From experimental tests on a motor grain model it appears that both SIF values and crack geometry during growth are quite variable due to shear modes for the off-axis inclined cracks. The numerical study was to find the SIFs versus crack length for three different configurations: symmetric crack, off axis straight- in crack and off-axis inclined crack. The experimental off-axis straight-in crack remains straight in growth after some minor rearrangements, and Mode I is present. For the off-axis inclined crack, which turns on a curved path, after some limited amount of growth Mode II as well as Mode I remained. The numerical simulation shows a rapid change of direction and presence of Mode I. At maximum depth all the experimental 3-D SIFs were smaller than the numerical 2-D corresponding values. For complete three-dimensional numerical simulations mode III has to be considered.