Under What Circumstances Should an Engine Be Overhauled?

[DeArya]

An engine should be sent for a major overhaul if any one of the following three conditions occurs: severe oil consumption without leakage, severe cylinder wear, or abnormal engine noise. 1. Severe oil consumption with blue smoke but no oil leakage. Blue smoke from oil can indicate two scenarios: one might be aging valve stem seals, which only requires replacing the seals without a major overhaul; the other could be excessive clearance between pistons and cylinder walls, necessitating a major overhaul. These two scenarios can be determined using an endoscope. 2. When cylinder wear reaches the overhaul standard, regardless of other symptoms, the decision to overhaul is based on the extent of cylinder wear. If the cylinder's out-of-roundness reaches 0.125mm per 100mm of bore diameter, or if the cylinder's taper wear reaches 0.40mm per 100mm of bore diameter, a major overhaul should be considered upon meeting either condition. 3. Abnormal engine noise. When abnormal engine noise is detected, it can be measured using an engine noise detector. A major overhaul is required in the following two cases: first, if there is severe wear on the connecting rod bearings (small ends) and the crankshaft; second, if there is a cylinder scoring noise, and disassembly reveals severe scoring on the pistons and cylinder walls.