Knock Sensor Removal Trouble

[wats218]

Winterized the boat about a month ago. Drained the exhaust manifolds and port side block plug, pulled the thermostat, and then ran 5 gallons of rv antifreeze out of a bucket through the entire engine. There was definitelt]y red antifreeze coming out of the exhaust.

I've been doing some reading on this site and it seems that everybody removes the drain plug on the starboard side of the block as well. Since I use the cheap rv antifreeze, I figured I'd do the same just in case the antifreeze was diluted too much. On my engine, this drain plug has the knock sensor on it. I got a 7/8" wrench and started turning the knock sensor to remove it. My problem is that the center hex head spins, but the outside housing and the threads in to the block do not. Is there a trick to removing the knock sensor? Did I damage it? The center hex does not spin smoothly, more in rough steps. Below is a link to skidim for the knock sensor that I have.


http://www.skidim.com/prodinfo.asp?number=R020027