Long Tale of Woe
A few years back I decided to rebuild the 440 in my GTX. I was getting some blow-by, and wanted a little more horsepower than that from the factory. I sent it to my local machine shop and had it rebuilt. I purchased a new COMP cam with lifters and springs to match. Break-in oil and lube was installed, and the cam was broken in to COMP's specs. It sounded great and ran great—for as long as it held together.
I got about 500 miles on the engine, and it developed a knock/bad tap. Upon removal of the intake, I found that it had eaten a couple lobes off the cam. I bought another COMP cam, and installed it. This time I didn't even get it out of my garage before it ate that cam as well. I next installed a Mopar cam with new lifters and springs after cleaning the engine. This one lasted about 2,500-3,000 miles before it ate another lobe.
During this ordeal (please understand I was using Brad Penn Break-In oil as well as ZDDP additives), I had spring pressures tested, spring heights, push rod lengths, so on and so forth. So I ordered another Purple shaft with new springs, and left the inner spring out when reassembling the engine. It ate the fourth camshaft after about 1,500 miles. I can't tell you which lobes and lifters were eaten on the first two, but, I think it was the Number 6 exhaust each time.
After the failure of the third cam, I ordered a set of roller rockers as well as a set of Rhodes variable-duration lifters for the fourth cam. I put the roller rockers in, but didn't install the Rhodes lifters; I don't know why. After this last cam, I was looking at the Rhodes lifters, and noticed a vast difference between the Rhodes and the previous two sets (I kept all cams and lifters). The oil groove on the old lifters is approximately 5/16 inch from the top of the lifter, and approximately 1/8-inch wide. The groove on the Rhodes lifters does not start until 3/8 inch from the top, and is approximately 3/8-inch wide. They also have a small groove that runs vertically on the lifter.
I looked in the lifter bore and what I saw this time was the thickness of the block from the top of the oil galley to the top of the lifter bore. This distance is 3/8 inch approximately. This means that the lifter oil-groove is never getting into the oil galley (or only for a very short duration). Could this cause the failure of the cam? I feel it is an oiling problem because the rest of the lifters have wear on the sides as well as the face of the lifter and the cam lobes. The engine appears to have plenty of oil in the galleys. I can find no difference in the fit or clearance with the lifters, but Number 6 exhaust is the one that has failed the last two times. I'm fairly sure it was the one that failed the first two times. I have put in a stock oil pump twice; do you think I need to go to a high volume pump?
Wow, Jim, four cam failures in a row? You seemed to be upset at a particular cam company at the beginning of the letter, but even after using another cam brand you had two failures. I think after four cams, we can reasonably rule out defective camshafts. Next, the lifters most commonly sold these days, the HT-2011s, are different in the body compared to OEM and some aftermarket units like the Rhodes set you described. The oil band is to supply the lifter's internal mechanism with oil, and if the lifters are pumping up to zero out the lash, they are getting adequate oil. Countless engines have been assembled with this style of lifter without problems. Unless your failed lifters did not fill with oil, and you would hear the tappet clatter, I think we can count out the lifters. As far as the high volume versus standard oil pump, the standard pump should be plenty, as long as it provides normal oil pressure. Lube is certainly a concern, but you seem to be using good oil and ZDDP, so that's not it.
Were the lifter bores lightly honed after the block was cleaned? If the engine was cleaned by baking and shot tumbling, the tops of the lifter bores often peen over, creating a tight spot. Flat tappets need to rotate in the bore, and if they do not, they will fail. This rotation should be confirmed during assembly. Next, we have the lubrication. The cam gets most of its lube from oil bleeding down the sides of the lifter bores, and from oil slung up from the crankshaft. This is adequate as long as the lifter clearance is at the required spec, and here is another potential problem. The factory calls for .001-.0018 clearance between the lifter and bore. Too tight and it will bind and fail to rotate, and restrict oil flow. Usually this is from a tight spot or burr at the top or bottom of the bores. On the other hand, the bores may be too loose, and not properly supporting the lifter. An extreme possibility on the clearance issue is an oversized tappet bore. Oversize tappet bores and corresponding oversized tappets were used both at the factory and in service. In this case putting in a standard-sized lifter will be serious trouble. Bottom line—check the lifter to bore clearance.
Now that covers the cam and lifter points, which leaves the valvetrain considerations. First, as the spring loads increase, reliability decreases. You didn't indicate the spring loads that were run, but for a mild street hydraulic 125-130 pounds on the seat, and 300-320 pounds open should be plenty. You need to actually measure the installed height and the actual open and closed load, ensure coil bind clearance, and ensure retainer-to-guide clearance at full lift. A mistake in the spring setup can cause cam failure. When setting up the valvetrain, make sure there is clearance between the rocker body and retainer, and that the preload is set to specifications, .020 to .030 inch will work well. If all this checks out, the only thing left is lifter bore geometry. Variations in factory blocks can create a misalignment between the cam and lifters, and this presents a problem with a more aggressive aftermarket profile. To fix a problem here, the lifter bores will need to be corrected and bushed. An alternative that might be attractive at this point is a retrofit hydraulic roller cam and lifter package.