Piston seizure is a common engine problem. In automobiles and trucks, however, the problem is seldom noticed. A piston may seize but the other pistons push it through the engine cycle, and it is freed up rather quickly. The most common symptom is a bent or broken piston rod. In smaller engine applications such as lawnmowers, scooters, and motorcycles, however, the pistons often seize in the cylinder and have to be removed so repairs can be made. The most common cause of a seizure is lack of lubrication.
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Things you need
- Penetrating oil
- Soft-faced hammer
- Propane torch
- Cylinder hone
Soak the cylinder above and below the piston with penetrating oil. Let the cylinder soak for about eight hours. Attempt to move the piston by turning the crankshaft nut of the vehicle both clockwise and counterclockwise. Repeat this procedure a few times, allowing the oil to soak the piston and the cylinder.
Soak the cylinder again with oil, and tap the face of the piston on both the exhaust and intake sides with the soft-faced hammer. Attempt to turn the piston again. This should knock any debris loose from between the piston and the cylinder walls. This is sometimes necessary if the cylinder has been infused with water, such as when a watercraft or boat engine is submerged.
Remove the rod and cylinder from the engine and gently clamp the cylinder in a vice. Heat the sides of the cylinder briefly with the propane torch; this will cause it to temporarily expand. While the cylinder is still warm, tap the top of the piston with the soft-faced hammer. This should allow the piston to slide through the cylinder.
Hone the cylinder above the piston and try Steps 2 and 3 again with the cylinder in the vice. If the piston still does not become free, it is time to purchase a new cylinder, piston and rod. At this point, even if the piston could be removed, the cylinder and piston are probably damaged beyond repair.
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