- The engine should be cold before removing the head. When the head is bolted to the block, it forms a rigid unit. Unbolting a hot cylinder head (especially aluminum) can cause parts to warp.
- It a good habit to unbolt the head in a direction oppostie to the normal tightening sequence. You can often leave the carburetor and manifolds bolted to an inline head during a head gasket repair.
- To start cylinder head removal, remove the valve cover or covers and disassemble the rocker arm components. When removing the rocker assembly, check the manufacturer's manual for specific instructions.
- After removing the rocker arm and pushrods, check the rocker area for sludge. Excessive build up can indicate a poor oil change schedule and is a signal to look for similar wear patterns on other components. When removing the cylinder head, keep the pushrods and rocker arms or rocker arm assemblies in exact order. Use an organizing tray or label the parts with a felt-tipped marker to keep them together and labeled accurately. This type of organization aids greatly in diagnosing valve-related problems. Also, carefully check the lifters for dished bottoms or scratches, which indicate poor rotation.
- The cylinder head bolts are loosened one or two turns each, working from the center of the cylinder head outward. This procedure prevents the distortion that can occur if bolts are all loosened at once.
When loosening clylinder head bolts, work from the center bolts to the outward bolts in a rotational pattern.
- The bolts are then removed, again following the center-outward sequence. With the bolts removed, the cylinder head can be lifted off.
The cylinder heads of a typical late-model V-6 engine.
- Inspect the old gasket. The old gasket may provide clues to potential engine problems.
- The cylinder head gasket should be saved to compare with the new head gasket during reassembly.
- Carefully match a new gasket to the old one or to the block and head to be sure it is the right one.
- Check for warpage. Use a straightedge across the mating surfacr and slide a feeler guage between the surface and the straightedge. Check for warpage both lengthwise and widthwise. If specifications are not available, a rule of thumb is 0.001 inch per cylinder for maximum lengthwise warpage. A V-6 with three cylinders per head would have a maximum warpage of 0.003 inch. The maximum widthwise warpage would be 0.002. These specifications are combined specifications for both the head and the block. If the warpage is excessive, the cylinder head mating surface muct be resurfaced.
If the cylinder head or block deck must be machined, remove only enough material to restore the flatness. Removing too much material may result in valve-to-piston interference. In addition, on V-type engines, the intake manifold bolts may not align properly after the cylinder head is machined.
- Head gaskets have small holes that control the flow of coolant in the head. These should not be cut out to match the old gasket. If the cooling and oil holes do not match up, serious lubrication or cooling problems can result.
Some head gaskets have coolant metering holes.
- Sometimes gaskets have an imprint marked top or front.
Some head gaskets are printed with installation directions.
- Some V-type engines have head gaskets that interchange from side to side. Others do not.
- Some manufacturers have used different head gaskets for the same size engine built in different years. Use of the wrong gasket in one of these engines can result in cooling problems.
- When reinstalling the head, be careful that nothing is accidentally pinched between the head and the block.
This ground strap was clamped between the head and the block during a careless installation.
Before reinstalling a cylinder head, use a suction gun or air nozzle to remove any oil or water from blind head bolt holes. Failure to do this can result in a cracked block next to the bolt hole. The water or oil will not compress during torquing.
- Installing a head gasket correctly will help guard against combustion leakage.
- Chase the bolt holes with a tap.
- Wire-brush the bolt threads and the underside of the bolt head.
- Oil each bolt with 10W-30 oil and wipe off the oil with a rag.
- Install the head gasket and cylinder head.
- Head bolts should be torqued in the sequence prescribed in the manual. This torque pattern ensures that the head will be pulled evenly against the head.
Head bolts are torqued in a prescribe sequence.
No-retorque gaskets are available for most engine application. However, many imports and older engines require the cylinder head to be retorqued. This is required because the original set of the gasket occurs after initial engine operation and then relaxes. This causes the clamping pressure to be decresed. Retorquing the bolts will reset the pressure.