Originally Posted by mmurray24
Rebuilding a 327 out of a 1968 Chevy Camaro. The engine was dismantled without the pistons being numbered so it is unsure what cylinders they should be put back into. The blocked was honed the pistons were cleaned and have new rings. Can the pistons be put back in at random? If not what are the potential problems that can occur?
Problem is more with rods than pistons though that isn't clean by any means but incorrectly placed rods will make a disaster on the crankshaft. There are several conditions that need to be satisfied at the same time.
1) Looking at the big end of the rods you will see a chamfer where the cheek and bearing bore meet, there will be a larger chamfer on one side than the other. This always faces to the outside of the rod journal so that the pair of rods has the small chamfers facing each other when assembled on their journal. Done backwards the rod will bind on the journal ends and with the crank become damaged.
2) The piston should have a notch or arrow that indicates facing forward toward the waterpump end of the block. This needs also to be correct to and with the rod installed correctly with the chamfers as outlined previously. The notch or arrow indicates the direction needed for the wrist pin offset. The pin is not centered in the piston but off set to keep the thrust side skirt pushed against the cylinder wall. If the piston is inserted backwards the offset will cause the piston skirt to snap over from the non thrust side to the thrust side with every revolution of the crank. It doesn't take much of this before skirts break off the pistons.
3) Not out of the woods yet. The rod caps are unique to each rod hopefully these aren't mixed up. For installation of the cap to the shank there is a relief for the tang of the bearing inset to mount into, not only must the tangs be in this relief but when cap is installed on the rod shank they must face each other. Then as the piston arrow and rod chamfer are correct so the insert tang relief needs to face out of the block toward you looking from the pan rail side.
So you've got three major things that have to come together at the same time for each and every rod/piston assembly. After that you can worry about getting the right piston back in the right cylinder if that is even possible given the unknowns and constraints.