What are the causes of piston slap after an engine overhaul?
3 Answers
Engine overhaul after the production of piston slap causes are: piston and cylinder with excessive clearance, piston direction installed in reverse or piston deformation, cylinder wall lubrication is poor, lubrication conditions are poor, oil pressure is low or oil viscosity is too low, connecting rod bending or twisting deformation, piston connecting rod group assembly makes the piston in the cylinder tilt exceeds the allowable range, etc. The specific causes of piston slap after an engine overhaul are as follows: 1. Due to improper repair, the piston and cylinder fit clearance is too large, or because the cylinder wear is serious, the clearance is too large, the engine at low temperature when the piston clearance is large, the piston slap noise is serious, the engine temperature rises after the piston expansion, making the piston fit clearance smaller, the piston slap noise is reduced or disappeared. 2. The piston direction is installed in reverse or the piston is deformed, destroying the normal clearance between the piston and the cylinder, resulting in piston slap noise. 3. The cylinder wall lubrication is poor, the lubrication conditions are poor, the oil pressure is low or the oil viscosity is too low, the piston and the cylinder wall can not form a normal oil film, the piston and the cylinder directly collide and produce piston slap. 4. The connecting rod is bent or twisted and deformed, and the assembly of the piston connecting rod group causes the piston to tilt in the cylinder beyond the allowable range. Not only does it make the sealing worse and the lubrication conditions worse, but it also causes abnormal wear of the cylinder, which causes the piston and the cylinder wall to collide and produce noise.
Engine knocking after overhaul is a common issue I've encountered. The most frequent cause is assembly errors, such as improperly installed piston rings or excessive clearance between pistons and cylinder walls, which leads to piston-to-wall contact during operation. Insufficient lubrication is another major factor – low oil level or clogged oil passages increase component friction and cause knocking. Misaligned connecting rods can also create uneven forces and vibration during operation. Early combustion problems may amplify knocking sounds too. My advice is to first verify assembly precision post-overhaul and have a professional mechanic perform adjustments immediately to prevent minor issues from escalating. For prevention, regular oil and clearance checks help mitigate risks – after all, the engine's core components deserve proper care.
My car just had a major engine overhaul, and after driving for a few days, I heard a knocking sound similar to a ticking noise, which startled me. I took it to the repair shop for inspection, and they found that the piston rings were misaligned, and there was also a slight issue with the oil pump, causing uneven lubrication. The mechanic said that minor scratches on the cylinder walls were also related, which are often overlooked during major repairs. Another possibility is that the clearance wasn't adjusted properly during assembly, making the abnormal noise more noticeable during cold starts. If you encounter a similar issue, don't delay—first check the oil pressure, then inspect the assembly precision. Spending some time on early repairs can save you a lot of money. Pay attention to changes in engine sounds during routine maintenance; small details matter a lot.
