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Knocking combustion severely limits the performance and life of spark-ignition engines. Knock damage typically involves surface erosion of pistons and heads, which is thought to result from a combination of shockwave pressure and thermal stresses. This work investigates the contribution of thermal stresses to knock-induced erosion damage by modelling the temperature profile within the walls, using existing thin-film thermocouple data and 1-dimensional transient heat transfer relationships. The temperature profile is then used to establish the thermal stresses through the wall (of the piston or cylinder head). Results demonstrate that knocking combustion causes thermal stresses between 2 to 3 times greater than that of non-knocking combustion. For knocking conditions, tensile and compressive stresses exceed 20 MPa and 90 MPa respectively, with the maximum tensile stresses occurring about 1mm below the hot surface and the maximum compressive stresses at the hot surface.