Trouble-shooting that grinding feeling in my right pedal

I ride a single-speed bicycle. It's supposed to be smooth and quiet. And yet, it is not.

There is a brief grinding in my right pedal on every other pedal stroke. When I really torque the pedals, it is more pronounced.

I took the machine to the bike shop to see if they had some idea. Was it a bad bearing in my bottom bracket? Perhaps a bad bearing in the pedal? A lose crank? The bike mechanic at my LBS first tightened everything in the neighborhood of the grinding, without either confirming or denying that he felt the grinding.

His efforts produced a tighter, but still grindy, drive train.

Another mechanic came over, a guy I trust, and he said that he thought the chain and chain ring were worn down. He offered to put a $20 chain ring on my bike. I demurred. I resolved to try to fix it myself and promised to bring it back once I had fucked it up, so he could do it right.

We laughed and parted ways, though I could see that he was irritated with me for letting him diagnose and then not paying him to repair. Whatever. Like I want a $20 chain ring. Doesn't he know I'm the modern day Fausto Coppi?

Something about his diagnosis just didn't ring true with me. Why would a worn chain ring produce a grinding sensation only at the top of every second pedal stroke? Chain rings are round. If there was a defect or worn spot, it would produce the grind on every pedal stroke.

I have been thinking about this, literally, for weeks without buying a new set of cranks and a chain ring. I did replace the pedals, but only because the ones I had were a little smashed up from all the times I've crashed that fucking bike.

And so, on the way home last night, I was obsessing about the chain ring and trying to ignore the grinding feeling and it was slowly driving me crazy and suddenly it struck me. The source of the problem is obvious. I have a bad link in my chain. The chain ring has 48 teeth. If the chain has 96 links (which seems about right) that would produce a grinding every other rotation of the pedals. A new chain costs $10.

If I prove myself correct, I am going to celebrate by buying a new chain ring. And probably a set of cranks.