on my single speed commuter, the connect link pictured below, broke apart on the solid side. the side with the removable clip remained intact and I probably rode the bike for a few days before figuring out what the strange sound was that occured under load.

chain is only 6 mos old. it's been cold as ice here all month and the bike stays outside. but I'm wondering if i screwed up installing the link originally. if not, any ideas what caused it. bike is only ridden 10 miles a week.

Given that the fixed end broke, with the clip still in place, I think it's fair to say it's nothing you did.

Without seeing the link itself, and/or the drivetrain it's impossible to say why it broke. It could be a fluke, defective link, or something specific to your bike like bad chainline.

However, just guessing based on what I see all to often, it might be that you're running your chain too tight. Disregard if you already know, but the proper chain tension is no tension for single speed bikes. The chain should always have some working slack, to allow for eccentricity in the sprockets. Ideal is vestigial slack with about 1/4" vertical free play in the center of the lower loop, at the tightest place.

I've ridden thousands of miles fixed gear on chains using that link. I suck at chain repair, changing a chain always takes me way longer than it should, and still have never had a problem with that clip. So they must be pretty idiot proof. I doubt it was cold enough to compomise the steel. My guess would either be a defective link that finally failed or the bike was left somewhere, like a public rack, and something hit the chain hard enough to damage it.


Did the side plate pop off the pins or physically break?

side plate physically broke around one of the pins. see attached pic

I think my tension was ok. chainline not so sure. I didnt ever measure it. figured it pedaled fine and was a short distance beater/commuter. so may be negligence on my part.

2 things: Nothing is perfect, & metal fatigue happens ..

Fluke! Nothing you did. Probably will never happen to you again. KMC links are pretty solid, but once in a long while, a defect sneaks through.
There used to be a representative of KMC that hung out on this forum, but I haven't seen him post for a while. I would go to the contact section of their web page and send them the picture, and maybe a link to this thread.

This is an overload failure. It's either a fluke (defective link) or tension overload. When you set up the chain next time be 100% sure that there's ALWAYS slack. You have to check for a few pedal revolutions, and make sure the lower loop sags all the way around. The sprockets are usually slightly eccentric so tension will vary, and if both are eccentric, you want to pedal enough times that the random combination of both having the high spots opposite has a chance to come up.

OR simply find the tightest position based on crank position, and make sure that there's that 1/4" each way (1/2" total) free play in the middle. That will allow enough margin for error for any eccentricity in the rear sprocket.

You might also check chainline, by standing behind the bike and sighting down the upper loop like a rifle.