Cavity ring-down (CRD) absorption spectroscopy is applied to study predissociation of the CH B(2)Sigma (+) v' = 0, N' = 17-19 and v' = 1, N' = 9-11 rotational levels in a low pressure methane/air flame. Collision-free lifetimes from broadened spectral lineshapes are 45 +/-6 and 10.0 +/-1.5 ps for CH B(2)Sigma (+) v' = 0, N' = 18, 19 and 75 +/-15, 15 +/-2 and 5 +/-1 ps for CH B(2)Sigma (+) v' = 1, N' = 9-11. These lifetimes are in good agreement with previous calculations by Wyel theory using potentials calculated by the iterative Rydberg-Klein-Dunham method [N. Elander, et al., Phys. Scr. 20 (1979) 631]. Experimental results suggest that the F-2 spin-orbit levels might predissociate slightly faster than F-1 levels.