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Good idea Southernor. Always better safe than sorry. Also, if you find what cylinder it is, check the rods themselves. Many times a loose rod will cause chipping/scouring on the bottom end. If the...

No. the cylinder wont have the pressure from the the expanding gasses. As such, it shouldnt knock unless your bearing is really, really smoked. From the sound of it, it isnt.

Pull the plug to #2, then #4. If it stops tapping, its the rod bearing to the cylinder thats unplugged, so to speak