What is a Cylinder Liner?

Lori Kilchermann

A cylinder liner is a device that is pressed into an engine block and houses the piston. It is much harder than the engine block and prevents the piston from wearing through the cylinder bore. Typically used in aluminum engine blocks and diesel engines, the cylinder liner is either pressed into position or held in place by the cylinder head. In large engines such as the engines found in diesel locomotives, the liner is part of an assembly containing a new piston, piston rings and a connecting rod and is changed as a complete unit during scheduled maintenance or repair.

Without a cylinder liner, the cylinder head can become damaged.
Without a cylinder liner, the cylinder head can become damaged.

In aluminum engine blocks, the block material is much too soft to house a piston. The friction of a piston moving up and down inside the alloy block would soon wear out, resulting in a loss of compression and severe oil consumption. The steel cylinder liner is pressed into the engine block and then the engine block is machined to assure that the cylinder head mating surface is smooth and flat. By machining the engine block to receive a steel liner, the engine is able to operate for many years without engine failure.

Improperly sealed gaskets can lead to engine problems, especially in the case of an ill-fitting head gasket.
Improperly sealed gaskets can lead to engine problems, especially in the case of an ill-fitting head gasket.

The flat surface resulting from the machining of the engine block assures a proper seal of the head gasket between the cylinder head and the engine block. An improperly sealed head gasket will result in over-heating of the engine, loss of power, and the potential to ruin the block and cylinder head. Great care must be taken when installing a cylinder liner into an aluminum engine block since the aluminum block will react to heat at a different rate than the steel cylinder liner. Improper fit at installation could result in a broken liner or a cracked engine block.

There are also instances when a cylinder liner can be used to repair a cast iron engine block that has suffered a catastrophic failure to a cylinder wall. Often, when an engine fails or "blows up," the cylinder wall takes the brunt of the trauma rendering it unrepairable by over-boring. In this instance, the block might be machined to receive a liner and then all of the cylinders could be over-bored to the same size, rendering the engine useful once again. For street driven vehicles, this is a viable option which typically offers the vehicle owner a significant savings over the cost of a replacement engine.

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Discussion Comments


I can understand the reservation about replacing a liner in a car, but in a train yard it's just the opposite. We replace liners all the time on a schedule, and it can greatly extend the life of the engine.

This makes sense for a train, though. The engine blocks are gigantic, so there's lots of "wiggle room" and strength is not an issue. Also, trains put on an incredible number of miles every year, so if the engine block was not designed for easy maintenance you'd have to be changing and rebuilding the whole engine block very frequently, and they are not easy to handle because of their size and weight.

People don't really keep cars that long these days, otherwise someone might have developed a similar setup for car engines. Nowadays if you did that the body would rust away and you'd just have a frame with an engine in it.


While I agree that you can use a liner to replace a failed cylinder in an iron block, I have always hated to do it, and I wouldn't have one in my own car.

A big chunk of cast iron like that is a pretty strong thing, but I still would question the strength of it after the cylinder had a catastrophic failure, even with the new liner.

Also, you now have the parts in that one cylinder all new and mismatched from the rest of the moving parts in the head. That makes me very nervous.

Call me paranoid, but I would probably just swap it for a rebuilt engine unless I just plain couldn't afford it


One of the many annoying things about working on a diesel engine is having to deal with the liners in the diesel cylinder head. I get why they are there, but I've always hated dealing with them during a rebuild.

That said, they do make the engine last a lot longer. You can get half a million miles out of a well-maintained diesel engine, and part of that is because they liners increase the lifespan of the cylinders quite a bit.

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