Are pushrods and springs really needed?

[smokinstroker]

Thanks for the answer guys. This is the stuff that helps educate us younger guys that aren't as knowledgable with internals.

 

[Tree Trimmer]

Thanks for the answer guys. This is the stuff that helps educate us younger guys that aren't as knowledgable you old guys..

fixed it for you.

interesting page there, bft.

i have to admit. i was with lubeowner. his train of thought, made perfect sense to me.

i would never have thought about it like a pole vaulters pole. it takes energy to bend the push rod, and at the end of the stroke of the push rod, the energy would be released, thus driving it higher, past where it would normally stop.

 

[Craig@MFI]

well i tried my hardest to bend a pushrod the last few days and there all still straight but look what failed and what didnt tonight

 

[11STROKER]

well i tried my hardest to bend a pushrod the last few days and there all still straight but look what failed and what didnt tonight

:whs:

 

[Dzchey21]

Exhaust rocker? What kinda back pressure did it take to.do that?

 

[Craig@MFI]

Yes exhaust rocker idk I was driving easy and it went
Everything else was fine lol

 

[Dzchey21]

I'm sure it's been on its way out for awhile. There is a nice stress riser on the square edge of the rocker... plus being stamped doesn't help.

 

[Mike@MPD]

Bp is 1:1

Sent from my Droid Charge

 

[Dzchey21]

Bp is 1:1

Sent from my Droid Charge

So what's that mean 78 psi of back pressure? Is that checking with the factory back pressure sensor?

 

[Craig@MFI]

Pretty near to that hard to watch all guages at once and edge won't datalog

 

[bigrpowr]

yeah without bp info, saying 1:1 is pretty vague. maxing out the factory sensor doesnt say anything. huge back pressure is probaly gonna break a rocker arm, or maybe you can blame that on the h-11's !! LOL

on edit: you think the bp was not crazy high spraying it? that alone coulda caused the fatigue and stress, there's prolly more ready to break.

 

[F250stroker08]

Pretty near to that hard to watch all guages at once and edge won't datalog

If u need a dashdaq to datalog you can borrow mine Craig.

 

[Erikclaw]

This could be the first sign of more to come with the stress that has been inflicted on that motor.

 

[Craig@MFI]

yeah without bp info, saying 1:1 is pretty vague. maxing out the factory sensor doesnt say anything. huge back pressure is probaly gonna break a rocker arm, or maybe you can blame that on the h-11's !! LOL

on edit: you think the bp was not crazy high spraying it? that alone coulda caused the fatigue and stress, there's prolly more ready to break.

I had it wastegated when i sprayed it so i doubt backpressure is very high

 

[lubeowner]

[FONT=Calibri,sans-serif]Just [/FONT][FONT=Calibri,sans-serif]what is valve float?[/FONT]
“Valve float” is a common term for a situation best described as (valve train separation). This occurs due to inertia load imparted into the valve train by the action of the cam lobe against the follower.Weak valve springs are among the most common causes of valve float. Fast lobe profiles, heavy valves, etc force the need for high quality springs with increased pressure. That said, too much pressure can be disastrous to rocker arms and is often unwarranted. Forced induction is another contributor to “valve float”. Because of the increased pressure on the face of the valve, stronger springs are usually warranted.
Flex in the valve train (the majority of which is located in the pushrod) is a prime contributor to valve train separation or “valve float”. The initial loads imparted into the pushrod cause it to bend (somewhat like a pole vaulter’s pole) and then return to a straight configuration. This unloads a sharp energy pulse to the rocker arm, which transfers it into the valve/valve spring assembly. This often results in “valve lofting,” which causes the valve to operate in a different path than that described by the lobe profile. At the same time, the lifter without any load against it, can also be launched off the opening ramp of the lobe and then, as load is re-established, either: strike the nose of the lobe and eventually damage it; land on the closing ramp (like a ski jumper landing on the slope of a hill); or land on the base circle with significant and often damaging impact. If “lofting” can be controlled (by design or good fortune and the lifter lands gently on the closing ramp), it adds to area under the curve and more power. If it is uncontrolled (which happens the vast majority of the time), it can be damaging to valve train components and will compromise performance. Most of the time, power flattens out or is lost when valve train separation occurs. Again, the biggest culprit in causing this situation is the flex of the pushrod.
Many people on website forums tend to think that the “weight” of the rocker arm is the cause of “valve float”. If the rocker is rigid and properly designed, it should contribute very little to “valve float”. Weight in this case is not the prime issue, but rather the “moment of inertia” of the rocker design. “Moment of inertia” is the affect of where the mass of the rocker arm is located relative to its center of rotation. One rocker can be much heavier than another and still have a smaller moment of inertia because of where its mass is located; so weighing rockers to determine their affect of valve float is really not effective at all. (FYI: “mass” is a measure of a body’s inertia; while “weight” is the affect of gravity on “mass.” “Moment of inertia” is unaffected by weight, but is affected by where “mass” is located relative to the center of rotation!). The highest quality aftermarket rocker arms are designed to be rigid (to minimize flex), and have a very low moment of inertia relative to the necessary strength.

Other issues are often misdiagnosed as “valve float”. These issues can mask themselves and give the impression of “valve float”.
11 1. Coil Bind.
Increased lift causes the clearance between the valve spring coils to diminish. The spring can become solid. The minimum recommended clearance is .060”.2.Additional lift can cause the pushrod to travel a different arc. The position of the pushrod in the rocker arm cup and or additional lift can reduce the clearance between the pushrod and the cylinder head. If the pushrod contacts the head during its rotation, it can stall momentarily causing the lifter to expand and pump up, holding the valve open temporarily. The result manifests itself exactly like “valve float”.
3. Proper rocker arm clearance, that is, something interfering with the ability of the rocker to make its full sweep can manifest itself as “valve float”. Clearance should be checked throughout the entire sweep of the rocker arm. The minimum recommended clearance is .60”
Understanding the issues surrounding the phenomenon of valve train separation is paramount in identifying the problem and correcting it. To ensure consistent performance and safety throughout the entire range the engine operates in, valve float must be controlled. Unchecked, valve float can and usually does, contribute to engine destruction.

I enjoy the educational reading. This has shown me there is a point that I had not considered, and that is the pole vaulting effects of the push rod, I am going to have a few conversations with a couple engine builders I know to see what they know of this. Maybe something I should have been considering all along and just over looking.

What I do understand is floating a valve and the damage that can cause. Anytime you have clearance in the valve train is will cause a slapping effect on the parts like the rocker arm and push rod. Thus most much of the time valve float ending in a bend push rod or broken rocker arm. I just haven't ever thought of the push rod being part of causing float. What I had considered is cam profiles, weak springs, rpms and backpressure.

It is all know that forced induction is way harder on the valve then naturally aspirated. This is due to the boost and back pressure forces on the engine. Boost pushing an intake valve open and back pressure pushing the exhaust valve open. I still 100% to this day, even with considering the push rod effect, believe that valves touching the pistons is because of high back pressure holding the valve open. Then the bent push rod or rocker arm comes from the valve being held open and have valve float going on. Maybe this rod flex is the cause of it?

 

[switchmode]

This is always something that surprised me that we upgrade all our valvetrain but nobody has taken the time to upgrade the rocker assembly. I know when I helped Shane disassembly his new engine to goto the machine shop there is really not much material to these rockers and a square hole is one big stress riser at every corner even if there was a small radius in each corner the stock unit would be alot stronger for the breakage that occurred in Craig's case. I know everyone's arguement would be these are extreme conditions but everyone has the possible of seeing these kind of fractures due too the design just not as fast a Craig because the more power your making exponential decrease lifespan.