Interference engine
An engine whose valves and pistons pass through the same space at different moments.
Also called: interference design
What it means
Definition
In an interference design, the valves and the piston occupy the same space in the cylinder at different points in the cycle, with only clearance in time keeping them apart. While the camshaft stays correctly timed to the crankshaft, they never meet. If timing is lost, they can. A non-interference design leaves enough physical clearance that they cannot meet even then.
Why a buyer cares
What it changes
It explains why a shop treats a timing belt or chain fault as urgent on some engines and as a driveability issue on others.
In practice
Where you meet it
In a shop's explanation of why a timing job is being pushed, and in belt application guides that flag which engines are interference designs.
Two things that look alike
Not the same as
Belt and chain are the parts that keep timing; interference describes what happens inside the cylinder if that timing is lost.
Read next
Related terms
Where this comes from
Sources
The definition here is written from what the manufacturers’ own manuals say, but those documents could not be opened and quoted, so nothing is being presented as a citation. How we source data
NO CITABLE SOURCE. This site failed to source the term once before and a second attempt failed the same way: Gates' guides mark interference applications with a symbol without defining the term, and no .gov, manufacturer or standards-body definition was found. Publish through the empty-source path or hold the entry.