Repairing a machine is generally a two-stage process. First you need to figure out which part is actually the faulty one, and secondly you need to consider which other parts may also need replacement. So, if you replaced a spare part, but the problem was not resolved or a new problem came up, this does not necessarily mean that it was defective. Here are some examples:
- Your machine suffers from low compression, and you figure out that the piston ring has worn out. Disassembling the engine to replace the piston ring, the gaskets around the cylinder may not be reusable. So, if these are not replaced, the problem may persist, or other problem may come up.
- You replaced the carburetor, but the machine does not still start. As a result, the faulty part may be actually the ignition coil, and not the carburetor.
- After you replaced the piston, the machine worked for a couple of minutes, only. You disassembled the engine again and found signs on the piston indicating overheat from the side of the muffler. In this case a small bit of metal might enter the cylinder from the rusty muffler.