What does cylinder head contact mean?
2 Answers
Engine cylinder head contact occurs when the connecting rod is too long due to excessive clearance, causing it to hit the engine cylinder during operation, which is referred to as cylinder head contact. If an engine experiences cylinder head contact, it usually means the engine is scrapped. Additional details are as follows: Causes of cylinder head contact: When there is an issue with the connection between the piston and connecting rod, such as excessive clearance, the piston may exceed its normal operating trajectory, directly hitting the cylinder head. A dropped timing chain or belt, or a broken crankshaft pin, can also cause cylinder head contact, known as timing jump. This happens when the timing belt has been in use for too long or exceeds its service life, the tension adjustment device fails, or the timing belt and timing gear do not fit tightly, creating a gap. Valve issues can also lead to cylinder head contact, such as a stuck valve stem, broken intake or exhaust spring, or a valve falling into the cylinder. During repairs, using incorrect piston sizes, overly thick connecting rod bearings or shims, or a damaged cylinder block surface can also cause the piston top to be too high.
When repairing car engines, I've heard the term 'piston-to-head contact' countless times. It refers to the piston suddenly hitting the cylinder head while moving in the cylinder, like two hard objects colliding, instantly destroying the engine. Common causes include loose piston pins or bent connecting rods, which are particularly prone to occur in modified cars. Some car enthusiasts increase piston size to enhance performance, but improper installation leads to piston-to-head contact. I once encountered an owner whose engine suffered piston-to-head contact after aggressive driving on the highway, requiring a complete engine overhaul with replacement parts costing over ten thousand yuan. Therefore, I recommend regularly checking piston clearance during maintenance, using appropriate lubricants, and avoiding excessive modifications or overloading the engine to prevent such accidents. Always seek professional technicians for repairs—don't cut corners to save time or money.
