Chain broke. Who to blame?

[kokis]

I had RK 520 WX chain installed. Worked fine for 1.5k miles and today it broke. I will post pictures tomorrow. It broke at master link. Master link came out from both sides and both ends for some reason. I could not find broken pieces to inspect. One roller at broken end is wry with it's pin. It happened at hard acceleration. I do a lot of hard acceleration and 300miles ago at regular chain clean\lube there were nothing suspicious. After chain was installed I checked master link to make sure it is not over-tight and can move up and down with out stalling. I don't polish my chain everyday, just doing cleaning and lubing with generic silicone lube. If I hold chain I can move links up and down and I would not say they come back to their position freely but I can move them easily.
Is it incorrect chain installation or bad product or bad maintenance?
Fortunately no one was harmed and I have replacement from DID.
Bike is 14T M696.

[Raux]

whoever installed is to blame IMO

[BK_856er]

Assuming it was a rivet type master link, and if I understand your description correctly, it sounds like the pins were not peened over enough at install.  Don't know how else the whole link could fall out and disappear.  Sometimes stuff just breaks, but those are low miles on a low HP motor.  Not sure there could be anyone to blame at this point.  14T sprocket adds stress to the chain, but it's a common mod.  Be grateful you didn't smash up the engine case!

BK

[seevtsaab]

I think the links should feel fairly firm as you describe? I'd imagine if not you'd feel a lot of 'lash'.
But I'm no expert, I just busted a chain on my 620 with ~7K on it.
I had re installed the stock 15T for a trip and like it.
Years ago I had installed the DT engine guard. No issues wiht 14T turns out with 15T there was contact with chain.
Lucky I was on my dirt road in first, it was probably the shit washboard I was on that finished the failure.
Chain caught between rear sprocket and swing arm and the wheel locked. would not be fun at speed on pavement!
Oh yeah pushing the bike home 1/2 mile uphill - not fun either.

You can bet there's clearance now.

[ellingly]

Under or over peened ends. Hard to say without looking though. Most people, in my experience, overdo rivet links rather than under do them.