approaching timing belt change time

I'm approaching 75,000 miles on my jdm h22a, and I was wondering, if the timing on my engine is off, (say b/c of belt stretch or skipping), would that cause my engine to knock? and also, where can I find a knock sensor for cheaper than $40+, or should i just pull 1 from a junkyard? my external coil problem from the h23 is starting to show, it cracked the sensor plug(not completely broke) and the plug wiggles around in place