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The Importance of Liner Protrusion

What is the purpose of liner protrusion?

Liner protrusion is the distance the cylinder liner sticks above the deck surface of the block. The main purpose of cylinder liner or sleeve protrusion is to give you the proper amount of "crush" on your cylinder head gasket. This ensures that once torqued, your cylinder head crushes the gasket evenly and to the correct specification.

How do you measure liner protrusion?

It is important to measure the liner protrusion in multiple locations around each cylinder. It also helps to know not only the spec for protrusion, but also the variation allowed. So on a 3406 Caterpillar, for example, the specification for liner protrusion is .001-.005" (.025-.127 MM). The allowable variation is .001" (.025MM). This means if you measure one cylinder in 5 or 6 places around the cylinder and you are within .001 of each measurement AND your measurement falls within the  .001-.005" (.025-.127 MM) range then you are within spec needed.

You want these measurements to remain consistent concentrically around each hole, but also from cylinder to cylinder. If you are not consistent from cylinder to cylinder, your head gasket might be crushing or sealing properly on one side of the engine and not sealing on the other.

In engines where the liner uses o-rings, it's best to "dry fit" the liners in order to get an accurate measurement. Without the o-rings installed, install the liner into the block and then measure the protrusion. The reason for this is that the o-rings tend to "pop" the liner up out of the hole. Unless you can properly clamp the liner in place to measure the protrusion, the dry fit method will give you the most accurate results.

Engines using a dry liner can be a little trickier. It is recommended to use a depth micrometer first to measure the depth of the counter bore (distance from the deck surface to the flange seating surface in the block). Write this measurement down and now measure the thickness of your liner flange. Subtract the two numbers. This will give you what your protrusion "will be" permitting the liner sits true in the block.

The reason for doing these measurements prior to installing the liner is because in dry liner applications you have to use a sleeve installer or liner press to install them. Once installed, it is difficult to remove them. After they are installed it is good practice to measure the protrusion again. Making sure that they are within spec and consistent cylinder to cylinder.

What are the consequences of incorrect liner protrusion?

Not having the correct protrusion can result in catastrophic engine failure. I have seen everything from a leaky head gasket to a cracked liner flange, to damaged pistons & cylinder head decks. All because someone neglected to measure the protrusion. Below are some examples from an independent lab where an analysis was done on various cylinders and cylinder components.

(Note: The color has been removed from these photographs for better contrast in the illustrations)

Good Liner Flange

The above illustration shows the underside or contact side of a cylinder liner flange. Note the "even" and consistent seating pattern.

Bad Liner Flange

The above illustration shows the underside or contact side of a cylinder liner flange. You can see where the seating pattern is uneven. This is due to inconsistent or out of spec liner protrusion. This improper liner protrusion resulted in a cracked liner flange.

Blasting Media Under Liner

The above photo (under high magnification) shows the presence of compressed "media". After discussions with the engine owner we found out that the block was recently replaced. They had purchased it from a salvage yard that had media blasted (shot blasted). After material analysis was completed the embedded particles were determine to be a different material than the liner itself. The engine owner had not cleaned the media blasted block in a hot tank or steamer to remove debris from the block. When installing the cylinder liners, they had trapped media under the flange.

This resulted in improper liner protrusion and a cracked liner flange. This is an extreme case, but can happen with any foreign debris from steel shot to sand to dirt. This is why it is crucial when assembling an engine to keep it clean!

Bad Deck Counterbore

The above magnified photo shows heavy striations on the underside of the flange. Note the pattern is opposite the machine marks of the liner itself. These striations were caused due to the engines liner seating surface being aggressively machined utilizing a hand operation. In this case a high speed abrasive surface preparation disc. The uneven pattern caused such inconsistencies to where the liner flange was completely snapped form the liner (see below).

Broken Liner Flange

Quite often when speaking with end-users who have fallen victim to the "broken liner flange" or "cracked liner flange" scenarios they are unfamiliar with liner protrusion. When asking "What was your liner protrusion measured at?" seldom do they fire off a "I measured them all and they were .001 to .002 on all of them". Rather I receive questions or silence. It's important to educate yourself with how important liner protrusion actually is and how it is measured so that you do not fall victim to such circumstances.

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