[rv6john]

I saw this on a track day group and thought it was interesting as I don't remember any similar failures posted here.

The story is that it is a 20k mile track bike that had been "overhauled" once before. The broken valve retainers were found when the the head was removed for another reason.

There was a theory that it was caused by the previous mechanic. Any thoughts?

 

[FubarRacin]

That's very unusual, I've never seen a retainer break before.

 

[koth442]

Maybe someone had used the "hammer" method to pop out the valve retainers on that overhaul?

 

[billv]

+1 on the hammer method. That could have led to a nick/stress riser and later failure.

Yoshimura sells cotters that are machined on the outside. They claim that they better engage the retainer than the OEMs, which are stamped and rounded. Perhaps the rounding allowed the retainer to sit at an angle or otherwise flex and that led to the breakage. I've always considered the Yoshimura claims to be marketing hype but maybe there's something to them.

Does the pictured head have dual springs?

 

[Spyder13]

Stronger springs installed under stock retainers? Improper adjustment, and the cam was beating on it too long? Never seen anything like that.

 

[Ozsyd600]

That is bizarre. The cotters in the first photo don’t look right. The gap is uneven. Hitting the retainer with a metal hammer wouldn’t do them any good. I’ve used a mallet on a vehicle engine when my valve spring tool was lent out. I wouldn’t use a metal hammer though.