collapsed lifters

[edd]

I just had a valve job due to a blown head gasket ,and got bowl blending and Isky valve springs (shot originals) installed, along with Speed Pro 1.6:1 rockers.All was good for about 200 miles when the rockers started ticking. About 20 miles later , I stopped driving it , the noise was too much. I pulled off the passenger side valve cover,and six rockers were fully compressable with just thumb pressure.The other two seemed normal.The driver's side is noisey too , but not as bad.I was hearing periodic tics from the pass side before the big steam-out,but I thought it was the air injector check valve (wrong guess).tThe car is a 95 Z28 with only 93K miles on it.Oil pressure is 18 at idle and 45-50 at higher rpm's.What made the lifters fail?Should the shop have seen the problem as they were adjusting the valves? I am out $2300 and the car is now parked dead.