The engine in your old car has reached the end of its lifespan, but the car itself is in good condition, so you decide you will rebuild the motor instead of completely replacing it. A basic rebuild job involves replacing the primary operating parts of the engine, and sometimes you can find used parts at a junkyard to use for the project to save even more money. However, there are certain engine parts that should always be bought new during a rebuild. Here is a look at some of the parts that you should not pick up used even though new parts will be more expensive. 

Pistons and Piston Rods

While an engine is in operation, the pistons move back and forth in the cylinders to cause combustion repeatedly. If the pistons are not in good shape or if the rods that support the back-and-forth action are bent, the combustion action that is necessary to keep the engine going will not happen as it should. Unfortunately, pistons and piston rods can sustain wear with regular use, especially in an engine that is not well-maintained. Therefore, it is best that you do not invest in either used pistons or piston rods. 

Valves

The valves in an engine regulate the flow of fuel and air as well as acting as exhaust outlets after combustion occurs. If the valves are not opening and closing as they should, proper engine combustion inside the cylinders will not happen, which will leave the engine sputtering and dying instead of running at a steady idle. If you buy used valves, there is a good chance you will invest in problems that were already present in the vehicle the valves came from. If the owner of the engine frequently left their oil unchanged, it can cause debris buildup inside the valves that prevents them from opening and closing as they should, for example. 

Crankshaft 

The crankshaft turns to continuously move the piston rods in their back-and-forth motion to push the pistons into the cylinders and cause combustion. If the crankshaft is not turning at a smooth pace, it will prevent the engine from running because all actions need to happen in a stable and reliable way. If you buy a used crankshaft, you could end up with a lot of problems if the crankshaft does not operate as smoothly as it should. Because this is a primary engine component, it can be an expensive investment to buy a crankshaft new, but it is well worth the price. 

For more information on purchasing engine parts, contact a company like Dean's Auto Repair Inc.