What is a Catalytic Converter?
A honeycomb filter that chemically cleans harmful gases out of the exhaust before they leave the bike.
Simplified animation — not to scale.
In plain English
Fitted on modern bikes to meet emissions rules, the catalytic converter uses precious-metal coated honeycomb to convert harmful gases into less harmful ones as exhaust passes through.
“A chemical scrubber sat in the exhaust stream, quietly cleaning up after every combustion event.”
How it works
As hot exhaust gas flows over the catalyst's coated surface, chemical reactions convert carbon monoxide and unburnt hydrocarbons into carbon dioxide and water vapour. It needs to reach operating temperature to work properly, which is part of why cold starts are dirtier than a fully warmed engine.
Signs of trouble
- ⚠Reduced performance from a blocked cat
- ⚠Rattling noise from a damaged internal honeycomb
- ⚠Failing an MOT emissions test
- ⚠Sulphurous 'rotten egg' smell from the exhaust
£150–£600
Always get a written quote. Prices vary by bike, region, and parts brand.