Mechanics

Piston Ring Replacement

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How to Replace Engine Piston Rings

An engine's piston rings are used to seal the piston to the cylinder wall during the compression stroke. When a combustion event occurs these rings are forced against the engine block cylinder walls to help contain the energy that is released. Most engine pistons contain three separate rings that perform unique tasks. The first ring or top ring is the main combustion ring that takes the brunt of the force as the piston is thrust downward. The second combustion ring acts as an overflow or secondary confinement ring that aids in the service of the first main combustion ring. The third and final ring is used to control motor oil from entering the combustion chamber and being burned as explosive gasses are ignited. This oil control ring consists of three separate pieces and must be assembled on the piston. Piston rings typically last for the life of the motor, but because these rings are created from very hard and brittle metal they can break causing a failure. Failures can range from low compression, cylinder misfire, scoring of the cylinder walls and burning oil. As an engine ages piston rings wear into the cylinder walls and eventual fail, naturally. When this condition is present it lowers the engine's compression which causes low compression, burning oil and heavy exhaust smells which is the result of an incomplete combustion process.

Anytime an engine has reached its normal lifespan the engine needs to be disassembled and re-machined (rebuilt). This process is not difficult with the proper tools and instruction. (Note: if new piston rings are installed without machine work it will make the situation worse due to the oblong wear pattern the cylinder walls obtain during normal long term operations. In other words, new piston rings are perfectly round with no wear, if they are installed into an oval shaped cylinder (worn) the ring operation failure will be amplified.

Tools and Supplies Needed:

  • Piston ring installation tool
  • Protective eyewear and gloves
  • Motor oil
  • Shop towels
  • Small standard screw driver or pick
  • New Piston Ring Set
To replace piston rings the pistons must be removed from the engine block and replaced (if worn.) Also, for best results the connecting rods should be resized. Piston rods can become "out of shape" due to the extreme force they are subjected to. All piston rings are accompanied by a set of installation instructions, these instructions are used to determine the orientation of the piston ring gap. The location of this gap an important aspect to the performance of the ring.

Step 1


New Engine Piston

Begin by cleaning the piston thoroughly and securing it firmly in vise. (Do not tighten against piston, use connecting rod.)

Step 2


Piston Ring set with Rod Bearings

Next, remove the piston rings from the box and separate them into organized piles on a clean surface, use caution as to not mix rings or turn them over. (Compression rings install one direction only.) Locate piston ring installation instructions and read completely. (Each ring manufacturer has specific instructions.)

Step 3


Piston Ring Installation Orientation Guide

Always install piston rings at their popper orientation, this helps provide a superior seal to the cylinder walls.

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2014-04-09)