Piston Rings

Is your engine losing compression, or are you building it up with new pistons? Piston rings seal between the piston and the cylinder wall, control the oil and carry heat away. In this category you will find ring sets in both metric and imperial sizes for when you are rebuilding or building up an engine.

What piston rings do

A typical ring set consists of a top compression ring, a second ring that both seals and scrapes oil, and an oil control ring. Together they hold the combustion pressure in the cylinder, limit oil consumption and transfer heat from the piston to the cylinder wall. Worn rings can cause lower compression, increased oil consumption and more blow-by into the crankcase.

How to choose piston rings

The ring set must match both the piston and the bore. Look at:

• Bore: the diameter of the ring set, e.g. 81.00 or 81.50 mm, must match the finished bore size of the cylinder – also after overboring.
• Ring heights: the heights, e.g. 1.0-1.2-2.8 mm or 1/16-1/16-3/16 inch, must match the piston's ring grooves.
• Quantity: some sets cover one cylinder, others several – check the product description.
• Application: boost, nitrous and operating temperature typically affect the ring gap requirement.

In this category you will find ring sets from e.g. JE Pistons, Wiseco, CP Pistons, Mahle and Mahle OE. If you buy a complete piston set, the rings may be included, so check the contents first.

Installation and ring gap

The ring gap is measured with the ring placed square in the cylinder and adjusted if necessary with a ring file according to the manufacturer's instructions, which depend on bore and application. Too small a gap can cause the ring ends to butt together when the engine gets hot. Install the rings the right way up, stagger the gaps according to the instructions, and use a ring compressor during installation. The cylinder wall typically needs to be honed so the new rings can seat. If you need other parts for the same job, you will find them under pistons and piston rings.

Frequently asked questions

Can I reuse my old piston rings?

It is typically not recommended. The rings wear in against the cylinder, and once the engine is taken apart or the cylinder is honed, they rarely seal tightly again. New rings are therefore normally a standard part of an engine rebuild.

How do I find the right ring gap?

It depends on bore, ring material and application, e.g. boost or nitrous. Follow the ring manufacturer's instructions, measure with the ring placed in the cylinder, and only file if the gap is too small.

Why does the engine use oil after replacing the rings?

During the break-in period, oil consumption can be slightly higher while the rings seat. If it continues, the cause can be e.g. incorrect honing, rings installed upside down, incorrectly positioned ring gaps or wear elsewhere in the engine.