With all the various automotive components available today, it isn’t always easy to know what cylinder heads to use for a vehicle.
When looking at the different choices out there, the 862 heads are a popular choice because of the robust nature of the casting.
It can withstand high temperatures, deal with above-average pressure, and is made with various metals.
The goal of the 862 design is to provide more airflow into the cylinder to deploy the fuel more efficiently, ensuring that the combustion process remains consistent.
Could this third-generation design be a suitable choice for your vehicle?
Are 862 Heads Any Good?
The aluminum 862 heads are a lightweight choice for engine design. This attribute contributes to improved fuel economy ratings while dissipating heat more efficiently. They’re typically found in high-performance designs, such as race cars, while providing the other features of this casting.
General Motors is responsible for manufacturing the 862 cylinder heads. They’re a sand-cast product designed to provide more compression than similar products. That gives this option an advantage, especially when compared to 799s.
Since the 862s come with a compression ratio that leads to an increase of in-cylinder pressure, you receive a faster ignition and higher rate of heat discharge with the updated design.
That helps the combustion process run with extra smoothness and efficiency.
Here’s a closer look at the 862 heads with their features and specifications.
| 826 Heads Features | 826 Heads Specs |
| Materials | Most 826 heads are made with aluminum. Some designs are using stainless steel. |
| Part Number | 12559863 |
| Intake/Exhaust Port Shape | Intake – Cathedral; Exhaust – D-Port |
| Intake/Exhaust Port Volume | Intake – 200 cc; Exhaust – 70 cc |
| Combustion Chamber Volume | 61.15 cc |
| Intake/Exhaust Valve Meter | Intake – 1.89 inches; Exhaust – 1.55 inches |
| Compression Ratio | 9.5:1 |
GM designed the 862 heads to be compatible with LR4, LM4, and LM7 engines. It sits on top of the engine block to cover the cylinders, creating a combustion chamber that generates energy.
You get the space needed to feed fuel and air to the cylinders while staying sealed in place with the use of a head gasket.
Why Are 862s a Popular Choice Today?
The reason why 862s are a great choice for a compatible vehicle is due to the improved compression it delivers after porting.
Although you might not experience the same flow benefits when compared to 243s, they still deliver the power and performance needs for some vehicle designs.
The 862 design isn’t meant to be sophisticated. It’s a straightforward option for high-performance vehicles that works well, especially if you’re not satisfied or the placement is incompatible with 706 heads.
Are There Any Issues with the 862 Heads?
The most common problem noted with 862 heads is an issue that affects almost every other design as it ages. There is a risk of cracking due to heat, moisture, or overuse that eventually allows coolant to flow into the oil.
If that issue isn’t fixed, severe engine damage can occur that may require a higher cost to fix than the vehicle is worth.
The only way to repair a cracked cylinder head is to replace it with another. You can buy the part directly to save some money, and then reduce expenses even more if you can do the work yourself.
Signs and Symptoms of Cracked 862 Heads
The symptoms you can experience when 862 heads crack are quite variable. It’s essential to recognize them as quickly as possible to avoid engine damage and having the vehicle break down.
There are four primary symptoms that you’ll notice when the cylinder heads crack during vehicle operation.
- You experience an immediate drop in oil levels.
- The coolant levels get lower without evidence of a leak or its temperature changes.
- The engine performance starts suffering.
- You begin to see smoke coming out of the vehicle’s exhaust.
The most common reason for a cracked cylinder head involves the vehicle overheating. When this issue occurs, you might have the coolant flow restricted or experience head gasket failure.
In extreme instances, a damaged or cracked cylinder head can result in the engine failing to operate permanently.
Most garages and mechanics can recondition and repair a cylinder head for a reasonable price. It depends on the value of the part and how much labor is needed to complete the work.
How to Work on a Cracked Cylinder Head to Recondition It
If you’re interested in repairing an 862 (or whatever is equipped to your vehicle), these steps can help you have a successful experience.
You’ll need a few materials before getting started. That includes a valve spring compressor, needle-nose pliers, and a high-quality ratchet and socket set.
The job also requires a wire brush, solvent, and a gasket scraper.
Before you start working, please remember to disconnect the negative terminal from the vehicle’s battery to avoid a potential shock.
Once you have the necessary items, you’ll want to follow these steps to manage the repair process.
1. Drain the Coolant and Oil
Since a cracked cylinder head can cause coolant to go into the oil, you’ll need to drain both fluids before starting.
This step prevents a mess while helping you flush away the potentially contaminated materials.
You’ll need to open the radiator drain cap first. After all the fluid is finished draining, take out the oil pan plug.
2. Remove the Cylinder Head Parts
Using the tools you’ve collected for repairing your vehicle, you’ll now disassemble the various components in the following sequence.
- Intake and Exhaust Manifolds
- Timing Belt or Chain
- Rocker Arm
- Valves and Valve Keepers
- Valve Springs, Seals, and Rocker
Some vehicles come with multiple rocker arms. After removing the components, it helps to place each part in a labeled container to make the reassembly work easier.
3. Remove the Cylinder Head
Each manufacturer has a recommended sequence for taking the cylinder head off correctly. You’ll want to follow those instructions exactly to avoid unintentional damage to the vehicle or engine.
Loosen and remove the mounting bolts for the cylinder head. Once you have them gone, it’s time to take off the head from the engine block.
4. Clean the Cylinder Head
The cylinder head will be covered in a greasy, sludge-like material. You’ll need to remove any carbon deposits on the interior or exterior of the part before proceeding.
You’ll need to clean the coolant and oil passageways as part of this step.
5. Examine the Cylinder Head
Once the cylinder head is clean, it can be inspected for damage. You’re looking for pits and cracks in the part. If you see openings, an epoxy sealant can help you restore life to the unit.
Although they’re marketed differently, there isn’t a difference between the epoxy used for aluminum heads like the 862 or iron ones.
You might consider measuring the camshaft with a micrometer to see if the dimensions fall within the manufacturer’s specifications.
If you’re unsure of what these specs are, they should be published in your owner’s manual.
This step is also an excellent time to inspect the camshaft for potential signs of wear and tear.
6. Inspect the Parts
Once you’ve worked on restoring the cylinder head, you’ll want to take some extra time to inspect the rocker arms, valve guides, studs, and other components in the assembly.
With everything open now, it’s much easier to update or fix anything that could be developing. Replace any damaged parts as necessary.
7. Assemble the Cylinder Head
Once all the parts are clean and in excellent condition, you’re ready to assemble everything. Use the same procedure for the disassembly to return the components back to their original location.
If the valves and other components are not in their correct position, the cylinder head won’t work as expected.
Your timing belt or chain might need to follow a specific installation procedure. This information is now always found in the owner’s manual.
You can consult with a tech guide for your make and model or speak with a mechanic about what to do with that step.
8. Install the Cylinder Head
Once the parts are assembled, you can place the cylinder head back on the engine block.
Follow the steps in reverse to remove the head, ensuring to mount each component as instructed. You’ll need to get new oil and coolant into the engine.
Do not attempt to install a component if you’re unsure about where it goes. Consult a guide or an experienced mechanic to reduce the risk of damage.
Should I Invest in 862 Heads?
The 862 heads are an excellent choice for any GM vehicle with an LM7 engine. Although the design is meant for high-performance settings, it performs well in the Avalanche, Express, Silverado, Sierra, Yukon, and other trucks or SUVs from the late 1990s to about 2007.
You know if you’ve got an LM7 engine by looking at the eighth digit of the Vehicle Identification Number (VIN).
The original engine used an iron block to give the engine strength. Upgrading to the aluminum 862 heads encourages a more robust performance while potentially improving your fuel economy.
Are 862 heads any good? Absolutely.
