How to repair an engine cylinder head

A car engine should be adequately cared for the same way as the car because, without it, the vehicle would not function at all.

Inside the engine are found individual parts all working together in a way that when the gas pedal is pressed, the car will automatically get going.

Cylinder heads are the most vulnerable parts of a car's engine and as a result, must be adequately cared for upon a total breakdown. They are placed on top of the engine block to cover its cylinders and then create the combustion chamber. Mostly for traditional gas-powered cars, they rely on cylinder heads to help power their vehicles. Inside the internal combustion engine exists cylinders and also within these cylinders, gas and air mix sparking into combustion.

It is these combustion forces that drive the chain of the vehicle to move and also transfers energy to the driving wheels of the car. Cylinder's heads are often made of sturdy materials. On older cars, they are usually made of iron, and modern cars might go for aluminum regarding the choice of material. But even as they are made of durable metals, they are also light-weight. If the cylinder gets too heavy, it might not be able to complete its movements, and that would lead to the inefficiency of the engine.

Because of constant changing temperatures and high-pressure levels, the head should be robust enough to withstand the high level of demand required of it without a break or even a crack. The heads are close to the cylinder and then open to vent the exhaust gases. They function this way, many times per minute, and every time they close, they create a pressure seal within the cylinder, and whenever they open, they are often enveloped in hot gases. An aluminum cylinder would be most likely last for five years while the iron one can last a little longer, from six to seven years.

CAUSES OF CYLINDER HEAD FAILURES

The most common cause is overheating caused by either coolant loss, head gasket failure, or restricted flow of coolant. In extreme cases, a cracked or damaged cylinder head can cause great damage to the whole engine, and to prevent this from happening, you must treat the issue as a matter of urgency. Cylinder heads can, because of too much pressure mounted on them, warp. What this means is that it will no longer provide a flat surface to hold the head gasket in the right position, and this can cause significant problems much later on in the form of major repairs or total engine replacement needed.

Warping is a common problem for aluminum-made cylinder heads. It all depends on the type of engine as different engines have their level of tolerance: while some can withstand a high level of warping, others cannot.

SYMPTOMS OF CYLINDER HEAD FAILURES

It is imperative to regularly inspect one's internal combustion engine to notice a possible crack on time. Well, some symptoms will present themselves whenever such happens to draw one’s attention to them. The signs of cylinder head failures vary, and it is essential that drivers can take notice of them with immediate effect to limit excessive damages. Whatever happens to the cylinder head will lead to the breakdown of the engine

Below are symptoms to look out for when cylinder heads fail:

Leakage of coolant upon the damage of a cylinder head:

This is possibly by a crack. Coolant usually leaks out of it together with oil. This causes too much heating of the engine and a warning sign from the vehicle on your dashboard. Make sure always to check the amount Of coolant left.

The weak performance of the engine:

One of the first symptoms is mostly engine weakness. When there is a crack on the head, compress air would escape from the combustion chamber, and you will notice the engine running slow or abnormal if such happens.

Exhaust smoke:

Big cracks in the cylinder head allows exhaust gases to leak out and cause smoke emanating from the engine. This is a rare occurrence, and once happens shows that you'd be needing a new cylinder head right away.

Misfiring engine:

When the cracked cylinder heads severe, the mixture in the combustion chamber won’t be enough to fire up the engine. Your engine might go dead repeatedly while driving, and you'd have to keep turning it back until you arrive at your destination.

Oil droplets:

Cylinder heads typically have oil in it, and when you have a cracked head, oil might begin to leak out of it. The oil indicator will display on your dashboard as it turns on.  Once you see this light on, try to open your hood and check if there is oil near the cylinder.

HOW TO REPAIR CYLINDER HEADS

The cylinder is the core of the car's engine. It is there you’d find a piston moving up and down, compressing the gas, and driving your vehicle to move. The cylinder head sits at the top sealed by a head gasket. Cylinder head repairs are an engine fix done in most shops. The aluminum cylinder heads are indeed a bit reliable, but they are not without weaknesses. When you notice any of the symptoms or indicating a cylinder breakdown, then it becomes urgent that you come in for a fix. If you wait a lot longer, it may become a blown head gasket and might cost ten times more.

It all depends on the size or location of the cracks, the value of the casting, and what it will take or cost to replace the casting. When a crack is bad and looks beyond repair is probably not worth the time and efforts after all. But if the crack happens in an old model cylinder head, which is pricey and hard to find, it would be proper to fix it using appropriate techniques.

This comes down to weighing the cost of repair over the cost of replacement. The head blocks should always be checked out carefully for cracks any time is used, and the mileage engine is being rebuilt. A magnetic particle inspection technique will reveal surface down to the depth of about a quarter of an inch on cast-iron block and heads. Although some areas might be hard to inspect using this method, this is where pressure testing is required to check unseen and hidden cracks in the exhaust ports and water jackets.

When it comes to aluminum casting, cracks and porosity leaks usually are found by penetrating dyes or pressure testing, which will uncover any porosity leaks or cracks. Pressure testing at 10 to 40 PS1 often reveal any porosity leaks or cracks worth worrying over. It is another technique that can uncover cracks that might be overlooked at room temperature.

When a crack is being identified, it is very paramount to scrutinize the casting to determine the extent of the cracks. Visible cracks on the surface of a casting often extend some distance under the surface in both directions. The repair technique for fixing a crack depends on the type of metal used, (either iron or aluminum),  the location of the cracks, and its size.

Cracks appear at the areas between the valve seats and spark plug hole, the deck areas between combustion Chambers, the top center area of the head, and the exhaust parts. It can also start in the combustion chamber, extending into exhaust parts. To blind holes, open bolt holes or valve guides.

In the block, it can occur between the cylinders on the deck surface, the cylinder walls, or in the web area around the main bores and crankshaft. Around the lifter bores or Cam bores or even in the sides or condors of the block near motor mounts or expansion plug openings.

Crack repairs are cost-effective alternatives to buying a new or used casting to replace a cracked head or block. Below are different options to repair cracks:

Pinning Cracks

Pinning is the most used technique for repairing cracks in cast iron heads and blocks because its fast, economical, and reliable. Cracks in aluminum heads and blocks can be repaired using this same method even though TiG welding is more preferred for aluminum.

The only thing required of in tools is a drill, guide fixture, and tap. Pinning is all about drilling holes in a crack, installing warlepping pins to fill the crack, the penning over the pins to seal and blend the surface. The two major types of pins are: straight and tapered. 

Tapered pins pull themselves into a Crack as they are tightened to provide a tight seal along the entire length of the pin. This happens because the thread on both the tapered pin and holes have an interference fit. The holes must be hand-tapered carefully, and the pins tightened for a strong seal.

Straight pins are much faster to be installed. They are designed to twist off when they are tight and eliminate the need to cut the heads off. Straight pins can also reduce the need for installing valve seat inserts in iron cast heads. It is not all types of cracks that can be handled by ordinary tapered and straight pins.

Such cracks like an area of casting that can open upon being pulled apart when the casting is under load or gets hot. These types can be dealt with locking devices, or pins with a self-gripping ability. Also, cracks that happen in fragile areas of casting wouldn't be held by bolts unless there's sufficient metal to grip and support the threads.

Furnace Welding Cast Iron

This method requires skills and expertise. Cracks in cast iron can be repaired using this technique, but it requires pre-heating the casting before proceeding to weld it and also lots of heat. The casting must be slowly cooled even to eight hours after welding so it wouldn't recrack.

The crack needs to be prepared carefully on time, for you cannot just hit up a head with a weed burner. The head should be pre-heated in an enclosed furnace or oven so that it would come up to the head through the bottom. The head needs to be insulated with a blanket and drafts prevented while welding or a crack might occur or porosity in the weld.

The head will then be cooled slowly later on. When the temperature of the heated head has stabilized, a neutral flame “oxyacetylene torch" with slightly more acetylene than oxygen is used to melt the cast iron. Filler rod and borax flux will be used to fill the crack.

This is used to clean the weld by adding a little flux so that the dirt will rise upwards and float out of the repair areas with the torch filling the hole with a graphite plug when a valve seat is furnace welded. Then proceed to weld around it. The puddle will be about half an inch deep and maybe two inches in diameter. Once the crack has been filled, then it will slowly cool down.

To be successfully done, the casting must follow this process to cool off. Wrap the head in an insulating blanket and keep it in a hot box so that it will cool. After the head cools, it will be cleaned to remove the scale, rough machined, and submersion pressure tested in hot water at 100 PSI to check for leakages.

Spray Welding Cast Iron

This technique can make a strong repair just like hot welding but with a much lesser heat. There is still a need to pre-heat and post-heat to avoid recracking. Flame spray welding is done with a special oxyacetylene torch with a trigger operated hopper that injects nickel alloy powder into the flame. It has a hardness of 18 to 22 RC. Cracks in the valve seat area may re-open or pressed in by a new valve seat.

Braze Welding

This is great on damaged bolts holes and crack head part. The casting heats up to about 400-500 degrees and does not melt. For repairing cracks in the tops of thin-wall cylinder heads and small cracks in exhaust ports, this is a perfect choice of repair.

COST OF CYLINDER HEAD REPAIR

This depends on the valve of the cylinder's head and the price incase it stops to work effectively as it should. The cost to repair a head in Australia starts at $500 depending on the complexity of the head or engine. These doesn’t include refitting to the engine. It usually is cheaper, in the long run, to replace with quality aftermarket parts.