I didn't mention Summit giving us warranty replacement because... well, it didn't seem relevant. We were just trying to get this thing screwed back together and runnign right. The money is really a secondary issue to us. It's more a matter of time and effort and pain in the butt of it all.

Didn't mean to mislead anyone. Was more focused on the "science" side of this as an interesting mystery, not so much the dollars and cents of it.

So if the lifters being in the low 50s instead of ~60, that's a lot? I was paying more attention to the cam being off by ~25 points. That's what really jumped out at me right away.

What exactly does the number MEAN? I take it it's some sort of percentage vs. the harness of the point of a diamond-tipped tool?

 

I had the same problem you had with my 350HO crate engine when I installed an XE274 flat tappet hydraulic camshaft in it.

It wiped a lobe just after break in (after a few days of driving it around). Thought it was a fluke, ordered another XE274 and another set of lifters, this time we left the intake off the car and cranked the motor over to watch the valvetrain do its thing.

Lifters were not spinning in the lifter bore. We put a set of GMPP lifters in and they spun like crazy. Put the comp lifters back in and they barely spun. A few didnt spin at all. You could swap the lifters around into different lifter bores and the "non-spinners" would change everytime.

 

The Rockwell hardness numbers are just relative to each other. The "C" scale (HRC) has 100 points as it's maximum, but you'll rarely find or test any metal above HRC 70, and below HRC 20 you should use another scale like HRB.

Some examples:

Ball and roller bearings and their races are in the HRC 60-64 range. These are designed to take compressive loads and deform or deflect the least amount possible under point or small area loads. This the same type of loading the foot of the flat lifter sees.

There is also heavy sliding of the lifter foot on the lobe, of course, so the high hardness is critical. Most of the load on a lifter foot is concentrated at one fairly small spot, but the cam lobe is loaded all around it's periphery, but with the highest loads on the nose (edit) at low rpm and probably near the beginning and end of the lift at high rpm. Wear occurs from both the magnitude of the load and the duration. Again that's why the lifter foot needs to be so hard.

A file is about HRC 60, and has a hard time cutting a harder surface.

Tool steel cutters are generally in the mid 60's. Titanium nitride coatings (TiN) which are yellow-gold color, have a hardness of about HRC 70. That's why they resist wear so well.

Of course there is no free lunch, so with extreme hardness comes extreme brittleness.

Hardness in the HRC 50 range allows more deformation under high compressive loads, and sliding wear resistance is much less than HRC 60+. Most sliding applications would use HRC 60+ not 50.

A grade 5 bolt is about HRC 30. It has about 100,000 psi yield strength but almost no wear resistance for high sliding loads. It would make a lousy bearing surface.

A forged, heat treated 4340 connecting rod or a good powdered metal rod is about HRC 40-42. An old 1141 steel, non-heat treated "Pink" rod is about HRC 20, which is what plain steel bars, or flats or billets are from the steel mill.

Roller lifter rollers are about HRC60 on the surface, as are steel billet cams (lobes and bearing surfaces). Remember there is rolling contact here, not sliding contact llike flat lifters so the material can be similar on both. Not so with flat lifters. That's why cast cams work well with flat lifters. For extreme applications (Cup engines), the lobe wear surface is something like Stellite.

Enough already...