Diagnosing a Cracked Head or Blown Gasket on a Bobcat 773G

[MikePhua]

The Bobcat 773G is a well-known and reliable skid-steer loader in the construction and agriculture industries. As with any piece of machinery, components like the engine and its associated systems may encounter issues over time, and one of the more serious problems an operator might face is a cracked cylinder head or a blown head gasket. These issues can cause significant performance problems and, if left unresolved, can lead to more severe damage to the engine. This article explores the potential causes, symptoms, diagnosis, and solutions for dealing with a cracked head or blown gasket in a Bobcat 773G.
Understanding the Bobcat 773G and its Engine
The Bobcat 773G skid-steer loader is powered by a reliable engine that provides the necessary force for lifting and maneuvering materials in tough conditions. The engine features a high-flow hydraulic system, offering impressive power for various attachments. The 773G is equipped with a compact design, making it a popular choice for tight spaces, offering excellent maneuverability.
The engine is crucial for the loader's overall performance, and issues with the cylinder head or head gasket can significantly affect how the engine runs. Understanding the engine's key components can help in diagnosing problems when the machine starts to show signs of malfunction.
Cylinder Head and Head Gasket: Key Components

• Cylinder Head: The cylinder head is an essential component that sits atop the engine block. It houses critical parts like the valves, camshaft, and spark plugs. The head is responsible for managing the intake and exhaust of gases from the cylinders. A cracked head can lead to a loss of compression, oil leaks, coolant leaks, and, in severe cases, total engine failure.
  
• Head Gasket: The head gasket seals the cylinder head to the engine block. This gasket prevents coolant, oil, and air from mixing and ensures the engine operates efficiently. When the gasket blows, it can result in coolant mixing with engine oil or exhaust gases leaking into the coolant, which can cause overheating, engine damage, and poor performance.
  

Signs of a Cracked Cylinder Head or Blown Gasket
Several indicators suggest that the Bobcat 773G’s engine may be suffering from a cracked cylinder head or blown head gasket. These symptoms may appear individually or together and typically include:

1. Overheating: The most common sign of a cracked head or blown gasket is engine overheating. If the coolant is leaking due to a damaged gasket, the engine will not be able to regulate its temperature effectively, leading to overheating and potential engine damage.
   
2. White Smoke from the Exhaust: If coolant is leaking into the cylinders due to a blown gasket, it will burn off during the combustion process, producing white smoke from the exhaust. This is one of the classic signs of a blown head gasket.
   
3. Loss of Power: A cracked cylinder head or blown gasket can cause a loss of engine compression, which can significantly affect the engine’s power output. If the engine is not producing enough power to perform normal tasks, this could be a direct result of a cylinder head or gasket failure.
   
4. Coolant in Oil: One of the clearest signs of a blown gasket is the presence of coolant in the oil. If you notice that the oil on the dipstick has a milky or frothy appearance, this indicates that coolant has entered the engine oil, which can lead to severe engine damage if not addressed immediately.
   
5. Oil in the Coolant: Similarly, if oil enters the cooling system due to a blown gasket, you may see oil in the coolant reservoir. This can create blockages in the cooling system, leading to further overheating.
   
6. Visible Leaks: If the cylinder head is cracked, you may notice visible fluid leaks around the head or the gasket area. This can include coolant leaks or oil leaks, which may be more noticeable when the engine is running.
   

Diagnosing the Issue
If you suspect that the Bobcat 773G has a cracked head or blown gasket, a thorough diagnostic process is required to confirm the problem. Here are the steps typically involved:

1. Check for Symptoms: First, observe the symptoms listed above. White smoke, coolant in the oil, and overheating are all strong indicators that something is wrong with the head or gasket.
   
2. Pressure Test: Perform a cooling system pressure test to check for leaks. If the system cannot hold pressure, it’s a clear sign that there’s a breach somewhere, likely caused by a cracked head or blown gasket.
   
3. Compression Test: A compression test on the cylinders can help determine if there’s a loss of compression due to a cracked head. If one or more cylinders are not producing sufficient compression, the head or gasket may be to blame.
   
4. Cylinder Leak-Down Test: A cylinder leak-down test helps isolate the issue more precisely by testing how much air escapes from the cylinders when they are pressurized. If there’s significant leakage, it can confirm a problem with the cylinder head or gasket.
   
5. Visual Inspection: Carefully inspect the cylinder head and gasket for signs of damage, cracking, or warping. Any visible cracks or irregularities on the surface of the head indicate a serious issue that may require a replacement.
   

Repairing the Cracked Cylinder Head or Blown Gasket
Once you have diagnosed the issue, the next step is to determine the best course of action for repairs. Depending on the severity of the damage, there are a few options:

1. Replacing the Head Gasket: If the gasket has simply failed without damaging the cylinder head, replacing the head gasket may be sufficient. This involves removing the cylinder head, cleaning the mating surfaces, and installing a new gasket before reassembling the engine.
   
2. Repairing or Replacing the Cylinder Head: If the cylinder head is cracked or severely damaged, it may need to be replaced entirely. In some cases, the head may be repairable by welding or using a specialized sealant, but this depends on the extent of the damage.
   
3. Resurfacing the Cylinder Head: If the head is warped but not cracked, it can sometimes be resurfaced to restore proper contact with the gasket. However, this is only possible if the warping is within acceptable tolerances.
   
4. Additional Checks: While replacing the head gasket or cylinder head, it’s important to check for any other underlying issues, such as damaged pistons, valves, or the cooling system. Make sure the entire system is properly sealed and functioning before reassembly.
   

Preventative Measures
To reduce the likelihood of head gasket or cylinder head failure, operators should take proactive steps:

1. Regular Maintenance: Ensure that the engine is regularly serviced, including checking coolant levels, oil quality, and overall engine performance.
   
2. Monitor Overheating: Always keep an eye on the temperature gauge during operation. If the machine starts to overheat, address the issue immediately to prevent further damage.
   
3. Use Quality Coolant: Use the recommended coolant and ensure that the radiator and cooling system are regularly flushed and cleaned to prevent blockages.
   
4. Avoid Excessive Strain: Avoid overloading the Bobcat 773G, as excessive strain can lead to overheating and increased risk of gasket or head failure.
   

Conclusion
A cracked cylinder head or blown head gasket on a Bobcat 773G can cause significant issues, but with the right diagnostic steps and repair procedures, it is possible to resolve the problem and get the machine back to work. By paying attention to symptoms like overheating, power loss, and fluid contamination, operators can identify problems early and take preventive measures to extend the life of their equipment. Regular maintenance, including coolant checks and timely repairs, will help ensure that the 773G continues to perform at its best for years to come.