Collpitts oscillator signal distorted
Change R3 from 100k to 68k
Change R2 from 147k to 27k thus Rb=20k and Rin= 100k hFE*Re ~100 * 1k
Replace wire with 1k from emitter to C2//C3 to match R1.  

Root Cause:  The C loading Re at some harmonic of 8MHz is causing output distortion.  When there is series C coupling on Emitter always make Rmin load >= Re.  In this case equal.

Expect 2Vpp sine output.  Use another buffer if you plan on driving any significant capacitance ( e.g 30 pf /ft)