Two cylinders from a 9 cylinder Bristol Mercury - a valve spring is just visible on the LH cylinder. The tyres are from a Bedford truck or BSA motor bike.

Bristol Mercury radial engine - owned by the Aircraft Restoration Company, Duxford

Westland Lysander
Blenheim Bomber
RAF Trolley Acculmulator
Bristol Mercury engine

Bristol Mercury cylinders - owned by the Aircraft Restoration Company, Duxford

Many thanks to the Aircraft Restoration Company engineers who helped me with these identifications, especially Colin, Mike and Smudge.