Tuning cars will eventually come to a day when at some point during your ownership the engine will be left with it's tongue hanging out. hehe when that day comes, you'll be faced with the decision to replace or rebuild. Replacing the tired engine with a brand new one might be the simplest, yet will def be the most expensive. Swapping in a used engine is a popular choice, as it's usually the the most economical alternative and the simplest to accomplish. However your rolling the dice with this option and hoping your not picking up where the dude b4 left off--a few beatings shy of your previous engine. That leaves engine rebuilding, and to unexperienced carcrafters can be a situation not thought about.
First off, research is the key. It may sound like homework, but it'd be wise to hit the books/internet b4 turning the first wrench. You may already know your way around a toolbox and have been tinkering with your car for quite some time, however there are many small details involved in the complete teardown and assembly of any specific engine that you may not be aware of. Research the engine beyond it's manufacturer and engine family, down to it's model, year, displacement, power rating, and any other specs particular to that engine(forced induction etc.). Don't rely solely on generalized repair manuals for all the info.
B4 rebuilding u are going to need something to rebuild, most likely the engine that came in your car. though if the engine experienced some major catastrophic failure, all its crtical parts should be checked by a competent machine shop b4 proceeding. Damage isn't always detectable to the naked eye. EX: damaged cylinder bores can be sleeved, casting cracks can be welded or drilled and pinned, stripped threads can be re-tapped or repaired with inserts, cam bores can be sleeved and so on....
PICKING A MACHINE SHOP
many tunerz seem to place more emphasis on engine assembly than the machining process. The machining stage can be the make or break of rebuilding an engine. Youe best bet is to approach a machine shop known locally for high performance street and racing machines(consantines). If your intimidated by approaching experienced race engine builders for your first project, keep in mind that thet still have to rebuild truck and car engines and like to keep the workflow going and your engine won't be beneath them.
THE DROP OFF
You could probably drop off a complete engine, but dismantling the core will save you time and money. The best approach would involve completly dismantling the engine and keep and label the old parts. Crank should be removed from the block(handle carfeully, journals are very vulnerable) to prevent warping, crankshafts should be stored by standing them on end. retain old bearings and keep everything in the same position.
It's common knowledge to anyone who's working on engines that the rotating internals need to be balanced. The reason engine builders offer spin balance procedures as optional at machine shops is because a basic rebuild often consists of an original crank and connecting rods with a net set of pistons. Piston sets are weight matched(quality sets) and the difference in weight between stock and replacements is often slight enough that rebalance is not nessecary. When diff pistons and rods are substiuted, rebalancing becomes critical and a MUST in stroker engines.
A goos machinist can provide you with pertinent info upon returning the refurbished parts. Of note are the various oil and coolant passage plugs removed by the machine shop. Most good shops provide fresh plugs but may not install them unless asked. After getting the parts back everything should be cleaned thoroughly before assembly actually begins. (basic soapy solution-liquid dish soap, hot water is preferred, and a set of engine cleaning brushes allow for a good cleaning) Once the cleaning is complete, blow dry the block with compressed air and wipe down with clean rags. (if u don't intend to assemble right away, wipe down all machined surfaces with engine oil and coat the rest with a light spray of WD-40) Keep this in mind l8ter when it comes time to paint the engine, which will have to be degreased with solvent.
By now the block should be cleaned, dried, and mounted on a suitable stand. All fastners to be used should have also been completely cleaned, and all threads free of burs. Have quality assembly lube on hand. If the machine shop has done a good job there should be no concerns over bearing clearance, but it's always a good idea to check (micrometers) (some other useful tools will include a torque wrench, ring compressor, and possibly a harmonic-balancer installer). Use plenty of lube on the bearings and make sure that all fastners that don't require sealant are coated with a few drops of oil on threads and under shoulders. Dry threads can create inaccurate torque readings. Piston rings should also be treated with a thin coat of oil b4 installing on the pistons, and the rod bolts should be covered - a short peice of rubber hose works-to ensure that they dont scratch the crank during installation. Continue to spin-test the rotating assembly after torquing each rod to make sure there is no binding. Check main and rod bearing clearances, crank endplay, and rod side clearance as specified by the manufacturer. Crankshaft end seals(rear main and timing cover) should also be coated with engine oil. when time to install the cylinder head(s) make sure to follow the torque sequence listed in the factory manual. Intake manifolds usually have a prescribed sequence as well. procedures for valve adjustment should be found in your source books..
Hopefully this helps with some misc things to know and understand when rebuilding an engine.
1997 Eagle Talon TSi - 11.3 @ 126MPH
1989 Colt Turbo - 198WHP 202 Torque - RIP
1991 Colt Turbo Conversion Targa Rally Car - Work in Progress