What are Piston & Rings?
The moving plug inside each cylinder, sealed by thin metal rings so compression doesn't leak away.
Simplified animation — not to scale.
In plain English
The piston slides up and down inside the cylinder bore, and the rings wrapped around it seal the tiny gap between piston and cylinder wall. Without a good seal, compression and power both leak away.
“Like a bicycle pump plunger with a rubber seal — if the seal wears out, you can pump all day and barely feel resistance.”
How it works
As the piston rises it compresses the fuel-air mixture; the rings keep that pressure from escaping past the sides. A second set of rings scrapes excess oil off the cylinder wall so it doesn't burn in the chamber. Worn rings let compression and oil past in both directions.
Signs of trouble
- ⚠Blue-tinged smoke from the exhaust
- ⚠Engine burning through oil faster than normal
- ⚠Reduced compression and sluggish performance
- ⚠Rattling 'piston slap' noise when cold
£400–£1,200
Always get a written quote. Prices vary by bike, region, and parts brand.