Lifter re-ginding or turning

**Hotrodpaul** · #1 08-09-2016, 03:03 PM

Does anyone know what radius the factory GM lifters are ground on?

I was thinking of turning and polishing used GM lifters on my CNC lathe. I will post some pics of the progress.

As expensive as the solid lifters are, refacing might be an alternative. I can also drill the face with an .024 -.031" drill for extra oiling.

Paul

**earntaz** · #2 08-09-2016, 03:42 PM

But what about the curvature? Some lifters are slightly convex ... TAZ [img]<<GRAEMLIN_URL>>/dunno.gif[/img]

L78steve · #3 08-09-2016, 05:03 PM

Don't waist your time polishing. It wont work. I tried to save an original L78 cam with new polished lifters and lost 3 lobes.

**Hotrodpaul** · #4 08-09-2016, 05:05 PM

Yes, they are ground with a convex face and the cam has a slight taper so that the lifter will rotate. As the lifter wears, the face will become flat or even concave, and at that point, the lifter/Cam combo won't last much longer. Since I have access to a CNC lathe, I can program a convex radius and re-machine the face to be used with a new or nicely used cam. This is a big problem with original flat tappet GM cams as they tend to wear quickly even with stock valve springs. My survivor 69 Z-28 had some concave lifters after 44K miles with the tops of several cam lobes starting to wear. I plan on trying to re-machine used lifters and see how they work. I had heard the lifters were ground on a 12-18" radius but need some verification. I could measure some new GM lifters on a surface plate with a height gauge to see how much higher the center is than the edge. Then do a cad layout to determine the radius.

Paul

**earntaz** · #5 08-09-2016, 06:45 PM

Good luck Paul -- let us know how this project comes out ... TAZ [img]<<GRAEMLIN_URL>>/biggthumpup.gif[/img]

**Hotrodpaul** · #6 08-09-2016, 09:23 PM

I will measure some NOS GM lifters and let you know what I find. Heck, I may throw one on the CNC, face and polish it to see how it looks.

Paul

VintageMusclecar · #7 08-09-2016, 09:37 PM

Pretty sure OE GM SB/BB FT lifters were ground on a 120" radius.

**Lynn** · #8 08-10-2016, 01:09 AM

Do some internet searches on this. I have seen 24, 35, 70 & 96 (supposedly from Ford engineering drawings of flat head lifters) after just a couple of minutes.

Not sure where everyone is getting their numbers, although I would certainly be more inclined to believe Eric given his expertise. Also ran across this: "NO ONE and I mean NO ONE refaces them with a radius these days.
They are ground with a straight taper. Actually this better matches the taper on the cam lobe."

VintageMusclecar · #9 08-10-2016, 03:28 AM

Different manufacturers used different radii. There are numerous variables that come into play re: the radii, hence the large variances between manufacturers.

A flat tappet lifter MUST BE ground with a radius or it will cause cam/tappet failure. Flat tappet lobes are ground with a slight taper to them to facilitate lifter rotation--no rotation = failure. (side-note: this taper also causes a flat tappet camshaft to be forced towards the rear of the engine while running, which is why there is no need for a thrust button/plate when using a flat tappet cam. A roller profile does not have any taper ground in, and as such the cam would be free to move back & forth in the engine while running--definitely NOT a good situation. This is why roller tappet engines utilize either some sort of thrust plate or a thrust button.)

Anyhow, that and a $5.00 bill will get you a cup of joe @ your favorite bistro.

**Hotrodpaul** · #10 08-10-2016, 12:10 PM

OK, I will measure some GM, and aftermarket lifters and report on my findings. I can also measure the lobe taper on a new or used cam with a surface plate and indicator.

Paul