First look at the large end of the connecting rods to see if they were numbered at the factory. Mixing them up is not serious because they should all be the same and there are no parts that wear together. Most newer engines use the "cracked cap" design. Look at the mating surfaces of the connecting rods and caps. With the cracked cap design, those surfaces will not be machined smooth and shiny. The rod is cast as one piece, the large hole is machined, then it is forcibly cracked to make it into two parts. The cap will only fit one way, and they are not interchangeable. Since they can't be machined, they can't be resized either. If the diameter is too large it has to be replaced.
The valves can be moved around too. It's when you start machining them that you'll want to keep them matched to the holes they're being machined to.
The biggest issue is the lifters and camshaft. Those wear together and must be kept in the right order. The engine will run okay if they're mixed up but if excessive wear develops you'll want to replace the camshaft and lifters. It's not uncommon to replace those parts anyway during a rebuild because they are wear items. In engines that use push rods those wear too to match the lifters and rocker arms but it's not as serious if you mix them up. On engines that use lash adjusters in the tips of the rocker arms, those rocker arms must be kept with their mating lobes on the camshaft. You'd like to keep the lash adjusters matched with the valves they were pushing on, but if they get mixed up they will usually still be okay.
Wednesday, June 5th, 2013 AT 11:38 PM