Lifter re-ginding or turning

[Hotrodpaul]

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]

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

[L78steve]

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]

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&quot; 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]

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

[Hotrodpaul]

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]

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

[Lynn]

Do some internet searches on this. I have seen 24, 35, 70 &amp; 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: &quot;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.&quot;

[VintageMusclecar]

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 <span style="font-weight: bold"><span style="font-style: italic"><span style="text-decoration: underline">MUST BE</span></span></span> 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 &amp; forth in the engine while running--definitely <span style="font-weight: bold">NOT</span> 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]

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

[Dusk Blue Z]

The latest issue of Hot Rod Magazine has a tech article about cams and lifters, both curves and tapers. I have not read it yet, just a passing glance in yesterday's mail.
Mike

[Hotrodpaul]

Just checked some this morning. Results:

GM NOS - .0015&quot; crown (100&quot; R)

Crower Aftermarket - .0020&quot; (62&quot; R)

Used GM Solid - .0005&quot; - .0008&quot; crown

So it seems the claim of original GM at 120&quot;R could be correct.

Next step is to program and try a re-cut.

Paul

[L78steve]

Just the (constant) load of the oil pump is enough to keep the cam pulled rearward in the block.

[SuperNovaSS]

This sounds like an awesome experiment. I'm excited to hear the results.

[kwhizz]

From the center (high point) to the outer lip there should be .0021 difference.........That is with a standard dia lifter.........don't think you can get the micro polish required by turning and polishing.......I'm sure GM uses some sort of a orbiting lapping procedure.....

Ken

[Hotrodpaul]

A .0021&quot; difference in heights yields around a 60&quot;R. It appears from the lifters I have seen the face is ground with some sort of orbital wheel while it is being swung on the radius, all while the lifter is rotating. I think a 60&quot; radius would be a good place to start with this experiment.

I have read where it is recommended to polish the new lifter face with 600 grit paper to aid in break in.

The only unknown is the turned finish I will get with the carbide tooling and if polishing can give a finish comparable to the stock lifter.


Paul

[earntaz]

I think this is going to get interesting ... TAZ <<GRAEMLIN_URL>>/dunno.gif

[VintageMusclecar]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: L78steve</div><div class="ubbcode-body">Just the (constant) load of the oil pump is enough to keep the cam pulled rearward in the block. </div></div>

If that were the case there would be no need for a thrust plate or thrust button on an engine equipped with a roller cam.

[L78steve]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: VintageMusclecar</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: L78steve</div><div class="ubbcode-body">Just the (constant) load of the oil pump is enough to keep the cam pulled rearward in the block. </div></div>

If that were the case there would be no need for a thrust plate or thrust button on an engine equipped with a roller cam. </div></div>

Exactly. Unless there is a remote oil pump installed. Think about it the angle cut of the pump/Dist. drive gear will thrust the cam rearward.

If I'm wrong please tell me why.

[Hotrodpaul]

It may be that during extreme engine de-acceleration, such as a shift, that the cam may walk forward when using roller lifters, as the pump may be driving the cam during that very short period. I would think otherwise driving the oil pump would be enough to keep it in contact with the thrust face.

Paul

[earntaz]

With roller lifters you would expect to use a thrust plate of some sort ... TAZ

[VintageMusclecar]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: L78steve</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: VintageMusclecar</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: L78steve</div><div class="ubbcode-body">Just the (constant) load of the oil pump is enough to keep the cam pulled rearward in the block. </div></div>

If that were the case there would be no need for a thrust plate or thrust button on an engine equipped with a roller cam. </div></div>

Exactly. Unless there is a remote oil pump installed. Think about it the angle cut of the pump/Dist. drive gear will thrust the cam rearward.

If I'm wrong please tell me why. </div></div>

Straight from COMP cams (http://www.compcams.com/Pages/412/general-motors-technical-info.aspx) (emphasis added)

<span style="font-style: italic">&quot;Roller Cams

Several points must be considered when installing a roller cam in an earlier block designed for a flat tappet cam. Flat tappet cams are ground with taper on the lobes to force the cam to the rear of the engine. Roller cam lobes are ground flat, <span style="text-decoration: underline">so a thrust button must be used to keep the camshaft to the rear of the block.</span>&quot;</span>

Additionally:

<span style="font-style: italic">&quot;When installing a hydraulic roller cam in an early model block, it is necessary to use a special hydraulic roller lifter with a link bar assembly to keep the lifters from rotating in their bores. In addition, appropriate- length pushrods must also be used. A roller lifter, being physically longer, has a pushrod seat that sits closer to the rocker arm than a flat tappet lifter pushrod seat –necessitating a shorter pushrod. <span style="text-decoration: underline">A thrust button is required to keep the cam from “walking” forward in the block.</span> A wear plate is also a required (though inexpensive) part, which serves to prevent the rear of the camshaft gear of the timing set from excessively wearing the engine block as it works to keep roller cam walk under control.&quot;</span>

The oil pump gears <span style="text-decoration: underline">will not</span> keep the cam pulled back in the block.

I'm really not trying to be argumentative, I just don't want to see anyone get tripped up on a build over erroneous information. If you try to run a roller cam w/o some means of thrust control (either a plate, button, or a belt drive which uses thrust shims), the cam <span style="font-weight: bold">will</span> move in the block during operation and the results will probably be catastrophic.

Think about this: all modern engines that came from the factory with a hydraulic roller cam have some form of thrust control--in `87 when the original SB Chevy went to HR cams they also added a thrust plate behind the cam gear. If the oil pump drive was sufficient to keep the cam from walking, why would they (GM) have went to the trouble &amp; investment to make the thrust plate and all the requisite tooling changes if it wasn't needed?

[L78steve]

The taper ground into the lobes is for lifter spin. I may have a secondary effect of pushing the cam back I don't know.
The reason I believe this is that every cam (flat tappet) Ive installed with a button never made any contact with the cover after disassembly many runs later. The clearance set was the gasket thickness. So I have assumed the cam was held rearward by pump load.
Roller is another issue the plate is needed for insurance that the cam will not walk.
Don't mean to be a PITA just info gathering.
Also i have seen blocks run with high pressure pumps worn from the cam gear contact surface.
Pumps put one hell of a load on the cam gear. You can feel it when pre-lubing. Also oil pumps are loaded weather spinning up or down in RPM.