Weight and Balance

The ride over on the ferry this morning was beautiful and makes me appreciate living in the Pacific Northwest.

One major task that needed to be completed was to weigh and then try to balance as close as possible opposing connecting rods, pistons, wrist pins, rings and any other accessory parts that would be moving with the pistons.  The Lycoming IO 540 engine has 6 cylinders that are horizontally opposed with three on each side.  Opposing cylinders are 1 and 2, 3 and 4, 5 and 6. The connecting rods had come back from being refurbished and weigh within 5 grams of each other.  The goals in the end was to have opposing assemblies be at 4 grams or less to get the smoothest running engine possible.  I was certain that I could decrease that value.

All parts of the piston assembly were weighed separately and identified so they could be mixed and matched.  The only given was that each connecting rod had already been assigned to a specific cylinder so I had to worked around that.

I used a simple triple beam balance that would weigh down to 0.10 grams.

I weighed everything and assigned a number to each and then made a chart to cross reference the weights.

The piston pins and plugs where basically all identical, but there was variation in the pitons, connecting rods and rings.  In the end I was able to get the total variance between opposing cylinders down to 1.15 grams.

All of the piston assemblies and connecting rods that had been balanced awaiting installation.