Usually the clips or retaining rings pop out because you don't have the proper preload.With proper preload the plunger should never contact the retainer.If it plunger contacts the retainer it will pop it out.When setting preload on a hydrualic lifter turn the rocker adjuster to zero lash then 1/4 to 1/2 turn to set the plunger away from the retainer.Make sure the lifter is on the bottom of the cam lobe.Do not reuse the retainer.
The HT2011R lfiters are specifically meant to be installed with zero lifter pre-load (this is as per their instructions). The thinking there is that by removing all the pre-load from the start the lifters never actually pump-up at the higher RPM. This is how I had originally set them up.
I see that CompCams now shows the following in their Adjustment Instructions for the ProMagnum lifters "...Through various testing we have discovered that the recommended lifter pre-load should be set between zero and 1/8 of a turn for optimal performance...", so with these lifter bodies they seem to be pursuing similar approach to the HT2011R lfiters.
I will tell you that my motor easily went to 6500 RPM with these lifters adjusted to zero pre-load and my HE3844AL cam. Once I introduced the slight amount of pre-load to quiet it down the RPM did drop and the motor would not pull as high anymore...so my crude "butt-meter" did validate the whole anti pump-up theory.
Your point about the plunger contacting the retainer is well taken though. Given that I actually pre-loaded these during my last adjustment I'm guessing that the lifters did pump-up and maybe I actually got into a bit of valve-float situation where the retainer no longer captured the plunger in the lifter body.
