Pistons
Pistons are the cylindrical components that move up and down inside the engine bores, transferring the force of combustion to the crankshaft through the connecting rods.
What it does
Combustion pressure above the piston drives it down the bore. The connecting rod converts that linear motion into rotation at the crankshaft. Piston rings seal combustion pressure and control oil on the bore wall.
Signs a piston set is failing
- Blue exhaust smoke, indicating oil passing the rings
- Loss of compression on one or more cylinders
- A knocking noise that is loudest under load
- Excessive oil consumption with no external leak
When to replace them
Not a wear item in normal service. Replaced during a rebuild, after overheating damage, or following ring or bore wear.
What to confirm before ordering
Have these ready and the counter can usually confirm the part in under a minute.
- Engine code stamped on the block, never just the capacity
- Oversize required, if the bores have been machined
- Whether rings and gudgeon pins are included
- Compression height and pin diameter for the specific application
Pistons questions
What information is needed to order pistons?
The engine code from the block and the oversize required. Capacity alone is not enough, because manufacturers run several engine families at the same capacity with entirely different internals.
Do pistons come with rings?
It varies by line and application. Confirm with the branch whether rings and gudgeon pins are included so nothing is missing when the engine is on the bench.