Liner protrusion and why it’s critical

Updated Nov 6, 2014

piston ringI have talked about liner protrusion many times since I started writing. But most owner-operators who get their engines built by other shops never ask where the mechanic set the liner protrusion.

Liner protrusion refers to how far the cylinder liner protrudes above the spacer plate on the top of the block. If the liner does not protrude enough, the head gasket can, and will, fail.

Proper protrusion, or even a little “extra” protrusion, forms a better seal and helps the head gasket withstand the forces put on it under normal and severe working conditions.

We recently had a phone call from a truck owner who had blown his head gasket shortly after an in-chassis rebuild by a dealership.

He asked us, “Why did it blow?”

We did not build the engine, so we asked him where the liner protrusion was set. He didn’t know, so he called the dealership and asked.

They told him it was “none of his business,” adding that it didn’t matter and he couldn’t change it anyway.

None of his business? This is major! It’s what holds the head gasket, and it is very much his business: It’s his engine and his livelihood.

And, yes, it can be changed. You just have to spend the money for the upper counter bore cutter for every engine that needs the work.

It’s expensive, but so is pulling a head every year to replace the head gasket – especially when they aren’t under warranty.

Cutting the counterbore is the first step in building an engine that will last, and it’s critical.

Ask the shop that’s working on your engine if they have the cutting tool and know the right spec. If they don’t, find another shop to build your engine.

–Bruce Mallinson is the owner of Pittsburgh Power, an engine performance shop in Saxonburg, Pa.