5.3 liter active lifter replacement.


New member
I have a 2013 Sierra 1500 with the 5.3 Active Fuel Management system. I'm replacing the active lifters on cylinders 4 & 6 (for now) and bought ACDelco parts which I got from Rock Auto. The box that the lifters came in list the GM equivalent part number along with the ACDelco part number, which happen to be the same: 12680871.
In comparing these new ones with the existing ones from the engine, the effective length is about .056-.060" shorter. I did this by placing a push rod into the lifter and measuring from lifter roller to push rod end. I used the same push rod in both measurements.
I'm not familiar enough with hydraulic lifters to know if this matters. Is this relaxed length a non-factor? The lifter will "grow" once it is in the running engine and oil pressure is applied. That's my understanding. But not sure if this is true. (BTW, the parts do not look exactly the same. The internal piston component of the active lifting feature looks different, but that's no big deal in my opinion.) Can anybody educate me on the basics of the hydraulic lifter design and whether or not the "relaxed" position matters?