The Balance Issue
It's common knowledge to anyone who's worked on engines that the rotating internals need to be balanced. What isn't always so clear is why and when engines must be rebalanced during the rebuilding process. Engine builders typically offer spin-balancing as an option, which may seem confusing since the internal balance of the rotating assembly is considered critical. In truth, most factory-balanced engines aren't spot-on, and you'd be surprised to see just how far out of balance some stock crank/rod/piston assemblies are when placed on a dynamic balancing machine. The original manufacturers often allow a broad margin of tolerance in this area, as most passenger-car engines don't rev very high or for very long.
The reason the spin-balance procedure is considered optional in many shops is because a basic rebuild often consists of an original crankshaft and connecting rods with a new set of pistons. The pistons in most quality piston sets are weight-matched, and the difference in weight between the originals and the stock-type replacements is often slight enough that a rebalance is not absolutely necessary. When significantly different pistons or connecting rods are substituted, rebalancing becomes more critical. For stroker engines, it's mandatory.
The spin-balancing procedure is labor-intensive and therefore not cheap. Figure on somewhere between $150-300 for this service. However, even if you're only swapping in a set of replacement slugs, spend the extra cash if you can swing it. The balance job provides peace of mind and usually a noticeable improvement in engine operating smoothness. The lack of imbalance will also be easier on the internal components over the long haul.
As previously mentioned, Dougan's recommended that our rotating assembly be spin-balanced. This was primarily due to the change of piston and rod design, which seemed to indicate a significant change in the weight of these components. After the balancing procedure had been performed, it was clear we'd made the right decision, as the new piston/rod assemblies definitely didn't jibe with our stock crank. This was easily corrected by strategically drilling the crank counterweights to remove material in a few specific areas.
Your role in the project will be limited to decision making while the core components are in the machine shop, but once you get them back, it's time for hands-on participation. Here again, a good machinist can provide you with any pertinent information upon returning the refurbished parts. Of note are the various oil and coolant-passage plugs that have been removed by the machine shop. Most good shops provide fresh plugs with the completed job, but may not install them unless you ask. If you have a rapport with the machinist, ask him to show you how to install them. Part of the challenge is knowing where they all go (refer to those source books again), as well as how to properly install them so they stay put. If you're unsure and can't get assistance, pay the extra few dollars to have the shop install the plugs, and verify when you pick up the block that it's ready for assembly.
After getting the parts back, everything should be thoroughly cleaned before assembly actually begins. Most builders recommend a basic soapy water solution-liquid dish soap works well. Hot water is preferred if available, and though many will simply blast the block with a hose, a set of engine cleaning brushes allows more thorough cleansing.
Once the cleaning is complete, blow the block dry with compressed air (if available), or wipe it down with clean rags. If you don't intend to begin the assembly right away, wipe down all the machined surfaces, like the cylinder and lifter bores, with engine oil, and coat the rest with a light spray lube like WD-40. Keep this in mind later when it comes time to paint the engine, which will have to be degreased with solvent. If the block and parts will be stored prior to assembly, seal them in plastic bags after coating them with oil.
After collecting our stuff from Dougan's, we blasted the block with the hose, then doused it with hot, soapy water and began scrubbing using the various brushes included in the cleaning kit we picked up. The brushes allow for cleaning threaded holes and other tight areas where dirt and metal filings can hide, waiting to come out after the engine is started and the oil is flowing, only to ruin the fresh rebuild. After the block was cleaned and dried, we immediately rolled it into the shop to begin the assembly.