ABOUT USED PISTONS
WHAT IS THE PISTON?
A piston is the disk or short cylinder filling that is located entirely inside a tube. The piston moves up and down against a liquid - usually fuel - inside of an internal combustion engine.
WHAT DOES THE PART DO?
The piston works by transferring the force output of an expanding gas from the cylinder to the crankshaft. This action provides rotational action for the flywheel.
WHAT DOES THE PART LOOK LIKE?
A piston is a cylinder that measures up to 35 millimeters in diameter and about four to seven inches in height. The part is made out of low carbon steels or aluminum alloys.
WHERE IS THERE PART TYPICALLY LOCATED ON THE VEHICLE?
The piston is located in the cylinder block. It is housed inside a cylinder.
WHAT DO YOU LOOK FOR IN A USED PISTON?
You will want to look at the piston’s crown as well as the cylinder walls. Because this is a moving part that undergoes lots of stress, you want to make sure that the piston is free of any cracking. Also, you want to make sure that the piston’s pin bore is not worn more than .002 inches in diameter.
WHAT ELSE SHOULD I KNOW ABOUT A PISTON BEFORE I PURCHASE ONE?
Before you purchase the piston, you will want to buy the rings first. That’s because you want to make sure that a compatible ring is available for the piston that you will put into the car.
Also, if you are buying pistons for a diesel engine, then be aware that diesel pistons are not the same as those used on gasoline engines.
WHAT OTHER PARTS ARE CONNECTED OR THAT I MAY NEED FOR THIS PART?
Pistons are connected to the crankshaft via connecting rods. If you are going to install a piston in a car, then you will need the following tools and materials:
- Protective gear such as goggles and gloves.
- A ring compressor that is used to place the piston into the cylinder.
- A piston ring expander tool.
- Assembly oil which is used to lubricate the piston parts.
- Towels to clean the cylinder.
WHAT SIGNS OF WEAR SHOULD I LOOK AT WHEN BUYING A USED PISTON?
Here are the signs of wear that you should look for when buying a used piston:
- Make sure that the rings on the piston are not completely worn out.
- Check for any piston crown damage. The crown is located at the top of the piston. Damaged crowns can have excessive scratches or cracks.
- Also check for piston skirt damage. A damaged piston skirt will appear misshapen or deformed.
WHAT IS THE AVERAGE LIFESPAN OF A PISTON?
The average lifespan of a piston is anywhere between 16,000 and 24,000 hours of use.
WHEN SHOULD THE PART BE REPLACED?
A piston should be replaced when the pin bore is more than .002 in diameter. Also, a piston should be replaced if the vehicle is exhibiting any of the following behavior:
- Excessive grey smoke coming from the engine
- The vehicle is using more oil than usual
- The vehicle is experiencing decreased performance
FREQUENTLY ASKED QUESTIONS ABOUT PISTONS
HOW TIGHT SHOULD A PISTON BE IN THE BORE?
The tightness should be at .003 inches. However, a measurement up to .006 inches is acceptable.
WHAT DOES A BAD PISTON SOUND LIKE?
A bad piston will have a hollow, bell-like sound. This is caused by the piston rocking back and forth inside the cylinder.
SHOULD PISTON RINGS BE LOOSE?
Piston rings should move slightly when jiggled.
HOW MUCH SPACE SHOULD THERE BE BETWEEN THE PISTON AND THE CYLINDER WALL?
The gap should be 0.03 mm for every 10 mm of cylinder diameter.
CAN AN ENGINE RUN ON A BROKEN PISTON?
Yes. a piston can run on a broken piston. However, that piston should be replaced as soon as possible.