Cylinder liner flange and flange seat

The cylinder block has circular, plane recesses, called flange seats or counterbores. These hold the cylinder liners in the cylinder block. The flange of a cylinder liner must fit exactly into such a recess, so that the liner rests on its entire circumference on the flange seat. The cylinder head gasket is then placed on the cylinder block. The sealing of the combustion chamber (for older models a metal border, for newer metal gaskets a profiled surface) has to fit correctly onto the top of the liner flange.

When the bolts are tightened, the cylinder head is pressed firmly against the cylinder block. The cylinder head bolts and the tightening instructions are designed to achieve a firm connection between the cylinder head and the cylinder block. This means that enormous forces are introduced from the bolts via the gaskets to the liner flange. This makes it even more important that the forces via the head gasket are transmitted vertically to the liner flange. (Sketch 1 shows correct fitting) 


Sketch 1: Only correct fitting ensures the right transfer of forces.


Sketch 2: Dirt particles under the liner flange—a cause for dangerous flexing moments.


Danger of damage: Inclined force lines

Cylinder liners are made from grey cast iron. This material has many positive properties. However, flexing is not tolerated by this brittle material. When the force lines are only slightly angled through the cylinder liner flange, flexing results in the upper part of the liner that can lead to fracture of the flange.

Common reasons for bending moments

Dirt particles: to avoid contaminations between the flange and seat in the block (i. e. dirt, chips, gasket residue, sealing material, etc.) cleanliness during fitting is important. Also sealing paste should only be used when it is stipulated by the engine manufacturer.

Note: when pre-machined cylinder liners are pressed in, it is a good idea to stop a few millimetres before the block and use compressed air to remove material that may have been scraped off from the gap between flange and flange seat. 



A slanted flange seat causes liner flange fracture. (Sketch 3 + 4).


Uneven surfaces and warpage at the flange seat of the cylinder block:

The underlying reasons for this are increasingly lighter engine designs. The warpage at the component will be worse, the thinner the wall thickness of the block. At the same time, power output, combustion pressures and torques are rising all the time in modern engines. In engines that have been running for 350,000 miles (or the equivalent in running time) warpage can already be excessive enough that the seat in the block should be re-machined. The counter bore re-machining should be carried out on a boring mill or with a hand operated, mobile flange facing unit. Important: the surface must not be slanted (see sketch 3 + 4) and after machining, the sharp edge of the seat surface should be chamfered (about 1x45°, see sketch 5). If there is no chamfer, fracture damage can result (sketch 6).

Note: The specified liner protrusion has to be assured before fitting. To adjust the protrusion, a suitable metal shim can be placed under the flange. When the cylinder block is resurfaced, the flange seats have to be redressed by the same amount.


Sketch 5: Chamfer at the sharp-edged flange seat


Sketch 6: Fracture damages due to missing chamfer.


Wrong cylinder head gaskets:

The wrong gasket can introduce angled force action into the flange (sketch 7), either because the diameter of the combustion chamber border is too small or the gasket has the wrong thickness.

Note: Only use the type of gasket that was originally intended for the engine. 


Sketch 7: Force transfer at an angle due to wrong cylinder head gasket.


Sketch 8: Cylinder head machining: if the grove is not allowed for, the forces are transferred via the fire prevention edge and the liner fractures.


Incorrect machining:

Some cylinder heads, like those for certain Volvo types, have a full perimeter groove into which the fire ring of the cylinder liner projects. The cylinder head and cylinder liner must not come into contact. If the cylinder head is resurfaced due to damage or warpage, the perimeter groove must also be machined by the same amount. Otherwise, there is a risk that forces are not introduced via the gasket but at an angle via the fire prevention edge of the cylinder liner (sketch 8).

Proper measurements must be taken:

Otherwise, it will get expensive: a broken liner will move gradually in the direction of the crank shaft after the engine is started. When the location of the liner break is level with the first piston ring in TDC, the piston ring springs open above the break location. At the next downward movement of the piston it pulls the cylinder liner downwards. The rotating crankshaft can shatter the liner, piston and connecting rod.



A cylinder liner, fractured at the flange due to fitting error.

Broken liner flange
Closeup of the liner flange break

Please view this video that does a great job of illustrating the problems that can cause liner flange cracks and breaks. It's geared towards Caterpillar C15 and 3406E engines but is applicable to all engines that have removable liners.

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