The liner appears to be one of the least technical parts of the engine… and yet it is the foundation. Discover its manufacture, its materials, its casting and its arrangement so you can really compare.

The role and stresses of the liner

The liner delimits the combustion chamber: it houses the piston and its rings to allow compression — a bit like the body of a syringe. It can be dry, wet suspended, wet clamped or with intermediate support.

It must meet several criteria: resistance to temperature, bore metrology (ovality, taper, straightness), resistance to corrosion and internal surface finish. For this, various materials are used — lamellar cast iron, spheroidal graphite cast iron, steel, aluminium — combined with various arrangements.

How is a liner made?

Before machining, you need a raw casting. A process is used called centrifugal cast iron : the centrifugal force expels impurities outwards and prevents the formation of porosities (shrinkage cavities).

Beware of the foundry work: a bad casting gives surprises during machining or in use. Below, a raw casting showing porosity marks.

The material: GL cast iron, GS cast iron or steel?

The material: GL iron, GS iron or steel? cast irons and the steels. Today, liners are mainly made of lamellar cast iron, some of spheroidal graphite cast iron; steel is reserved for special uses.

. Today liners are mainly made of lamellar iron, some of spheroidal graphite iron; steel is reserved for specific uses.

Designation EN-GJL…: the numbers give the grade of the cast iron (like the carats of gold). For GL, it is the breaking stress: EN-GJL200 corresponds to 200-300 MPa.

The problem with GL is its structure: the graphite lamellae concentrate stresses, initiate cracks and promote their propagation. Under repeated buckling — and especially with increased turbo pressures — an initiation point can become a complete crack.

GS cast iron, what is it?

Designation EN-GJS… (only one letter changes). What sets it apart is its structure : the graphite is present in the form of nodules (spheres) which stop cracks — like drilling a hole at the end of a crack in a sheet of metal.

Another criterion: the tensile strength, measured in the laboratory on a test specimen. For the best durability, aim for a grade of 700 or 800 — we talk of a structure pearlitic (GS700 or GS800, like gold in 18 or 24 carats).

For nearly 20 years Mespiecesauto has been making liners in certified GS700 cast iron : to guarantee the casting quality, stay transparent, and restore confidence after bad experiences with 'fake' GS that break quickly. Today, some customers run boost of more than 2.5 bar in our liners and, in all these years, none has cracked.

Common point to both cast irons: graphite offers a much better friction coefficient than steel — we even speak ofself-lubrication. The GS700 liner is an 'easy to live with' liner.

The steel liner

In the 1970s, some 'works' competition cars had steel liners; 40 years later, some still offer them. The big problem with steel is its very high friction coefficient : different operating clearances and expansion, and very regularly cases of seizing or of ' scuffing ' (adhesive wear of the piston rings). Hence the expression: 'steel liners eat piston rings'.

In our view, steel is only justified in one case: when the base thickness becomes very thin, below 1.3 mm, as machining GS at the base becomes complicated. But before that, consider all the options (e.g. reboring the block to leave more thickness — on an A310 4-cyl Group 4 block rebored for liners of 87 mm outside / 84 mm bore, versus 77.80 mm as standard). Specific hardnesses (HB) and surface treatments must be respected; you need to know these treatments to choose a compatible piston ring, otherwise destruction is even faster.

Comparison: GL cast iron, GS700 cast iron and steel

Liner arrangements

There are four arrangements; let's focus mainly on the clamped liner.

• (a) Press-fitted then rebored to size: a strong interference fit to prevent it from sliding down (neither bottom support nor top retention).
• (b) Suspended by a flange (top support): the major drawback is the perpendicularity between the lower axis and the flange — otherwise the liner sits at an angle and the head gasket seals poorly.
• (c) Compressed : the most used in the automotive world. Support at the lower part, water/oil sealing provided by an O-ring or paper gasket — the base gasket.

Deglazing the liners

Often considered basic, deglazing (or honing) is nevertheless essential to the proper functioning of the liner–ring–piston assembly. It consists of scoring the cylinder with cross-hatched lines of a defined depth: this roughness retains the oil and creates the oil film.

Two criteria: theangle formed by the lines, between 45° and 55°, and the roughness. Insufficient roughness breaks the oil film → wear of the piston rings or seizing.

The machinist chooses the honing stone according to the material and the diameter. Entrust this step to a professional, otherwise you risk major lubrication problems.

Our GS700 cast iron liners, by model

We manufacture liners in certified GS700 cast iron for many engines:

FAQ — GS, GL cast iron or steel liner