I reprint things I think have some value to us motorheads.
I did NOT write the following
Since this is quite long, if you'd like to skip all the reading, you can just scroll to the bottom where it says "Summary", to see the windup.
A little while back, I posted the results of my "root cause failure analysis" on BBC solid roller lifters, maybe some of you saw it. For those who didn't see it, and as a reminder for those who have seen it, here is what the failed .842 lifters came out of:
1. 408ci BBC, 243*/249* at .050, .663"/.655" lift, .018/.020 lash, 210/567 lbs spring pressure, Chevron Delo 15W40, Isky Redzone lifters failed at 3,000 nearly all street miles.
2. 540ci BBC, 266*/272* at .050, .678"/.688" lift, .016 lash, 260/650 lbs spring pressure, Redline 20W50, Crower HIPPO's failed at 5,000 nearly all street miles.
3. 632ci BBC, 277*/292* at .050, .848"/.824" lift, .026/.028 lash, 325/875 lbs spring pressure, Mobil 1, Redline, and Royal Purple Racing 20W50, Crower HIPPO's failed after 1 1/2 years. Mileage and driving style not documented.
The windup after careful and thorough examination, was that no matter how mild or radical the cam, how soft or stiff the springs, how they were run, or what oil was used, they all failed for the exact same reason. And that reason was metal surface fatigue failure, which shows up as pitting and flaking called spalling. The axles/needles and in quite a few of the cases, the roller OD's had failed. NOTE: Even the newer Isky EZ-Roll bushing type lifter is still vulnerable to this type of roller OD failure, no matter how good its bushing area may turn out to be in the long run. Improving lifters is a great idea, BUT it only addresses the symptom and not the underlying root problem. And for the record, oiling played no part in these failures at all. They all failed due to fatigue because the load they saw, for their size, resulted in stress psi being so high that their fatigue life was reduced to unacceptable levels, resulting in premature failure. The first step in coming up with a solution, is finding out exactly what is failing and why. With that done, now its time to turn our attention to what we can do to fix, or at least significantly improve this issue, which seems to be becoming a rather large problem, especially with BBC's.
The absolute answer is to reduce the loading, in order to reduce the stress psi the lifters see. If you had a large enough diameter lifter, along with larger needles/axles/rollers/lobes, you could reduce the stress psi low enough, that the fatigue life could be greatly extended to the point where we wouldn't be talking about this anymore. Unfortunately, that isn't really feasible, so where does that leave us with the parts that we actually do have?
Some folks like the idea of Rev-Kits, and they do on the surface do seem like a good idea. Some folks run them and like them fine. But the question is, do they REALLY do us much good? It seems a lot more SBC guys run them than BBC guys, since it is a lot more trouble to try to fit one on a lot of BBC's. I'm not really convinced that they do all that much good in terms of helping roller lifters live longer. Here's why, even though they will keep the solid roller lifter in contact with the lobe, base circle and ramps, you still most likely are running the recommended sloppy loose lash. Well, all that slop didn't just magically go away because the lifter stays in contact with the cam. It still has to be taken out somewhere, and that somewhere is taken out by hammer blows to the pushrod/rocker arm, when the lifter smacks into pushrod, and/or the pushrod smacks into the rocker. And where does all that shock loading get reacted? You guessed it, at the roller/axle/needle interface with the lobe. There is no free lunch.
But even so, do they do us any good or not? Here's one case in point, "Ausbullet" from Australia, ran a modified Crower Rev-Kit on his BBC race boat engine with a set of Isky Redzone needle-type solid roller lifters. And the Redzones failed after about 2 of his race seasons. Hmmm, is that good or bad? He said an older set of non-HIPPO Crower roller lifters, without a Rev-Kit, failed in about half the time. So did the Rev-Kit double the lifter life or not? It's actually impossible to say for sure, because he changed to a different brand of lifter AND changed to running a Rev-Kit. Changing two things at once, eliminates the possibility of knowing for sure what did exactly what. Could be that the Redzones themselves, simply may have lasted twice as long as the old style Crowers. Some have said that they've had reasonably good endurance life out of Redzones before, so it makes it tough to say what is responsible for the improvement. But either way, the Redzones failed in a manner comparable, give or take, to the premature failures we have seen with them in Hotrods and Race cars that were not running a Rev-Kit. So, even though the "Ausbullet" case is only one example, it does seem to point out that Rev-Kits alone, don't really eliminate the lifter failure problem. They may be PART of the answer, but by themselves, they are not going to be enough. More on all that later.
As the old saying goes, "If you keep on doin' what you've always done, you're gonna keep on gettin' what you've always got". Well we just can't keep living with lifters failing so often and risking the whole engine. So, what else can we do? The one place we can still take a look at, is the impact loading that the lifters see at lash point, where all lash is taken up and they actually start moving up their bore and opening the valve. Professional cam designers have said that after the lash is taken out, the loads the roller sees going up the opening side, across the nose and down the back side of the lobe are nothing compared to the hit the roller takes at the opening lash point. And that claim is backed up from what was seen in the failed lifters above. The mild cam's lifters failed way prematurely, just as the bad boy cam's lifters had, even though their acceleration rates up the lobe would be quite different. This all make sense because it is at that lash point where the lifter feels the repeated hammer blow impacts that we hear as a rattle coming from under the valve covers. Of course, repeated hammer blows, is precisely how jack hammers work to break up thick concrete, and repeated hammer blows is how an air wrench removes stuck-on lug nuts. So, it's really a wonder that our solid roller lifters last as long as they do.
Spintron testing has shown that lifters can bounce up and down on the cam's base circle, within their lash slop and even beyond, and can even bounce the valve up and down off its seat as well. In so doing, the lifter isn't always going to be in a position to follow the clearance ramp as intended, but instead it will hit hard somewhere on that ramp. So all the effort the cam designer put into designing that clearance ramp will have no effect at all on how hard the lifter hits, at the point of actual contact. All this brings us to looking at the amount of lash we actually run. The one thing that all the failed lifters above had in common other than that they all failed, is that they all ran the recommended seemingly loose lash. Just for discussion purposes, they average out to about .022 lash (HOT) at the rocker tip where you set lash. But if you consider aluminum headed BBC motors, with the std 1.7 rocker ratio, this still ends up about .013 lash at the lifter. Even though that's quite a bit less than "at the rocker tip", it's still a huge amount of slop for the lifter to bounce around in, and likely NOT follow the clearance ramp as intended. Now consider that hydraulic rollers which pretty much run forever, run zero lash and do follow their ramp as intended. So, they don’t feel repeated hammer blows like the solid rollers do. Hmmmm, maybe we are on to something here. You might say, yeah but they don't run lobes as aggressive as solids do, and they have lighter springs. But that's exactly the point, if milder stuff follows the ramps and lives, it's got to be even MORE important for our more radical solids to follow their ramps, rather than get severely pounded, if they are to have any hope of living. All that constant hammer blow pounding that they currently see, is the smoking gun, as to what is supplying the excessive loading that is reducing the metal's fatigue life and then killing them. Remember that jack hammer, think of the lifters as the concrete that's being destroyed by all those repeated hammer blows from the lobes smacking into them. And the higher the rpm, the higher the impact.
It's almost certain that the first time any of us ever heard a solid lifter motor, that we wondered why it rattled so much. It sure sounded like all that rattling was hurting parts, and it obviously does when it comes to solid rollers. Then if we asked WHY it rattles so much, we'd be told it was because of the loose lash those bad boy cams had to run. Of course that wasn't really an ANSWER, really more of a description as to what's happening under the valve covers. Professional cam designers will tell you that the lifters should follow the clearance ramps that they went to all the trouble to design in, yet the extremely loose lash typically called for, almost guarantees that the lifters won't end up following those ramps as intended, because of their freedom to bounce around. So, maybe some of the Professional cam designers can chime in and really once and for all, explain in detail "WHY" these cams call for such loose lash. Because those same cam designers will often suggest running a Rev-Kit to ensure that the lifters do follow the ramps as intended. Which brings us right back to the question of, "what is the point of all that sloppy lash?", if the whole idea is to precisely follow the ramps. They must have a good reason for all that slop, since they've been doing it that way forever. But engines aside, from a pure mechanism standpoint, you'd want zero lash to perfectly control the motion. If something just doesn't look right, it probably isn't right. And all this sloppy rattling/hammering just doesn't seem right, never has.
So, until the cam designers can provide a detailed and valid reason for absolutely positively having to run sloppy lash (and simply saying that it's because of the ramps involved, isn't an answer, we've heard that already a million times before, so let's have a real answer by giving details and actually EXPLAINING why), let's say we decide to tighten those lash specs some. This is in an effort to increase the fatigue life of our solid roller lifters, by reducing the severity of those repeated hammer blows. And some cam designers have even said that running less lash may help the lifters live longer, which runs counter to that loose lash being called for, and supports the thinking about running tighter lash. The typical engine in this discussion is an aluminum headed BBC, so let's stay with that theme. With this setup, you'll gain about .006 lash from cold to hot, up at the rocker tip. And you have to take into account the rocker ratio as well, because as referenced above, the clearance at the lifter, is different than the clearance at the rocker tip. But of course, no matter what, we have to have enough clearance cold, to ensure that the valves will be seating fully and freely. So, everything in terms of planning our new tighter lash will need to start with sufficient clearance at the lifter, cold. We want to go as tight as we can to help the lifters, but not so tight as to cause the valves any problems. I believe we can accomplish this requirement by running .002 lifter lash, cold. And that ends up equaling .0034 cold, at the rocker tip where we always set lash, with 1.7 ratio rockers. So, set them to a loose .003 and you're good to go. This will endup as .0094 hot lash at the rocker, and .0055 hot lash at the lifter. Now compare that to the averages of the engines listed above, which were .022 hot lash at the rocker and .013 hot lash at the lifter. That ends up being almost a 60% reduction in lifter slop. That has got to provide an enormous reduction in lifter shock loads. How much will that extend lifter life? Its hard to say for sure. That's like asking, if we stop eating pizza, burgers and fries, and instead eat fish, chicken, fruits and veggies, how much longer will we live? Again, it's hard to say for sure, but we know it’s the right thing to do. Same thing for the lifters, it's the right thing to do, to maximize their life. Now that we've minimized the shock loading the solid roller lifters, we still haven't reached the lash free life of the long living hydraulic roller lifters, so what now? We are as close as we can get, by addressing the main problem of the never-ending hammer blow shock loads, but NOW by adding a Rev-Kit, we will have done all we can possibly do, to help the lifters live as long as they can. And only time will tell how much all this buys us. For those of you who just can't accept the idea of tighter lash, just remember, if you keep on doin' what you've always done, you're gonna keep on gettin' what you've always got. Personally, I can't live with what we've always got, so I plan to move forward. Call it crazy or pushing the envelope if you like, but if we didn't do crazy things and push the envelope, we'd still be driving horses and buggies instead of Hotrods and Race cars. Think about it, when guys first started working on horseless carriage (automobile) development and aircraft development way way way back in the day, they were thought to be insane, but look where we are now with that stuff.
There has been some mention of possible performance losses when tightening up lash, due to valve opening/closing changes, duration changes, overlap changes, etc. But you see some of that anyway when you advance or retard a cam. But from the lash changes I've played with myself previously, and from what others have said about their experiences with different lash settings, it suggests that those concerns are more theoretical than real world. As long as you have "some" lash so that the valves can seal and cool normally, you CANNOT physically hurt anything (and you'd better not have your valves so close to the pistons that them hitting could be a concern with such tiny little changes in lift and duration). You can always just put the lash back to normal if you don't like the tighter lash for any reason. You just need to evaluate your combo on the dyno, the track, or even seat-of-the-pants, to see what you think. And you may even find a performance increase. But even if you can't tell any performance difference at all, you'll be in good shape, because you'll be helping your lifters immensely.
FOR MAXIMIZING SOLID ROLLER LIFTER LIFE, I suggest the following when running an aluminum headed BBC with 1.7 rockers:
1. By far the most important - tighten up "cold" lash to a loose .003, which equals a loose .009 "hot" lash. This will keep the rollers very closely following the cam, to minimize the repeated hammer blow shock loads that have been killing the lifters.
2. Optional, but may well be the "icing on the cake" of maximimizing lifter life - install a Rev-Kit, to help deal with the bit of slop that still remains after tightening up the lash.
Beyond these suggestions, we'll just have to "run 'er till she blows". :)
This write-up is bound to generate much debate and many arguments, which always seems to be the case with any thinking "outside the box". But, since I don't see anyone else coming up with improvement ideas that address the root problem, so be it…………….