Automotive Maintenance: Cause Analysis and Detection Method for a Burnt Engine Head Gasket

1 Causes of cylinder gasket burnout

1.1 Uneven tightening of nuts (bolts) of cylinder head leads to burnt cylinder gaskets

(1) During operation, nuts (bolts) of cylinder head are not regularly checked and tightened, and individual nuts (bolts) of cylinder head are loosened, so that cylinder head cannot be evenly pressed against cylinder block.

(2) When tightening nuts (bolts) of cylinder head, first tighten two rows of nuts in middle, and then tighten them alternately from middle to left and right, otherwise nuts (bolts) will not be tightened evenly, causing cylinder gasket to be uneven Clamped between cylinder block and cylinder head.

(3) Use a torque wrench when tightening nuts (bolts) of cylinder head. For convenience, some maintenance workers use a regular wrench to fasten, which results in inconsistent torque, some bolts are over-torqued, and some bolts are over-torqued, resulting in cylinder head not being evenly pressed against cylinder block.

(4) The tightening torque of nuts (bolts) of cylinder head is greater than specified value and too large, resulting in cracks in cylinder head. The cylinder head bolts and threaded holes have slipped and deformed, or bolts have elongated and body threaded holes have risen so that seal between cylinder head and body is not tight.

The above conditions lead to insufficient pressure on mating surface of cylinder block and cylinder head, poor sealing of mating surface, release of high-temperature and high-pressure gas from gap with low local torque, and cylinder head gasket burns out.

1.2 The surface of cylinder head-to-body connection is uneven, causing cylinder gasket to burn out

(1) Careless inspection when repairing and replacing parts, which caused warping and deformation of joint plane of cylinder head or body, or presence of carryover, rust, pits and pits, etc., which cannot be repaired and polished at time causing cylinder The flatness of lower surface of cover or upper surface of body exceeds set value.

(2) When replacing prechamber or swirl chamber insert, insert is out of specification. When insert is too thick and protrudes from plane of cylinder head, cylinder head, cylinder gasket, and cylinder liner cannot be pressed evenly when insert is too thin and is below plane cylinder head, gas will come out of insert.

(3) Incorrect height of cylinder liner shoulder protruding from body plane. If protrusion is too large, cylinder liner shoulder will hold cylinder head so that cylinder gasket cannot be flat.tightly pressed; if protrusion of body plane is too small or has no protrusion, or even lower than body plane, cylinder head cannot be pressed against cylinder. Sleeve, cylinder gasket cannot be compressed, and it cannot be well sealed.

(4) The height difference of top surface of cylinder liner shoulder of each cylinder of a multi-cylinder diesel engine protruding from plane of cylinder body is not constant.

The above conditions will cause cylinder head gasket to lose its function, degrade sealing of cylinder, and high temperature gas will escape from gap, causing cylinder head gasket to ignite.

1.3 Incorrect use and assembly will burn cylinder gasket

(1) The cylinder head gasket has been used for too long, and cylinder head gasket has lost its elasticity after repeated disassembly and reassembly.

(2) During installation, carelessly remove carbon, dirt, rust, and raised crusts from mating planes of cylinder head, cylinder gasket, and body, which will leave gaps between mating planes after installation.

(3) During installation, cylinder gasket has a one-sided flare or folded edge. By mistake, side with flare or folded edge faces plane of cylinder body, so that gas can easily rush into inside of cylinder gasket from flare.

(4) When installing, lubricate cylinder gasket surface with oil, or soak cylinder gasket directly in diesel fuel, take it out and install it again, etc.

The above conditions and causes burn through cylinder head gasket easily.

1.4 Diesel engine temperature too high to cause cylinder gasket fire

(1) The compression ratio is too high or compression gap is too small, so that pressure at end of compression is too large and temperature generated during expansion and combustion is too high.

(2) The fuel advance angle is too small or too large, causing diesel engine temperature to become too high and heat not transferred in time, causing cylinder head and cylinder block to overheat. .

(3) Incorrect valve timing; intake or exhaust system is blocked, resulting in insufficient intake air and exhaust pollution; poor lubrication of relevant moving parts; cooling system malfunction, poor heat dissipation, etc. overheating.

(4) The locomotive is often overloaded or diesel engine is overloaded for a long time, and diesel engine generates high temperature due to excessive load.

In above situation, cylinder head gasket suffers from high temperatures for a long time, asbestos material deteriorates, hardens, gradually loses its elasticity and burns out.

1.5 Cylinder gaskets ploho made and cause burnout

(1) The quality of material used to make cylinder gasket is too low, not enough elasticity, not resistant to high temperatures, and cannot meet sealing requirements of cylinder head-cylinder body joint surface.

(2) Due to poor processing technology, manufactured cylinder head gasket is sloppy, flanging is loose, thickness of asbestos paper inside metal shell is uneven.

(3) The positional distance and geometric shape of produced cylinder gasket holes do not meet specifications, such as incorrect position of cylinder gasket bolt holes, incorrect position of cylinder liner hole of cylinder gasket, and incorrect position of cylinder gasket water channel hole.

In above situation, even if cylinder head gasket can be difficult to install, there will be unevenness, insufficient pressure, and incomplete pressure, resulting in cylinder head not sealing well against cylinder body and high gas temperature. impact will burn through cylinder head gasket.

2 Cylinder Gasket Burn Detection Method

Use cylinder pressure gauge to check compression pressure in two adjacent engine cylinders. If they're both low, it's usually cylinder gasket that isn't sealing well. Then perform following specific tests.

(1) Use a rubber hose to check cylinder head gasket for leaks. Start engine, bring one end of rubber hose to your ear, and look for other end along connection of cylinder head to cylinder block, which may be poorly sealed. sound is clearly audible at leak.

(2) Check tightness of cylinder gasket by looking at spray of water from radiator. Open radiator cap, let engine idle, keep an eye on coolant fill hole in radiator, and quickly depress accelerator pedal fully. The more air bubbles, more serious air leak. In severe cases, radiator neck flips over and splashes at idle.

(3) Use a gas analyzer to check tightness of cylinder head gasket. Some of engine radiator coolant fill holes are under iron plate, making it impossible to see air bubbles. The radiator cap can be opened, and gas analyzer probe must be placed on open radiator cap. Do not touch coolant.

(4) Cylinder gasket leakage will cause engine temperature to be too high and power to drop. It should be timelyReplace it carefully, otherwise cylinder head will be easily damaged, cylinder head will be scrapped, and coolant will flow into combustion chamber.

3 Cylinder Head Gasket Burnout Prevention

(1) The disassembly of cylinder head should be carried out when engine is cold, and it is strictly forbidden to disassemble hot engine to prevent warping and deformation of cylinder head. When disassembling, it should be gradually loosened symmetrically from both sides to middle. If cylinder head is firmly connected to cylinder block and is difficult to remove, it is strictly forbidden to hit cylinder head with a metal object or insert a sharp tool into seam to pry it strongly so as not to scratch connection surface. between cylinder block and cylinder head or damage cylinder gasket.

(3) When installing cylinder gasket, first check whether plane of cylinder head and body is straight or curved. Inspection Method: Use a ruler longer than cylinder head, place them on plane of body and cylinder head respectively, measure with a thickness gauge to make sure it conforms to regulations. Otherwise, it should be polished and smoothed.

(4) The selected cylinder head gasket must have same characteristics as original cylinder, and surface must be smooth, not damaged, wrinkled or hardened by aging, and not too thick or too thin. For some high-strength, high-power imported supercharged diesel engines, bare metal cylinder head gasket used must face cylinder head marked (such as TOP or UP) during installation (normal cylinder head gasket should not be used instead). and cylinder neck. The elastic ribs on oil port and water port must be intact.