You are trying to remove the timing chain cover. And a harmonic balancer puller has always done the trick for me. I hope you are not trying to use a 3-jaw puller. That is a good way to slip the inertia ring on the balancer.
If you are using A balancer puller and the engine is turning over just put it in gear.
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1988 Mustang GT
11.8 @ 123 (7/14/01)
11.5 @ 120 (9/14/01)
1992 BadAzz Wrangler
1993 Explorer
See my car at:
www.mustangworks.com/cgi-bin/moi-display.cgi?179