tools, so have a workshop do it if you don't have the equipment yourself. Superpro and ARB are also among the brands in the category.

Frequently asked questions

Does a new bushing need machining after installation?

Often, yes. When the bushing is pressed in, the inside diameter can change, so it typically needs to be reamed or honed to the clearance specified for the wrist pin by the engine or piston manufacturer.

How do I know if the wrist pin bushing is worn?

The play between wrist pin and bushing can be measured with measuring tools once the connecting rod is removed. A knocking noise can be a sign, but can also have other causes, so always measure before replacing.

What do the numbers in the name of the CP Pistons bushings mean?

The numbers, e.g. 880 x 700 x 1000, indicate the bushing's dimensions. Check the product description to see which number corresponds to outside diameter, inside diameter and length, and compare with your connecting rod and wrist pin.