Over training has a lot of factors:
Me personally I can "feel" when I have over trained. I ache, in a not pleasant way, weight that should feel a bit lighter begins to seem a bit heavier. Etc.
Personally every 4-5 weeks I try to take a good week off. Trust me, it won't kill you.
Some people do 4 weeks of heavy and then a week "off" but during that week they still stay active (1-3 sets, light weight). However all these numbers are meaningless. There is no magic number--hence why everyone does things differently.
Just listen to your body and see what it tells you to do. If still unsure train hard for 4 weeks and then take a week off. Won't kill you...
also, IMO doing chest 3 times a week is ridiculous.