You see the ads in Hemmings, Old Cars, muscle magazines and newspapers all the time. They are selling engines, transmissions, rear ends, alternators, etc., saying things like "completely rebuilt," "good as new," "every part replaced," etc. The prices are usually pretty attractive, but how can you tell if that piece you want really was rebuilt thoroughly and properly?
That's a good question, and the answer is difficult to explain in a few words. However, we'll attempt to give you some guidelines on checking things out before buying, to help prevent little nightmares and outright fraud.
First, some cautions:
Okay, you know all the pitfalls and danger signs, but you still are tempted to buy that small block Ford or Chevy engine because the price is right and it's freshly painted, and the seller claims it is completely rebuilt. Here's what you want to do to ensure you're not getting screwed:
Take some tools with you when you go look the piece over. All you need is a ratchet wrench, extension, torque wrench, feeler gauge and a few sockets ranging from 3/8ths to 9/16ths in size. Also write down the torque specs for the rod bearing caps and the main bearing caps. Tell the seller you intend to remove the valve covers and the oil pan to look the engine over. If he objects, leave immediately. If he doesn't mind, but is concerned you'll ruin the gaskets, tell him you will pay for new ones ($10) if you don't want the engine.
First remove the valve covers and look at the springs, oil gallery and rockers. If they aren't clean the engine probably isn't rebuilt. If you see sludge, close it up and leave. If things look good, roll the engine over on its side and remove the oil pan. Look for cleanliness and sludge, as before. If everything looks good, remove one set of rod bearing caps and inspect the bearing. It should look smooth and gray if it is new. If you see grooves, uneven polished areas or major wear patterns, the bearings aren't new.
If the bearing looks good, replace the cap and torque it correctly. Test the torque on several other rods, and then test it on one of the main bearing caps. It should be correct, according to the engine specs. If not, especially if the torque is too high, suspect an improper rebuild.
Lastly, check the crankshaft thrust, or end play. Gently wedge a big screwdriver between a crank journal and block casting, levering the crankshaft in one direction. It should move a few thousandths of an inch. Then insert the feeler gauge fingers in the gap until one fits, noting the thickness. The end play (thrust) should be within specifications. If it is too tight or there is no endplay, the engine wasn't rebuilt correctly.
Simple enough, isn't it? These general guidelines also apply for transmissions and rear axles too. Take the time to look at things carefully. It will pay off, because the simple truth of the matter is, if it doesn't look new inside, it probably isn't!