Conversation so far:
is there a timing belt in a diesel engine
A diesel timing belt very closely resembles a timing belt for a gasoline powered engine.
what is the function of a timing belt
A timing belt is a part of an internal combustion engine that synchronizes the rotation of the crankshaft and the camshaft.
where is the timing belt located
In the internal combustion engine application the timing belt or chain connects the crankshaft to the camshaft.
what does a timing belt look like
A timing belt is usually a toothed belt—a drive belt with teeth on the inside surface.

Question: when is the belt replaced
Self-contained rewrite: when does the timing belt need to be replaced