If it was valve clearance, either floating or not checked, then clearly the motor was not 'blue printed'. Blue printing is simply checking and double checking everything, and 'clearance' is a HUGE part of that. As is valve spring tension that matches the cam, and degreeing the cam is as well.
Heres a pic where I'm using modeling clay on top of the piston to check for valve clearance with the cam all ready 'degreed' and the valve lash set. The valve opens, leaves a mark in the clay, you then measure the depth of the indentation in the clay and THATS your valve clearance. Only way to be sure...
I 'dry assembled' my engine numerous times during the blue printing process before I did the 'final assembly'. This is very labor intensive and would cost a fortune if you were building motors commercially. SO, you offer 'package' motors with known specs and known parts so you don't have to double check everything. The problem is, sometimes that works and sometimes it doesn't. 'Blue printing', it's one reason why you pay BIG bucks for a custom built engine and then wonder how apparently the SAME spec engine from another guy is way cheaper. It's all about the 'final assembly'.
Now it's also possible you simply had a defective valve, stuff happens.
