Your guess??

[Caparco]

Very young engine, out of the blue I hear pinging and rattling! Oil shooting right out of the breather cap!
Now I have a loose valve side to side and up and down, what do you suppose happened,
I've always used good fuel

[Chryco Psycho]

Could be a number of things , the valve guide might be too tight causing the valve to stick open & the guide may have moved or broken , the piston could have hit the valve breaking the head off or bending it if it is stuck open.
The valve seat could have fallen out if hardened seats were installed again causing possible piston contact .
I have also seen where the rocker shaft is overtightened causing the rockers to seize on the shaft holding the valve open .
Either way you have a problem with the head  , broken or a bent valve , damaged valve guide or a dropped valve seat so the head has to be removed to examine .
Fuel has nothing to do with the problem , the compression in the cylinder is probably coming up the guide & pressurizing under the valve cover casing oil to come out of the breather .

[Caparco]

Excellent reply psycho!! I expect nothing less from you!
What a setback this is for me, the engine builder for sure needs to stand behind this one, still well under warranty.
Thanks again ,wish me luck

[Chryco Psycho]

Let me know what you find , I hope your builder is honest .

[mopar jack]

flat cam lobe?

[Daveh]

Hard to tell without hearing it but I had a nasty tick in my 340 and it ended up that the round tip on the end of the pushrod fell off and was making an awful tapping becuase of the additional clearance. 

I'd go with Neil's suggestions first.  He's never failed me yet.  Good luck.