Recommended but optional. IMO change them every 40 - 50k anyway. They might last 80k for all I know, but in my experience 40 - 50k is a good time to change them for any engine. It's only $6 -$15 a plug every 40k and knowing they're good is way better than one or more fouling out and putting you in "limp" mode at a bad time. Not worth the trouble for me, but thats my opinion.
