Technically, you're not supposed to do this, but can you turn the engine backwards? The chain can get messed up if the engine turns backwards, but it sounds like you might have other problems. Turn it very slowly backwards...
Heck, let me ask: Are you turning it the right direction to adjust the valves? Clockwise is the way to go...
In general, if you haven't done this before, it can be a bit unnerving. Even if the belt is tight, the engine may or may not turn easily (even with the plugs out). The grinding noise (not sure what you mean by grinding) could be the sound of the pistons moving in the cylinders. If you haven't had any problems with the motor, I doubt that there is anything wrong - you haven't done anything, unless someone dropped something in the spark plug holes. You did say that the plugs were out - you can't really turn the SC motors without those plugs out.
Anyways, unless you are turning the motor backwards, everything sounds ok. Unplug the CD box and crank the engine - if it turns, you're fine. If it gets stuck - you're not. I doubt you'll have a problem...
-Wayne
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