Small End Bearing

The small end bush is made of phosphor bronze and there is very little maintenance that can be undertaken. If it is worn, it must be pressed out of the con-rod and a new bearing pressed into place, where it can be reamed to the correct size.

Replacement

The old small end bush needs to be pressed out of the connecting-rod and to do this a tool should be made from steel bar which is smaller in diameter than the bush and has a spigot turned at one end to fit inside the bush. You will also need a piece of tube with a hole lager than the bush to push the old bush into while supplying support to the connecting-rod. Place the assembly into a vice and press the bush out. 

I like the design of the BSA tool as it provides a smooth pressure from the thread and nut, rather than the impact of a hammer.

BSA Tool

Next line up the oil hole of the new bush and the hole in the con-rod. Now carefully press the bush into place with the tool as shown in the diagram, until it is flush with the rod.

You will now have to ream the bush to match the gudgeon pin. Care must be taken to ensure that the reamer is square to the con-rod. Clean any residue from the bush before assembling with the piston.

Remember to liberally oil the bush on assembly.

Adjustable Reamers

The blades of an adjustable reamer are separate from the body and are fitted into grooves in the threaded shank of the tool. Adjusting nuts located below and above the blades control the diameter of the reamer. The reamers come with straight or spiral flutes, with or without a floating pilot on solid mandrels, and in several sizes. They are used to enlarge drilled holes to an exact true size using a series of small cuts rather than one large cut.