How to Determine if the Piston is Installed Backwards
2 Answers
Judging by the most obvious indicator, the arrow mark should normally point towards the exhaust valve during proper installation. There are also English letters "IN" and "EX" on the top of the piston. "IN" should be installed near the intake valve, and "EX" should be installed near the exhaust valve.
In my years of experience repairing cars, determining whether a piston is installed backwards requires careful attention to detail. There is usually an arrow mark on the top of the piston pointing toward the front of the engine. If there is no arrow, check the size of the valve pockets—the intake valve pocket is larger and should face the intake manifold side. The pin hole position is also asymmetrical, designed with an offset to reduce noise and wear. If installed backward, the engine will produce knocking or abnormal noises after starting, and fuel consumption will increase significantly. Once, I took on a job where the customer complained about lack of power and black smoke. After disassembling the engine, I found the piston was installed backward, causing the piston rings to seize. To avoid such misalignment, I recommend marking the top of the piston or taking photos to document its position before disassembly, and never start the engine after casually reinstalling it.
