What is a cylinder head?
There different types of engines, namely over-head-valve (OHV) and over-head-camshaft (OHC), we'll use the OHC engine for reference. The engine block, or cylinder block, contains the crankshaft, connecting rods and pistons, the pistons are housed in, and travel, in what are known as cylinders. The cylinder head fits on top of the block and covers the cylinders, but note, that between the head and block, a cylinder head gasket is used to ensure the combustion process is sealed and coolant and oil do not leak as they travel through the engine for cooling and lubricating.
Check out this video for a better understanding of how an engine works and the role the cylinder head plays.
What causes cylinder head failure/damage?
Cylinder heads can fail in a manner of ways:
- Internal parts of the cylinder head suffer mechanical failure
- Warped beyond economical repair or warp repaired too many times before, i.e over-skimmed
- Pre-combustion chambers (diesel engines) sink in or protrude and the head cannot be repaired due to the material of the chambers (ceramic chambers cannot be skimmed and the head must be replaced) or replacement chambers are unattainable
- Corrosion of the cylinder head due to over-fueling or coolant impotence
What causes cracking?
- Commonly the engine overheats to the point of cracking
- Overheats and cold water is immediately poured into the radiator causing a difference in temperature, like putting a cold cup into the microwave
- Metal fatigue due to sustained variation of stress
What causes mechanical failure?
Can be caused by various factors and can result in such catastrophic damage that may require the some, if not most, of the mechanical parts to be replaced, or worse the engine to be replaced due to pistons hitting the valves, bending them, breaking camshafts/rockershafts, lifters or rockers, destroying pistons. Factors include:
- Timing component failure resulting in piston valve contact (interference engine)
- Dropped valves resulting in damage to the cylinder head from the valve embedding back into the cylinder head and damage to the pistons,
- Dropped valve seats resulting in debris lodging into the face of the cylinder head or worse
- Mechanical components coming loose, for example nuts or bolts loosening, shims dislodged
- Failure or incapacity of auxiliary engine parts, like insufficient oil lubrication resulting in seizure
- Poor maintenance for example oil turning into sludge
What causes warping or sinking of combustion chambers?
Warping of the cylinder head, particularly referring the face of the head (the part that makes contact with the head gasket and block), is caused by overheating. The cylinder head may not crack but the face is gets warped when it should be flat. The cylinder head can be repaired by skimming, however, if it has been skimmed before then there may not be sufficient material to skim, therefore a new cylinder head is needed.
Sinking of the pre-combustion chambers, occurs when the engine overheats and if the chambers and the cylinder head are made of two different materials, for example, an oem Colt 2.8 4M40 cylinder head is made of aluminium whereas the pre-combustion chambers are ceramic, as they expand and contract at different temperatures, the combustion chambers may be smaller than the hole it was made for and sink in. Since ceramic chambers cannot be skimmed, it is more viable to replace the cylinder head.
What causes corrosion?
- Over-fueling, burning too rich, or old coolant can result in corrosion or pitting of the metal
- Over-fueling is when there is too much fuel being consumed by the engine caused by a malfunctioning fuel regulator or leaking injectors (the part that injects the fuel into the engine during operation) resulting in the cylinder head being corroded.
- Coolant has anti-corrosion properties and if not changed on time or being of poor quality can result in corrosion
Can a cylinder head be repaired?
Depending on the severity of the damage, a cylinder head can be repaired, however, you have to consider whether it is economical to repair.