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Chevrolet BBC rods from the factory sometimes the mating surface is not 90 degrees to the sides, which will cause taper when the mating surfaces are cut.
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I agree many rods, not just BBC, don't have the housing bore and sides perpendicular to the parting line. My personal opinion is that we often find rods (especially OEM) that also don't have the sides parallel to each other. If that is the case then one side will be closer to "square" than the other.
We understand that we will hone, more or less, perpendicular to the rod sides. The cap cutter should cut the parting line perpendicular to the sides. Therefore we need to prepare the sides, to the best of our ability, before we cut the parting surfaces. Then we need to check the parting surfaces before we cut them. How did we remove the pressed in bolts? Did we twist the forks doing that? Are there burrs or dings anywhere?
Only then do we begin to cut the parting surfaces. Production "guys" will touch off on one rod,or cap, dial in the amount they want to remove, and make their cuts.
I prefer to touch off every rod and cap, every time, and observe the cut surface to see if it's cutting "flat". If not, I turn the part around to square off the other side and touch it again. I pick the best side and cut the amount I prefer.
Then we get to prep our newly machined surfaces. Reinstall the press in rod bolts, again trying not to twist the forks. Reinstall the cap(s), torque the bolts using a procedure we can repeat on final assembly. And make sure the sides are flat so that the rods don't "rock" as we hold the pair on the hone.
After that, it's up to the hone operator to do his job. The prep work is "just machining", the honing is where the "touch" comes into play.
All in all, it's not easy, or cheap, to do the job right.
Then if we want to have "fun" let's do some rods that the need to be "saved". You know....the blue ones.