Pistons & Piston Rings

Do your cylinders need to be bored out, or does your engine need to handle more boost than it did from the factory? This category brings together pistons, piston sets, piston rings, wrist pins and circlips for rebuilding and building engines – for you who assemble the engine yourself or are planning a bigger project.

Pistons, rings and pins work together

The piston transfers combustion pressure via the wrist pin to the connecting rod, while the piston rings seal against the cylinder wall and control the oil. Circlips hold the pin in place in the piston. You can choose complete piston sets or individual parts such as piston rings and wrist pins. If the bottom end also needs strengthening, connecting rods and bearings are typically part of the same project.

How to choose pistons and piston rings

Start with the engine's dimensions and purpose, then choose based on these criteria:

• Bore and oversize: The piston must match the cylinder's finished size. The range includes, for example, standard size and oversizes such as .020 and .040 inch, and the final size depends on how the block is machined.
• Compression and crown shape: Crown volume (e.g. -14cc or -21cc) and compression ratio affect how much boost and which fuel the engine can run. Valve reliefs may be necessary if you switch to a different camshaft.
• Ring pack: Ring heights such as 1.0 x 1.0 x 2.0 mm or 1.2 x 1.5 x 2.0 mm must match the piston's ring grooves.
• Coating: Some pistons have a coated crown or skirt, which can reduce friction and wear – the effect depends on the product.

In this category you will find Wiseco, JE Pistons, CP Pistons, Mahle and Mahle OE, among others, e.g. Mahle pistons for Dodge 12V and 24V diesel engines. Check piston-to-wall clearance, ring end gap and ring orientation according to the manufacturer's instructions before assembling the engine, and follow the recommended break-in procedure.

Frequently asked questions

Should I use standard size or oversize?

It depends on the cylinder's dimensions after measuring. If the cylinder is worn or scored, it is typically bored out, and the piston is chosen to match the finished size. Have an engine machine shop measure the block before you order.

Can I reuse the old piston rings?

This is typically not recommended. The rings wear in against the cylinder wall, and new rings normally give the best seal. If you replace the pistons or hone the cylinders, the rings should also be replaced.

Why is the ring end gap important?

The rings expand when they get hot. If the gap is too small, the ends can butt together and damage the piston and cylinder. The correct gap depends on bore, use and boost – follow the ring manufacturer's instructions.

Should wrist pins and circlips be replaced along with the pistons?

Piston sets often include pins and clips, but it depends on the product. Circlips should typically always be new, as they can lose tension when removed.