SECRETS OF ENGINE BALANCE—continued.

of the rim in relation to the register fitting over the flange on the crankshaft. This goes to show the importance of extending the balancing operations beyond the crankshaft and therefore I will proceed to explain the method adopted in the Laystall Works for dealing with connecting rods and pistons. Before doing so, I would mention that unless one uses a special form of machine for the purpose, there is little chance of securing accurate results and the primitive methods of suspending a rod from one end and weighing the other, or supporting one end on Vee Blocks, for the same purpose, can only give, very rough approximations to correct balance. True they are better than nothing, but are not good enough for the racing or Competition motorist for whom nothing short of the best will give satisfaction.

How Connecting Rods are Balanced.

One of the most interesting features concerning engine balance is to be found when dealing with connecting rods, for part of the rod must be regarded as a revolving mass and the remainder as a reciprocating mass.

In rods of normal design, the big-end and a third of the length of the rod may be taken as a revolving mass, and the remainder as a reciprocating mass, and this is taken into account during the balancing operations. As may be seen in the accompanying photograph, the rods are first suspended from the big and small ends respectively by means of knife edge mandrels and then the balance arms on either side of the machine are set to the zero position. The whole set of rods is then tested until the lightest one is found, so that small masses of metal can be removed from the others to make them all of equal weight. The arrangement of

the machine permits accurate comparisons of the weight of both the big and small ends of the rods, and one can work down to half a dram with absolute accuracy.

Having secured the correct balance and equalisation of weight in respect of the four rods, the next thing is to fit the pistons and repeat the process, thus ensuring that the pistons will be balanced as accurately as the rods.

When to Balance an Engine.

As a final remark I may mention the need for leaving all balancing operations until the last thing after an engine has been overhauled, for even in removing metal during the process of adjusting bearings it is an easy matter to disturb the balance, whereas a heavy washer fitted to one of the connecting rod bolts will have a similar effect. Correct balancing means more power, greater acceleration and decreased wear on a high speed engine ; but is nevertheless the most neglected of all engine overhaul operations.