Broken valve spring retainer

[bigirb2002]

We cant figure out how this happened. 1 day it felt like the bike lost about 10 percent of power around 9k but she still got down nicely. There was a faint tapping. The tapping got louder to the point I decided to tear her down to see what was going on. I found a cracked retainer and cap. Valve did not drop or contact piston. Valve is straight and not bent still holding well. Any idea how this happened? Everything else looks great and valve lash is in spec.

 

[bigirb2002]

Forgot to mention stock engine

 

[Kiwi Rider]

Wow. Good thing you pulled it down for inspection and found that damage before the valve dropped and created mayhem.
Looks like a massive impact on the valve must have caused the crack in the retainer and it carried through to the bucket and cracked that as well.
I wonder if a foreign object got caught between the piston and that valve as the valve was open and the piston on it's way up.
Hard to say without looking at it for further evidence to support my theory.
Is there any witness mark or marks on the piston crown?
Or . . has the spring failed in some way stopping the travel of the valve suddenly, and the shock has cracked the retainer and bucket?
Yeah, it's a tough one to nut out.

 

[Kiwi Rider]

Forgot to mention stock engine

So the head has never been off before?

 

[Kiwi Rider]

Forgot to mention stock engine

Has anyone ever set valve clearances on this engine?
If so, Maybe the shim was incorrectly fitted to the top of the valve retainer, on an angle and the bucket fitted and overloading the retainer?

 

[bigirb2002]

Not to my knowledge had the bike a year. I ended up replacing the springs,shim bucket, and retainer. All is fine now

Has anyone ever set valve clearances on this engine?
If so, Maybe the shim was incorrectly fitted to the top of the valve retainer, on an angle and the bucket fitted and overloading the retainer?

Not sure. I did check all clearances before I resealed the engine. They was in spec however cant say much about the valve i had issue with. I can say tho when i put the shim back in it was also in spec with the parts i replaced