Found this interesting.
In order to explain everything involved with this complex issue, the write-up is extremely long. However, those keenly interested in this problem, may want to take a look anyway. Perhaps printing it out, then reading parts of it as you get a chance, might be the way to go.
I believe I have found the root cause for solid roller lifters failing prematurely in street motors. Hopefully others can benefit from this information as well, so I wanted to share my findings with like minded professionals and enthusiasts. To do that, I've sent this out to various Hotrod type magzines and web Forums. This is what I found with my particular combo, but of course your results may vary. Though I have to expect that this is likely a common issue among all engines with the same type of lifter oiling design.
I'm in the process of personally building an all aftermarket 540ci BBC. I'm using a Dart Big M std deck block, along with a Comp Cams billet solid roller cam, Crower Severe Duty solid roller lifters (using 17 needles, each with .071 diameter) with HIPPO, and Crower stainless full roller rockerarms. The cam is 266*/272* @.050, with .700" actual measured valve lift with .016 lash. Valve spring pressure is 280 lbs on the seat, and 700 lbs on the nose. I'm going through the entire engine very carefully and blueprinting everything. In the process, I made a startling discovery, which could be easy to miss. I found it when I looked through the oil passage at the front of the block, with all the pipe plugs out. The Dart block oils the lifters from the front of the block. At max lift, the 7/16 or .4375 diameter oil passage that runs through the entire lifter bank, is within .080" of being entirely shut off by the lower edge of the lifter oil band, nearly stopping the oil flow through and to the lifters down the line. In addition to mechanically blocking oil flow, you have the flowing oil dynamic issue, of the likelyhood of reverse pressure spikes as the oil passage is effectively slammed shut. This is similar to a large ocean wave slamming into a concrete sea wall, and spashing back the other way. The size of the block passage itself isn't all that important as long as it's big enough. What is important is the amount of opening that remains during the up and down motion of the oil band on the lifter. More on that below.
When I talk about lifter oil flow, I'm talking about having at least enough flow IN, to keep up with the bleedoff flowing OUT. That is the minimum flow required to maintain oil pressure. Any less flow IN, than that minimum, results in a loss of oil pressure. With insufficient flow/pressure, roller lifters have to get by with only bottom end oil splash, residual oil present and any spurting, sputtering or gurgling oil that does make it in through the passage. Roller lifters don't have the benefit of any oil wedge action holding needles and rollers apart, like bottom ends have with their concentric design and uniform clearance. So the only thing between premature lifter wear/failure, or lasting as long as we'd like, is a steady flow of pressurized oil to both lubricate and cool. We've seen noticeable improvement with pressure fed needles over the earlier type that didn't have that. This supports just how important enough oil is, though even the pressure fed needle type still don't last as long as we'd like. The load on the needles is high as lifter upward acceleration begins, and at max lift, that 700 lbs "on the nose" spring set, will put about 1200 lbs on the lifter needles, due to the rockerarm ratio involved. With my particular lifters, only 3 of those little needles are carrying that 1200 lb load at the point of contact. The lifter needles all spin the same direction of course, but since they are not caged like a wheel bearing, their side surfaces not only press against each other, but as one surface is going up, the other is going down. Without enough oil, it's easy to see how wear and/or outright galling can occur, which spells the beginning of the end of the lifter.
Some Pontiac and Chevy LS engines feed the lifters individually from the side of the lifter bores rather than in-line through all the bores in a bank. With the "individually from the side" oiling design, individual lifter position doesn't affect oil flow to the others, so there is no issue with those engines. Dart stayed with the old BBC stock "in-line through all lifters" oiling design. This old "in-line oiling" design means that the oil flow to a particular lifter in that bank, is affected by the lifters in front of it……..not good!! If you wonder why Chevy would design something that bad, the answer is, for their needs, they didn't. If I had only around .550" valve lift or less, I would have NO OIL RESTRICTION AT ALL, NONE!! So, for stock or mildly modified engines, there is no oiling problem with the in-line lifter oiling, they won't see our lifter failure issue. Only big lift, street engines have the oiling issue. Race motors are typically watched much closer, and any issues with lifters will usually be caught before anything is damaged beyond the lifter itself.
When I first came across this "blocking the oil flow" issue during my build, I thought, how could this be, wouldn't all this be figured out by now? But then, almost shutting off oil flow at max lift is just a momentary thing, right? So maybe it's not that big a deal……or is it? Not being one to just assume things are OK, I decided to look into it further in order to really know for sure. This whole pursuit became very involved and tedious, was extremely time consuming and the measurements were somewhat difficult to do with an acceptable degree of accuracy. On top of that, due to the nature of the oil passage/lifter interface being curve on curve, the math was difficult enough that hand calculations were out, so I modeled the interfaces on the computer, and had it calculate the orifice areas at many different positions. The analysis ended up being so involved that it is likely beyond what the typical professional or enthusiast would care to pursue. More below on simpler suggestions.
I started out by considering the orifice area in square inches, that was needed at the front of a bank, to support the bleedoff of the 8 lifters behind it, vs what I actually had. Then the next lifter interface in, and the bleedoff of the 7 lifters behind it, etc, etc, until I had accounted for the whole lifter bank. I also accounted for the oil restricted zone overlaps due to firing order, so as to not add them in seperately, which would skew the results. The bleedoff I'm referring to, is of course from lifter to bore clearance, the needle bearing feed passage diameter, leakage at the end of the pushrod from lash, and the oil squirting out of the rocker arm up top. In my paticular case, the rocker arms are counterbored at the pushrod socket, so oil never stops flowing out of them, no matter what the angle is between the pushrod and rocker. Good for oiling valve springs and rockers, but not so good in terms of bleedoff. Then I determined how much the lifters would have to move down to enlarge the orifice area, in order to flow enough oil to support all the bleedoff, and the crank angle involved with that. My lifter to lifter bore clearance is .0015", more clearance would put you in worse shape due to even more bleedoff. I have one .024" needle feed hole in each lifter, more holes would put you in worse shape, again because of additional bleedoff. And I have .700" valve lift as mentioned above, more lift would put you in worse shape, because of closing off the passage even more of the time. Its all about the amount bleeding off vs the amount that can feed in. Ultimately I came up with individual crankshaft degree ranges where the oil flow restrictions could not support the bleedoff taking place. Then I added up all those seperate ranges for a total number of crankshaft degrees where I had the problem.
In the end, I found that I didn't have enough open oil passage to support all the lifters in the bank, about 360* out of 720* for a complete cycle. In other words, I had a serious oil flow restriction happening about a whopping 50% of the time. That result prompted me to double check all my analysis, to make sure that number was in fact correct, which took even more time. The results were correct, so things checked out to be far worse than what that first glance might have suggested. This situation does not meet any engineering requirement, not even stock, not by a long shot. You'd expect these lifters to fail, and be surprised if they didn't. It's not a matter of "will they fail", but rather a matter of "WHEN will they fail". We've wondered WHY these things don't last long enough, and that oil restriction is the answer, at least on my combo. And it's undoubtedly the answer on other combo's as well. The problem is so obvious with my engine, that it doesn't take an advanced degree in Mechanical Engineering to see it. Considering the adverse conditions these lifters operate in, it's amazing they last as long as they do. If they failed because of inferior material, we would expect failures to be more a specific manufacturer issue, and a more uniform failure across a whole engine, but we don't see that. In fact, we see failures from every brand of roller lifter out there, no matter who makes them or what they cost. In addition to that, restricted oil to the lifters means restricted oil up top. So, while this oil restriction problem is in the process of deteriorating the lifters, it's also reducing the life of the valve springs because of the reduced oil flow over them, which they depend on for cooling. So, it's a double whammy situation.
It's a situation of fix it now, or fix it later, but I WILL have to fix it. If I don't do anything to improve the problem, it is like playing Russian Roulette with my engine. The sensible thing is to fix it now, while I'm in the process of building the engine in the first place. So, with the block back from the machine shop, and already cleaned, the question is, what is the most workable way to proceed? The best way to fix the problem with the block I have, would be to do some plumbing in the lifter valley. Joining all the lifter bores together with a common oil pipe, would do the trick. But that brings with it, a certain amount of complexity, and potential for leakage and/or breakage while in use. Using a somewhat simpler method of plumbing, and simply tying both ends of lifter bank together would also do the job fairly well, but brings with it the same concerns. I prefer the KISS principle, so I decided to modify the oil band (the center area of the lifter that is smaller diameter) on the lifters themselves, which is much simpler.
To modify the lifter's oil bands, I ground a .100" chamfer on the lower edge, front AND back, at the interface of the lifter and oil passage. And also a .150" chamfer on the upper edge, front AND back, also at the interface of the lifter and oil passage. The lower chamfer still leaves about .200" overlap between the lifter body and block, at the lowest position of the lifter. This maintains lifter support in the bore as well as oil pressure. If the chamfer were too low, you'd be down below the edge of the lifter bore, and you'd not only lose lifter support in the bore, but you'd be blowing out oil and losing oil pressure, which would defeat what you are trying to do in the first place.
After the mods, I ran the complete analysis again to see how much I had been able to improve the oiling situation. The results now showed that my oil restriction occurs about 150* out of 720* for a complete cycle, or about 20% of the time. That was the best I could do with lifter mods alone. Still not ideal of course, but going from inadequate oiling 50% of the time, to only 20% of the time, is a HUGE improvement. In addition to that, the chamfers on the lifters smooth the oil flow into and out of the individual lifter bores, by tapering open and tapering closed. In so doing, they reduce the likelihood of those reverse pressure spikes mentioned above, which can occur when the original lifter oil band edges almost instantly slam off the oil flow. When you factor in that additional improvement, then the modification is likely even BETTER than what the 20% vs 50% might suggest.
So, I'm confident that with the big improvement the lifter modification made, when combined with two other aspects that I feel are critical, the lifters will finally have the reliability we've been looking for. I believe the two other critical aspects are:
1. ELIMINATION OF THE OIL FILTER BYPASS -
Because even minor damage to a roller needle can ultimately result in failure of the lifter, it is critical to prevent any debris, no matter how small, from ever getting to that needle area. In order to do that, you need to ensure that the oil filter is never allowed to bypass. Oil filter bypass valves, whether in the block or in the filter itself, are actually quite simple in concept. They open when there is typically around 9.5-10 (but that can vary, depending on the particular filter) psi delta across them. In other words, if a condition exists where temps, viscosity, oil flow from the pump, and oil filter restriction are combined such that the filter entry side see's, say for example 40 psi, but the filter exit side see's 30 psi or less, the valve opens and now you are pumping unfiltered oil. Any number of scenarios can bring that about. Of course the first thing that comes to mind is cold oil on start-up, but enough rpm (which increases the pressure against the filter, at least up to relief valve pressure) for the viscosity being used, combined with a restrictive enough filter (one of those fine 10-15 micron types for ex), and it's easy to see how you can bypass even at normal operating temperature. It's a scary thing, to think about how much bypassing is actually going on, because you can't see it on the oil pressure gauge.
To avoid all that, I'm using an oil filter bypass eliminator adapter, a Moroso 2qt high flow (moderate restriction) Racing oil filter which has no bypass in it (many oil filters do, even though they aren't advertised as having one, you have to carefully check to be sure), so as to avoid any significant pressue drop through the filter, and one or two Filtermags. This set-up will flow plenty of always filtered oil, while filtering out even the smallest particles.
2. USE A NON-CAVITATING OIL PUMP -
By design, conventional stock type spur gear oil pumps, will cavitate at certain rpms, whether stock or modified. At high rpm, the twelve individual spur gear teeth are simply opening and closing too quickly to completely fill the small segments between the teeth, creating gas bubbles that result in cavitation. Spur gear pumps have over seven times as many pumping pulses as a gerotor oil pump, at any given rpm. When a spur gear pump cavitates, the LIQUID oil being pumped can drop by as much as 70 or 80%, leaving it pumping mostly FOAMY oil, which is the last thing we need for our lifters that already have inadequate oiling. On top of that, shock waves from the cavitation, is what causes pickup tubes to break and housings to crack.
The solution here is to simply use a gerotor oil pump. By design, it's larger, slower, smoother "bites" of liquid prevent bubbles from forming, so it can never cavitate. This means the gerotor oil pump will pump liquid oil 100% of the time, and this all liquid flow will obviously benefit the rest of the engine as well. It's been my experience that gerotor pumps generate significantly more oil pressure at idle and at lower rpm than what spur gear pumps can muster, which is another big plus for our lifters. This is perhaps the final piece of the puzzle to increasing the life of our solid roller lifters. I'm using a Titan Sportsman gerotor oil pump, which is more expensive than a conventional pump, but I think it's cheap insurance for an expensive engine.
SIMPLE SUGGESTIONS FOR CHECKING YOUR OWN ENGINE:
Based on what I found with my engine, I can offer some simple suggestions for checking your own engine. This simplified method won't be as precise as doing the full exhaustive and time consuming analysis I went through, but it can get you close enough to decide if you should consider doing modifications. The single most important thing is to check how much lifter oil passage is still open at full lift. You'll of course need to have at least one lifter out of it's bore to do this. With a lifter out, roll the engine over until that lobe is at full lift in that bore. Now you want to measure the distance from the top of the lobe to the top of the block's oil passage that goes through the whole lifter bank. Using a scale and a flashlight will come to mind, but due to parallax error, you won't get accurate enough numbers to rely on. What works quite well, is to use a notepad's cardboard backing and cut out a simple measurement gauge with scissors, until it exactly touches the TOP of the oil passage while sitting on the nose of the cam. You may have to trim it a few times or even make a second one to get it right, but it isn't that difficult to do. Once done, simply measure it with a dial caliper and you have your distance. Then set your lifter on a flat surface and measure it from the bottom of the roller, up to the LOWER edge of the oil band on the lifter. If the lifter measurement is less than the lobe to passage top measurement, then you have some oil passage open at full lift. If you have bleedoff clearances fairly close to mine listed above, and if you have about .225" or more open at the top of the passage, then you should have no oil restriction and you're good to go as is. If you have less than that open at the top of the passage, if you have larger bleedoff clearances or more needle feed passages than I do, then you might want to consider making some modifications to improve oil flow in your own engine.
Hopefully this write-up has been helpful in giving others something to consider with their own builds. And maybe we can put solid roller lifter failures behind us once and for all.