i lost all exhaust lobes on a cam during break-in a few years ago. i live in memphis and the car wasnt far from comp so i pulled it and took it over there. they checked it out and it was "soft". they couldnt explain why the exhaust lobes were the only ones to flatten. one of the comp guys came over to the house with me and we put it in and i did the same exact install procedure which i had done numerous times and he said that the way i did it was perfect because i was reading it straight out of a comp cams install guide. he told me it wasnt uncommon for some cams to not harden correctly. in other words that particular cam missed a step in the hardening process or was rushed thru.

 

Hi, been there done that!
However it was not my motor, nor did the owner listen and take it apart put new bearings. Second cam was put in wiped the bearings on the third pass and scored/wiped another cam. It was also a comp cam.
fwiw, take it apart clean and put bearings in!

 

Another possibility is that the lobe and LSA used too much of the pre-hardened lobe on the core. The cores are shaped and case hardened to accommodate a number of lobe shapes, lobe lifts and LSAs. If the limits are pushed, there might be quite a bit ground from either the opening or closing flanks and IF the case depth were at the minimum, you could break thru the thin case more easily. The smaller the lobe and the more radical the LSA, either tight or wide, the closer you come to the limits of a given core.

This or improper heat treatment by the core manufacturer is usually the reason for a "soft" cam lobe. Typically a cam manufacturer who buys semifinished cores, as most of them do, would do incoming inspection on the cores for hardness as well as dimensions. The problem with checking case depth accurately is that it is a destructive test; you need to cut up the cam. Just checking the hardness of the unground lobe on the core doesn't give you the whole picture.

The above might not be the root cause, but our manfacturing experience leads me to suspect it may be.

My $.02.

 

I thought that the hardening was done AFTER the lobes were machined. Learn something new every day, I guess.

 

If hardening were after lobe grinding, you'd see a discolored surface with a less smooth surface finish.

On a steel (billet) cam you'll often see the unground surfaces are copper plated. The core is rough machined then copper plated to prevent carburizing in those areas. It is then machined close to final size on the lobes and journals. The distributor gear teeth are probably also cut then.

Next it is carburized, or heated in a carbon-rich furnace atmosphere (at somewhere around 1600F) for a number of hours. The carbon difuses into the surface of the nickel-chrome-moly steel in the areas that are not copper plated. The amount of time in the furnace determines the depth that gets carbon. For steel to harden into the Rc60 range you need for wear resistance, there needs to be at least .60% carbon content. The 8620 alloy normally used is only .20% carbon (that's the "20" in 8620). After carburizing the cam is directly quenched (rapidly cooled) or reheated then quenched to harden the carburized (non-plated) surfaces. It is then tempered at say 400F to remove the brittleness and many of the stresses induced by the quenching. The carburized surface is about Rc60, and the balance somewhere around Rc30-35 or so. The .20% carbon content keeps that "core hardness" down. It is very strong and tough however.

The heat-treated cores may then be straightened, and the journals and nose finish ground. All that's left to do are the lobe surfaces. I believe some cam companies purchase their cores in this condition and just finish grind the lobes. They may also finish grind the journals at the same time IF they use a CNC grinder.

More than you wanted to know...