I recently came across some NOS GM 235 Hydraulics with 2 different part numbers and am wondering if they are interchangable. The P/N's on the boxes are 5231830 (HL-31) and 5231450 (HL-18). Some of the lifters have the GM HL designation etched on their sides. Side by side, they are the same with the exception of the color of the push rod seat: The 5231830's have a copper-bronze tint color while the 5231450's do not. Both appear to have the same amount of spring resistance while pushing down on their seat's. From what I have learned so far, the 5231830 lifters were for late 235's (59 - 62) while the 5231450's were for earlier engines. The engine I am rebuilding is a 62. I understand that the current production of hydraulics should not even be considered because of quality problems. I see mixed opinions on hydraulic vs solids in the various posts here. I need to make a decision soon on what kind of cam to run as my engine builder is now at this point. I see Clifford ($$$) offers both cam choices, while Patrick's offers only solid's. I like the idea of "maintenance free hydraulics" but don't know if they existed even with GM OEM lifters. I remember years ago working on my wife's (at the time) 67 Camero with a 327. The engine needed frequent adjustments to keep the hydraulics quiet. Thanks in advance for your responses....
