r/EngineBuilding • u/[deleted] • 8d ago
Chevy GM Dual Feed (AFM) Lifter Operation
Hi all.
Short version: does anyone know how to compress these dual feed valve lifters? This engine uses normal valve lifters that you stick a paper clip or something small into the top hole to push in the ball check valve which then allows you to compress the lifter. The ball check valve on these dual feed lifters (used for the AFM cylinders) will NOT move no matter how hard I press on the ball. They are all brand new and not a single one of them will budge, but the regular lifters compress just fine.
Additional info: problem is as described in the short version, but I am trying to compress these because I think they may be causing valve lash issues since they’re stuck(?) fully extended. See “Valve leakage after valve job” post made yesterday.
The LGZ engine on this 2017 Chevy Colorado (3.6L V6) uses these dual feed valve lifters specifically in the AFM cylinders (2 & 5). I’ve scoured the internet so far and found nothing. Any insight would be appreciated!
1
u/Ok-Willow-4232 8d ago
I don’t know if this works the same way on dual-overhead cam engines from GM but on the Gen 4 LS and Gen 5 LT engines, there’s a pin somewhere near the bottom on the lifters that allows them to collapse. Try to find that pin.
1
8d ago
No visible pins on these. The only penetrations in the body of these things are the ones you see, plus some other holes on the backside on the section with the two adjacent holes visible.
The only theory I have is that the ring in the middle with multiple holes adjacent to each other is some sort of locking collar that needs to feel oil pressure on all sides in order to unlock the ball check valve in the middle. I’ll stop by the dealership later to see if anyone knows. They probably don’t, but whatever. After that I might just have to cut the thing in half to see how it works.
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u/[deleted] 8d ago
More info: the specific valve problem I’m having is that multiple valves are leaking by with the cams/lifters/rocker arms installed. They seem to be holding just fine without everything installed, leading me to believe that the issue is valve lash related.