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 Connecting Rod Balancing

Balancing my pistons was pretty straight forward.  All I had to do was install the rings and place the pistons on my digital scale.  But balancing the rod ends proved to be quite difficult.  I could not manage to get the rod placed back on the scale in exactly the same spot every time.  Sometimes I had as much as a 50g difference between one placing to another.  Every jig I made was either not accurate enough,  added friction resulting in uneven support,  or added loads to the rods which resulted in erroneous readings.

I posted a message to the CorvAIRCRAFT e-mail list,  and I shortly had my answer.



Don McGehee sent me a private e-mail with this attached drawing of a jig which was drawn from memory of one he saw in a hot rod engine shop.

From his drawing,  I made this jig.

I turned 2 phenolic disks which slide freely over a   shaft,  which lowers friction and allows me to change the disks from one shaft to the other,  for balancing each rod end.

Although the centers of the shafts are the correct distance apart,  the chain all but eliminates any unwanted side loads.

I've been able to remove and replace the connecting rod on this jig,  and if it's not exactly the same weight when I make the change,  it's only 1g difference.



One good thing I've found out from this exercise is that the stock connecting rods are very close anyhow.  From my heaviest to my lightest,  there's only a 7g difference.

If you have comments or suggestions, E-Mail me, Patrick Panzera