If the rod is bent, then at TDC the piston will be at a lower point in the cylinder. The swept volume of the piston will still be the same, but the volume at the top of the compression stroke will be larger, meaning that cylinder has a lower compression ratio. Lower compression ratio = lower compression.
At least, that's the logical interpretation... there could be other factors I'm not aware of
It could indicate the rod is bent but it could also indicate several other problems. I would think if a rod is bent enough to limit piston travel the piston would also be damaged. You could have a damaged piston and the rod could be either good or bad.
I don't think a compression tester is the best way to check for a bent rod, there are too many other factors that can affect compression readings.
Clifton
