The chain popped off during about a 4 block ride today.I was just cruising casually.I ridden the bike 4 or 5 times,the longest trip was 10 blocks or so.Having ridden so many times with no problem it doesn't seem like a chain alignment to me,but I am new to this.The rear sprocket and the chain idler are tight and in same place I assembled them.It's a stinger sd kit in a huffy cranbrook.Any and all thoughts appreciated.