Flat tappet cams and zinc

[jcisworthy]

I was told by a lifter company a few days ago that zinc oil, or zinc additive in conventional oil, is needed for flat tappet cams because modern oil is too slippery to cause proper lifter spin. He said more or extra zinc promotes surface friction for proper lifter spin.

I have ran flat tappet cams and conventional oil for years with no issues.

What are your thoughts?

[jcisworthy]

I said lifter crown and lobe taper should cause the lifter to spin no matter what oil you have in the engine. He disagreed.

[F-BIRD'88]

Not how the zinc works but if when the crown wears off the lifter it will no longer spin.

Kind of a chicken or egg thingy.

[jcisworthy]

If the lifter is spinning and well lubricated, should the crown ware off?

[Walter R. Malik]

"to slippery" ... I don't think so.
Although, that is a way to explain it from someone who does not really know the chemical properties of what is desirable.

[ClassicRob]

The zinc is a softer metal that bonds to the surface which protects the part that needs protection. The forces that push the surfaces together can push the oil away which is why a heavier protection barrier (zinc) is needed.

At least that’s how I understand it.

[MELWAY]

If the lifter is spinning and well lubricated, should the crown ware off?

It does at some point in its life.
I have raced a flat tappet cam in a boat and we tried a different oil every season and inspected cam and lifters
At year 3 I tried royal purple HPS oil and it pitted and flatten most of lobe noses and the lifters became concave against a straight edge
I said ahh well and put them back in a switched back to a high zinc convertional oil the engine would have another 5-6hrs run time on it and still going ok

[jcisworthy]

After losing a flat tappet cam, I do not have to worry about it again because I switched to roller cams and I will never run another flat tappet cam in anything

He said it sounded like an oil problem and I said if it spins and is getting oil on a very mild cam with 275# over the nose and it wipes a cam hard on the break in, I give up on flat tappet cams. It is not worth the worry involved with them for me anymore.

[David Redszus]

Once upon a time, I was asked to investigate what surface finish a flat tappet should have; rough or polished.
I tried both.

The rough surface tappet wore to a smooth finish. The mirror polished tappet surface became rougher
with use. They wound up with nearly the same surface finish.

The "slipperyness" of an oil is due to its viscosity and resulting oil film thickness.

[Truckedup]

I believe Buick Nail heads did not have designed lifter spin... Besides lifter crown, lobe taper, engines I have seen have the lifters offset to the cam lobe...

[MELWAY]

Once upon a time, I was asked to investigate what surface finish a flat tappet should have; rough or polished.
I tried both.

The rough surface tappet wore to a smooth finish. The mirror polished tappet surface became rougher
with use. They wound up with nearly the same surface finish.

The "slipperyness" of an oil is due to its viscosity and resulting oil film thickness.

Is it a catch 22 to think
Is it best to start with a real smooth finish to reduce risk of folding peaks creating tears that could lead to galling or micro welding
Or the coarse finish it better in oil retention during the run in mating period between lobe and lifter

After playing with flat tappets for over 20 years. I have found the Pennsylvanian base stock oils to protect them the best