Single row timing chain as fitted to every A series engine until the twin row duplex gear set was introduced on Cooper S cars.
Check your timing gears for wear and if need be upgrade to a duplex kit C-AJJ3323.
Please note: the cam gear with the tensioner rings was superseded by the plain gear which is the only type available.
For the simplex timing gear kit, see SIMPLEX
For the crank timing gear, see 8G725
For the simplex camshaft timing gear, see 12G4337