BBC solid roller lifter failures - a root cause analysis

[judgement_impared]

Man, who has a spintron and a high speed camera that we can test these theories with??

Come on, one of you guys MUST have one sitting around gathering dust that we can do some testing with..

I too would LOVE to see the differences (if any) a rev kit would have. I would think a camera angle showing the roller/cam contact would be beneficial as well.

[TheEngineWorks.com]

Throwing this at my guy at Comp Cams, he feels that the lash accually ADDS in roller lifter abuse, he said some of the sprint car guys run just about zero lash cold and the lash grows to around .012/.014..

I am gonna go with the same cam and lifters, but I am gonna run about .002 lash cold.. We will see if that helps some.

[panic]

"Maybe the lack of pressure allows the roller to stop rolling, and then when it hits the lash point, the sudden acceleration of the wheel is too much for the needle bearings, and the skid inside the wheel."

I think that's it. Oil viscosity etc. inside the roller assembly slows rotation whenever there's lash, and then the roller must accel to speed instantly when the lash is taken up and the needles skid, the roller OD skips on the lobe etc. Can't be good.

Just a guess: the older rev kits were designed for use with mild rocker ratios (1.5-1.75?), and if you're higher than this remember that you have more spring load on the tappet already due to ratio, so the rev kit spring load should be relaxed somewhat.
This means backing off the main spring stack somewhat?
That would be nice, because it also takes load off the pushrods!!

[af2]

I too would LOVE to see the differences (if any) a rev kit would have. I would think a camera angle showing the roller/cam contact would be beneficial as well.

The only advantage I can give is when rocker studs broke and left the roller lifters in place and not pitching them. As far as power. No. As far as helping with a breakage. Yes.

[MadBill]

If used for the sole purpose of maintaining roller contact, a rev kit could probably use much less spring pressure than usual, since this seems to be predominantly a low speed issue..

[Unkl Ian]

Is this a "new" problem, related to the newer oil formulas,
or are people trying to run the most radical available cams, on the street ?

[TheEngineWorks.com]

Is this a "new" problem, related to the newer oil formulas, or are people trying to run the most radical available cams, on the street ?

BOTH!

I think the oils today w/o real good ZDDP packages coupled with the radical profiles are combined a recipe for disaster, BUT that does not mean by working together we won't find a happy medium to the problem.

I think this is a start right here. Being in the forefront of trying to figure out how to have the best of both Worlds, I hope we continue the discussion here and elsewhere..

We have made OVER 1100HP on 93 octane on a regularly "street" driven car, we did have roller issues, but I feel those problems started w/ overheating issues, of which we already have figured out, BUT I feel we realized some other things that can be an issue with accelerated valve train wear, one of which being, the lash issue CAUSING some of the wear of the rollers, I am working on how to deal w/ those issues right now.

[BLACK BART]

Regarding the use of a rev kit or not I pose these questions:

If the lifter is in a free floating position when there is lash in the system how can this be a good thing for the needle bearings when they are pounded by the cam lobes as that lash is taken up? We don't hit our differential axle bearings with a hammer and expect them to live do we?

What happens to the running lash between the lifter/push rod, push rod/rocker, and rocker/valve when you take up the lash between the lifter and cam? It opens up.

What happens to the parts mentioned above as a result of the increased running lash? They take a greater pounding than before.

What if a rev kit was run along with a tighter lash? I would think you could see a much more durable combination for a given lobe intensity or valve train combination.

I believe Mr. Jones and Mr. Miller are on the right track. When you try to do more with less, it's my experience that the little things are just that much more important. CJ

[Unkl Ian]

Now that I think about it,the OEM rollers are all hydraulic.
So they don't experience lash clearance.

[Strange Magic]

Who actually made the decision to incorporate an average of .024-.028 for a mechanical roller camshaft? Who actually made the decision to incorporate .020-.024 for mechanical tappet camshafts? Who actually made it industry standard to recommend that the majority of camshafts be installed with the intake centerline 4 degrees advance?

None of the above has to be and there is no accurate data that proves this to be benificial.

[xenginebuilder]

Who actually made the decision to incorporate an average of .024-.028 for a mechanical roller camshaft?

Well, a lot of high performance and even current OE cam design uses long constant velocity clearance ramps, and have done so from the '30's.
Both Mike Jones and Harold Brookshire have devoted many posts to the subject of lash.
In the context of roller loading and failure, the important factor is not the lash, but what velocity is encountered at the lash point. The distance does not matter if the velocity is low. If however, the cam designer picked a "safe" clearance point say at .020", and the lash is opened up to .026", the collision speed is increased dramatically and loading goes way up.

None of the above has to be and there is no accurate data that proves this to be benificial.

I would say that you have to define the engine use and material to make a decision on lash ramp. An all iron small block will not change lash more than a few thou either way, an all aluminum tall deck block with alum heads can change .018" just getting to temperature, let alone another 50 to 60 deg as experienced by TheEngineWorks.com. In that particular application, a long clearance ramp would be very desirable, whereas if he was confined to track only, a tighter, more aggressive clearance ramp could be deployed.

When this discussion started, I pulled out some old "good used" roller lifters that I had kept around for spares, and pressing out the center pins I observed the surface fatigue that 540 RAT was talking about. I have never tried to look at this before. The needle rollers still look good, and the inner and outer surfaces of the roller still look serviceable, but the support pin has eroded clearly around the bottom third of the pin and eventually would lead to a failure. So much for "good used", NOT.

Edited

[PWMAX]

I personaly think the key to lifter life on the street, for sure is a rev kit. I have many guys running on the street with rev kits, and not one lifter issue. I did have one guy, spit 2 lifters, at different times, that didn;t run a rev kit. He didn;t want one in the beggining, because his buddy read on the internet, that they were old school. I said, what is the negative to it? He couldn;t answer that, but didn;t want it because his buddy, who, after all, has a mid 11 second big block car, with a 150hp nos kit, so, he MUST be an expert, and plus, he didn;t want to spend the $140 on one. After the second lifter went, I insisted it got a rev kit. He agreed. The 2 lifters were 1 in the 1st summer, and the second the 2nd summer. After the rev kit, he has now 6 summers on the same set. He drives this car 3000+ miles a summer, and makes probably 80 passes a year. Same brand of lifters, not 1 problem since. Was it the rev kit that made the difference, I personaly think so. They should actualy re-name it. And call it a lifter saving kit. Thats the only thing it really does. It keeps the lifter on the cam at all times. Think about it, otherwise, the lifter can jump, and slam back into the cam, and it get hammered. My advice, if the lifter you use will accept a rev-kit, not all do, I would use one

Frank

[TheEngineWorks.com]

I am happy to hear that some of my original thoughts about the most likely cause of roller lifter failure on the street would be the roller always slaming into the lobe taking the lash out..

What got me started down this path is the telltale signs on some cams of the impession on the cam at the start of the lobe, right where the lash would come out, it stands to reason that if it is making a clear impression on the cam, it MUST be impacting the lifter pretty hard, kinda like pounding a hammer to it, which bearings roll great, they just don't like that crushing impact...

I don't know if its at all possible for me to fit a rev kit on my KB block.. It will take some serious machining.. I may just have to go with the .002 cold lash, or maybe set lash hot and let it run like shit until it gets some heat in it.

[CamKing]

it MUST be impacting the lifter pretty hard, kinda like pounding a hammer to it, which bearings roll great, they just don't like that crushing impact...

That's why the velocity at the opening lash point on my cams is about 1/2 of what you see on other cams.

[MadBill]

..I may just have to go with the .002 cold lash, or maybe set lash hot and let it run like shit until it gets some heat in it.

Minimal lash sounds like a good plan, but what is minimal? The famous 30-30 (thous) Duntov cam came into existence when Corvette Chief Engineer Zora Arkus-Duntov found that the cause of burned exhaust valves in racing (all iron) SBCs of the era was the then specified ~0.010" cold exhaust lash going negative at full operating temperature, due to expansion of the 1400°F. exhaust valve...