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Cylinder Bore Surface Finishes
Copyright AA1CarAdapted from an article written by Larry Carley for Engine Builder magazine
Cylinder bore refinishing is an integral part of rebuilding an engine. After tens of thousands of miles, the cylinder bores can become
worn, tapered or scratched. Cylinder wear can be accelerated by poor air filtration (such as a missing or damaged air filter element, leaks between the air filter element and its housing, or air leaks downstream of the air filter). Any of these conditions can allow dust and abrasive particles to enter the cylinders where they will cause wear on the piston rings and cylinders.
Poor oil maintenance can also accelerate piston ring and cylinder wear. Not changing the oil often enough or lack of proper filtration can allow abrasive particles to attach the rings and cylinders from underneath the pistons.
Cylinders may also be damaged by broken piston rings or by wrist pin retaining clips or wrist pins have have come loose.
When the engine is disassembled, the condition of the cylinders must be inspected to determine the extent they are worn. A cylinder bore gauge can be used for this purpose. Measurements can be taken at various locations from the top to the bottom of the cylinder. Wear will always be greatest at the top of the cylinder where cylinder pressures and temperatures are highest. This is called taper wear. If taper exceeds specifications, the cylinders need to be bored to oversize to restore straightness.
Which type of cylinder finish is best?
The best cylinder bore finish is one that provides a good sealing surface for the piston rings, minimizes blowby while also retaining oil for proper ring lubrication. The cylinder bore finish will depend on the type of rings used, the type of honing stones used, and the boring and honing techniques used to finish the cylinder bores. Surface finish parameters and techniques to optimize the finish and reduce bore distortion are all covered in this article:
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