What Causes Piston Ring Scuffing?

Written by joshua smyth
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What Causes Piston Ring Scuffing?
Pistons must be properly lubricated to work. properly (Aeronautical piston engine image by Andrew Breeden from Fotolia.com)

A piston ring is a metal ring that fits around one end of an engine piston. The ring seals the engine cylinder, or combustion chamber, allowing the piston to capture all the power of the combustion occurring in the chamber. These rings operate at high heats, high pressures, and high speeds; as such, they are subject to significant wear. A scuffed piston ring could have several causes, both maintenance- and manufacturing-related.

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Lack of Lubrication

If the engine doesn't have enough oil, the cylinders will not be properly lubricated. As the ring rubs against the liner of the cylinder, dry spots will cause it to scuff. Symptoms of scuffed piston rings include dirty exhaust and excessive oil consumption.

Engine Dry Starts

If an engine has sat idle for even a short time, it may have a "dry start" when next used. This occurs because the existing lubricant sheen in the engine has dried up, and these dry parts of the engine run without lubricant in the first few seconds after the engine starts before lubricant is fully circulated. If an engine is dry-started after a new piston ring is installed, scuffing could result. To avoid this, lubricate the ring before installing it or add a secondary engine oiler that squirts oil into the engine before start-up.

Liner Surface Glaze

Engine cylinders that are overheated by insufficient lubrication can break down the little bit of oil that is present, which then accumulates as a glaze on the interior of the cylinder. This glaze can scuff the edges of a piston ring as it scrapes by, as the glaze won't allow oil to flow properly in the cylinder. Getting rid of this may require a professional reconditioning of the cylinder.

Liner Roundness Faults

If the liner of a cylinder is uneven, some points will rub against the piston ring and cause it to scuff. Here, too, a reconditioning of the cylinder may be necessary.

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