Issue with Stamped Steel Rockers in BB Chevy

[Chris Hill]

Just curious, but what is the issue with BB Chevy rockerarm? I did not want to hi-jack the excellent thread elseware in the tech forum.

We've had good sucess with the standard small block chevy rocker arm set-up up to and around 7,200 to 7,400 rpm with our V-6. It is identical to the standard small block chevy set-up with a 1.94" intake valve. The only issue we've had was one of the OEM rocker studs that was pinned broke when we first built it in the mid 90's. We then installed the ARP studs and have not had any issues since (knock on wood).

[SSDiv6]

Originally Posted by Chris Hill

Just curious, but what is the issue with BB Chevy rockerarm? I did not want to hi-jack the excellent thread elseware in the tech forum.

We've had good sucess with the standard small block chevy rocker arm set-up up to and around 7,200 to 7,400 rpm with our V-6. It is identical to the standard small block chevy set-up with a 1.94" intake valve. The only issue we've had was one of the OEM rocker studs that was pinned broke when we first built it in the mid 90's. We then installed the ARP studs and have not had any issues since (knock on wood).

The issues are various: fulcrum area wear, rocker arm stud breakage, piercing of the rocker arm push rod cup.

Chris, how much spring pressure are you runing?

Time to chime in!

Well, I bet we run the lowest spring pessure. 149lbs. closed.

Any takers?

Big blocks with .520 lift though.

Jason

[Chris Hill]

In my previous professional life, generally when you had a valvetrain failure, the failure was caused by an impact somewhere in the valvetrain. The impact occurred when unwanted lash occurred in the valvetrain.

The major causes of lash comes from too little valvespring force either from too small valve spring load or a valve spring harmonic issue that causes too small valve spring load (beehive springs help with this). Also, the valvetrain can have another issue with the entire system (not including valve spring stiffness) stiffness and mass and it can be excited into a harmonic issue. To say controlling a valvetrain effectively is difficult is a gross underestimate, especially at the high rpm necessary to make good power.

You say the major wear items are fulcrum area wear, rocker arm stud breakage, piercing of the rocker arm push rod cup. I would believe that when you have lash and impact, the force on each of these areas would increase exponentially and overstress and fail the rockerarm or stud if this happens repeatedly.

The rocker arm failing may be the reliability issue racers have experienced. But more than likely, the proper solution is to have a properly designed valvetrain system that will eliminate unwanted valvetrain lash during engine operation. We have used Chris Padgent at Lunati then Comp Cams for our camshafts for almost 20 years and have good reliability and we’ve always been pretty competitive in the classes we’ve run.

On the last v-6 I put together, I think I had 125 or 135 lbs of force on the seat, nothing very high. This was with a standard lifter face. Dad’s v-6 he built that was stupid fast has Schubeck lifters and around 180 to 200 lbs on the seat. Unfortunately, I can’t remember any of the peak lift force numbers.

SSDiv6, thanks for the points you have presented in the other thread. I have enjoyed reading them.

Thanks,

Chris,

Because I Know you and I am at a bar in KC, I'd RATHER CUT TO THE CHASE.

ARE WE TALKING ABOUT HOLLOW VALVES OR REGULAR NOT HOLLOWED VALVES?

IN STOCK OF COURSE?

[Jeff Lee]

Originally Posted by Jason Fuller

Chris,

Because I Know you and I am at a bar in KC, I'd RATHER CUT TO THE CHASE.

ARE WE TALKING ABOUT HOLLOW VALVES OR REGULAR NOT HOLLOWED VALVES?

IN STOCK OF COURSE?

Well I wasn't going to go there but I was just about to mention valve weight does (or should) have an impact on rocker arm life, especially with high RPM. Chris mentioned beehive springs and I would think that would have another positive impact due to the reduced size of the retainer and I assume, the keepers. Which did make me wonder why beehive springs were legal in the first place as historically the NHRA rule book specifically prohibited the useage of non-steel, non-stock diameter retainers. I believe that stipulation was in affect through 2005?
And speaking of harmonics, I know of a few stocker racers that attributed the breakage to the use of a two step. They seem to be in the minority from what I can tell.
FYI, I too have used Chis Padgett extensively at both Lunati and Comp Cams.

[SSDiv6]

Originally Posted by Chris Hill

In my previous professional life, generally when you had a valvetrain failure, the failure was caused by an impact somewhere in the valvetrain. The impact occurred when unwanted lash occurred in the valvetrain.

The major causes of lash comes from too little valvespring force either from too small valve spring load or a valve spring harmonic issue that causes too small valve spring load (beehive springs help with this). Also, the valvetrain can have another issue with the entire system (not including valve spring stiffness) stiffness and mass and it can be excited into a harmonic issue. To say controlling a valvetrain effectively is difficult is a gross underestimate, especially at the high rpm necessary to make good power.

You say the major wear items are fulcrum area wear, rocker arm stud breakage, piercing of the rocker arm push rod cup. I would believe that when you have lash and impact, the force on each of these areas would increase exponentially and overstress and fail the rockerarm or stud if this happens repeatedly.

The rocker arm failing may be the reliability issue racers have experienced. But more than likely, the proper solution is to have a properly designed valvetrain system that will eliminate unwanted valvetrain lash during engine operation. We have used Chris Padgent at Lunati then Comp Cams for our camshafts for almost 20 years and have good reliability and we’ve always been pretty competitive in the classes we’ve run.

On the last v-6 I put together, I think I had 125 or 135 lbs of force on the seat, nothing very high. This was with a standard lifter face. Dad’s v-6 he built that was stupid fast has Schubeck lifters and around 180 to 200 lbs on the seat. Unfortunately, I can’t remember any of the peak lift force numbers.

SSDiv6, thanks for the points you have presented in the other thread. I have enjoyed reading them.

Thanks,

Chris, there are so many parameters to take in consideration when it comes to valvetrain harmonics, that I could write a book. Another factor that needs to be considered is the valve train geometry: some makes of engines have a geometry problem that will exuberate the problem. Examples of engines with geometry issues are small block Mopars, Oldsmobile and Buick. One problem is that many cam manufacturers design their camshafts based on the acceleration, velocity and jerk at the valve and lifter, They do not take in to consideration the valvetrain motion and angularity which is a function of the lobe shape or ramp. If you dwell in my last statement, you can figure out what is the source of the problem with the stamped rocker arms in Stock Eliminator.

[Jeff Goss]

Isn't that a function of duration? They way I understand it, you want the valve to open and shut as quickly as possible. Ideally, you would want the cam "ramp" to increase as steep as possible, then drop as quickly on the back side. This could cause the inherent "bounce" starting at the lifter and reverbrating through the valvetrain. If the spring couldn't keep up, you would get periods of increased lash as the valve tried to keep up. These harmonics cause the "beating" of the valvetrain.

I'm not the smartest tool in the shed, but it seems like when we started to vary duration in Stock, these problems started. I know Chevrolet motors aren't the only ones affected.

Jeff

[SSDiv6]

Originally Posted by Jeff Goss

Isn't that a function of duration? They way I understand it, you want the valve to open and shut as quickly as possible. Ideally, you would want the cam "ramp" to increase as steep as possible, then drop as quickly on the back side. This could cause the inherent "bounce" starting at the lifter and reverbrating through the valvetrain. If the spring couldn't keep up, you would get periods of increased lash as the valve tried to keep up. These harmonics cause the "beating" of the valvetrain.

I'm not the smartest tool in the shed, but it seems like when we started to vary duration in Stock, these problems started. I know Chevrolet motors aren't the only ones affected.

Jeff

Not duration, it is the lobe shape and ramp design. There are too many schools of philosophy among cam grinders on what does work and what does not work. I have heard the story of "opening and closing the valve as quickly as possible", which happens to be a tale. You design a camshaft for efficient filling and exhaust based on the particular engine specifications. A stocker cam for a big block Chevy will not work the same on a Mopar big block. One mistake made by racers is believing that all they need is big cylinder flow numbers. Big flow numbers do not mean anything if you do not have the velocity; a good cam is designed with parameters based on 275 ~ 300fps numbers.

[Chris Hill]

Jason,

It does not matter if the valve is hollow or solid, just the mass of the valve. But you can not ignore the stiffness of the valve itself. Some of the cup guys have tried very light intake valves, specifically very light heads of the valve. They ran into issues where the valve started to bounce off the seat due to the valve itself not being stiff enough when the valve hits the seat. You have to look at the entire valvetrain stiffness, including the cam bearing journals, bending stiffness of the camshaft between journals, valve stiffness, and valve seat stiffness. Generally, the least stiff member of the valvetrain is the rockerarm. And you only include roughly 1/3 of the mass of the rocker in your effective valvetrain mass. Some of your cup teams are using steel rockers instead of aluminum, as this drives the total valvetrain stiffness up without driving up the valvetrain effective mass.

Jeff Lee,

The beehive does help with decreased mass, but it also helps the valvespring harmonics issue. A beehive spring does not have constant stiffness and thus not a constant natural frequency. If a system does not have a constant natural frequency, harmonics are not as much of an issue. That is a very big reason nitrogen air springs are used in F1 and very high end motorcycle racing engines. Yes, air springs are light, but the very large decrease in valvespring harmonics is a big plus as well.

SSDiv6,

You may want to contact SAE about your proposed book, as I know they are looking for more valvetrain information. But then you would reveal yourself  A very old book exists by Michael Turkish that is the main valvetrain book I’ve read, plus internal research from my previous company. I know SAE recently published a book in the past couple of years about valvetrains, but I have not had an opportunity to view it yet.

On the poor angle issues on the small block MoPars and others, I agree the angularity will increase the force ratio in the valvetrain. For instance the rocker ratio may be 1.5, but the actual force applied between the pushrod and lifter cup may be 1.7~1.8. In my opinion, the increase in force ratio will increase the loading on the rocker arm, but not enough to cause rockerarm failure with out allot of lash and the subsequent impact loading. If you don’t believe me, take your peak valvetrain kinematic acceleration (generally during opening at approximately ¼ to 1/3 lift) and look at the stress on the rocker arm. You will find a pretty large safety factor for stress in the rockerarm. The only way to break it is impact stress.