Roller Rockers & Adjustable Valvetrain FAQ

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gonridnu
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Roller Rockers & Adjustable Valvetrain FAQ

Post by gonridnu »

As I have stated before I was the sales manager for T&D Machine Products for almost a decade. They are a manufacturer of high end shaft rocker sets and supply half the Nascar teams as well as a majority of the sprint car and sportsman/pro drag racing markets. They are a direct supplier to Mopar Performance and several well known names like Carrol Shelby, Lingenfelter and Duttweiler. In my position I worked hand in hand with engineers in our facility and those in the engine departments of teams like Hendricks and Evernham. Our rocker sets with few exceptions started in the $1000 range and went up to $5000 for a single engine.

Because of the help I have received here I thought I would give something back and write a diatribe on rocker arms in hopes it will help clear some questions up.

Roller rockers can be broken down into two basic groups, stud mounted and shaft mounted. Within those two groups you can have variations which would be roller trunion, roller tip, and rockers with both roller trunion and tip. Most shaft mounted roller rockers are both roller trunion and roller tip. Many stud mounted rockers utilize both a roller trunion and tip, but there are some budget stamped steel rockers that use only a roller tip, you usually see these in small and big chevy applications.

Shaft mount rockers are the cream of the crop. There are four basic types. Those that use a single mounting stand that spans the head, paired trunion rockers in which there are pairs of rockers per cylinder that generally bolt to the stock pedastals, single stand/rocker per valve, and a single shaft per head arrangement that is most often found in production vehicles such as Mopar and Volkswagen.

The advantages of shaft mount rockers are that a rocker mounted on a stationary shaft does not twist and the trunion does not move up and down like a stud mount rocker does when las is experienced. To be more clear a stud mounted rocker on a non-hydraulic lifter will actually drop down the stud when it experiences a lash condition on the base circle of the cam. When it rises back to the top and hits the poly lock itwill actually bounce and cause an eratic valve opening motion which shaft mounts do not because the trunion is stationary. Another advantage to shaft mount rockers is you can offset the pushrod and roller tip up to a couple of inches in order to clear large ports. Here is a picture of my B-1 engine that employs .800" of pushrod to roller tip offset.
DSC00050.JPG
Another advantage of shaft mount rockers is that when they employ a stand that spans the head it ties all of the mounting points together with a single bar thus further stabalizing the valve train because under high spring loads an indvidual pedastal will deflect. By using a stand with small mounting holes outboard of the rockerthey are able to use much smaller shafts than their stud mounted counterparts that must not only provide a shaft for the rocker to ride on but also one that is strong enough to have a large hole through the middle of is to accomodate a stud. The smaller shaft allows for more material between the adjuster screw and the trunion hole in the rocker (more on this later)

The only real disadvantages of shaft mounts is they often require advanced machine work to the top of the head to accomodate the stand, moreso on canted valve heads than wedge or common angle heads and they are expensive. OEM style single shaft arrangements are a pain in the ass to mount (getting 8-12 rockers all in the correct position while mounting the shaft requires 4 arms) and the shafts can break easily when mounting if they are flexed too much.

Stud mount rockers as commonly seen on performance and factory engines are a marginal improvement over non rollers. As mentioned previously they experience a lash condition induced bounce on solid cams, They cannot accomodate offsetwithout twisting, their trunion holes are large which reduces the amount of material betweeen the adjuser and the trunion, they require guideplates and hardened pushrods, and to stabalize them under high spring loads they require stud girdles. They do however offer the advantages of a roller tip and trunion as well as adjustability.

Continued on next post....
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Re: Roller Rockers & Adjustable Valvetrain

Post by gonridnu »

Adjustable rockers.....

The necesity for adjustable rockers is to either create the correct amount of preload on a hydraulic lifter or to create the correct amount of lash on a mechanical or solid cam. In most applications hydraulic lifters need to be preloaded .045" to .075" to operate correctly however many racers in hydraulic classes will run as little as .010" with a hydraulic lifter that has a very stout retaining device to keep the plunger from pushing out the top of the lifter. Honestly they are best suited for mechanical roller and flat tappet cams and have been the norm for almost a hundred years in those applications.

Solid lifter cams have a small ramp that is built into them that takes up a majority of the lash before the valve opening event. Hydraulic cams do not. Obviously an adjustable rocker on a solid cam also has the ability to be adjusted in order to account for the expansion of block and heads as they heat up. Many high end racers know the amount of thermal expansion of their block and heads as well as cam ramp and optimize their lash settings so that they are near zero lash on the base circle of the cam, thus gaining the maximum lift and duration out of their cam. The rest of us base our lash adjustment off of the cam manufacturers recommendation which has some safety margin built into it in order that the valves fully seat.

Hydraulic lifter cams are basically self adjusting in so far as the hydraulic lifter maintains a zero lash condition while on the base circle of the cam and then opens the valve when the hydraulic pressure overcomes the spring pressure. For this reason many manufacturers see no need for an adjustable valve train as the hydraulic lifter is an "automatic adjuster". Our 4.0 engines as well as many fords and chryslers and a slew of others use pushrod length to achive the preload on the lifter and provide for no adjustability as it not required.

To this end I would ask everyone that is considering an adjustable rocker if they are using hydraulic or mechanical lifters. If they are using hydraulic lifters than we must ask why they feel the need for adjustable valve train when the selection of the correct pushrod length will achieve the same thing?

As a side note the NASCAR teams no longer use adjustable rockers but have opted to use pushrod length and varying thicknesses of lifter pushrod cups to achieve desired lash, thereby improving their MMI numbers by eliminating the adjuster screw from the rocker arm....I'd post a pic but I'd probably go to some kind of disclosure hell:)

Continued on next post....
Last edited by gonridnu on March 20th, 2010, 12:07 am, edited 1 time in total.
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Re: Roller Rockers & Adjustable Valvetrain

Post by gonridnu »

Aluminum vs. Steel.

Aluminum roller rockers are perceived to be lighter than steel because we all know aluminum is lighter than steel. But is a pound of aluminum lighter than a pound of steel? The fact is that it takes a greater amount of aluminum to achieve the same deflection rates than it does steel. We have all seen the size of our stamped steel 4.0 rockers and the size of an aluminum roller rocker but have you taken into account the material mass difference between the two?

The measurement of the rotational and inertial forces required to move and then stop (and then move again) an irregular shaped object around an axis is called "mass moment of inertia". The greater the distance of weight from the axis of rotatation the greater the force. Aluminum rockers have a great deal of material above the trunion in order to maintain rigidity vs. our stamped steel rockers where most of the mass is below the axis of rotation, but still affects MMI. So while aluminum is a lighter material there is greater mass at a distance that is further from the axis thereby negating a great deal of benefit of the lighter material. If a steel rocker can achieve superior deflection rates in a more compact design it can have better mass moment numbers and appear lighter to the engine. In the past 5 years all of the NASCAR teams have moved to steel rockers for this reason. Better deflection rates with similar or better mass moment of inertia numbers.

Aluminum vs. Steel in endurance or steet applications...... All aluminum rockers have a fatigue life. Upon initial use there is a microscopic fracture that originates in the root of the second thread near the bottom of the adjuster hole. How long it takes for that fracture to work it's way to the trunion bearing hole is dependant on several factors. Spring pressure, Rate of lift, valve weight, cylinder pressure (on the exhausts), and RPM are amongst those factors. Eventually all aluminum roller rockers will break in this area. Exhaust rockers will invariably break first because they open against cylinder pressure. Once broken the exhaust valve fails to open which can lead to catastrophic engine damage above and beyond what the pushrod and lifter create flopping around because a cylinder can fill with unburnt fuel and "hydraulic" causing rod failure and lifted head gaskets.

Steel on the other hand, specifically 4140, 4340, and 8740 is basically harder than the gates of hell and is an excellent choice for endurance or street application. It is basically unbreakable by any real world forces encountered in an internal combustion engine.

To this end I would ask the question, what is your intended usage of this engine? If it is a street or endurance engine I would highly recommend steel over aluminum. Most people would be willing to accept a slightly heavier rocker knowing the service life would be greatly extended.

Continued on next post....
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Re: Roller Rockers & Adjustable Valvetrain

Post by gonridnu »

Roller rockers....(Ithought he'd never get to this:)

For starters roller trunion rockers offer the greater reduction of frictional forces than do roller tip rockers. For this reason you will see many OEM's that now offer roller trunion rockers that have solid tips. As the trunion is the fulcrum point of the lever it bears the brunt of the load. Roller trunions invariably utilize a roller bearing to carry the load however ALL low end roller rockers and most high end rockers utilize a roller that rolls on a solid shaft without the aid of a bearing.

The reduction of friction can result in some minimal gain in HP and lower oil temps due to reduced friction. These gains are directly proportional to the amount of spring pressure the rocker arm is working against, but do not amount to very much under most conditions.

How much of reduction? Well I honestly have had several drinks and can't remember the exact number but bear in mind that a non-roller trunion is moving on a film of oil which has a pretty good coefficient of friction so it's not a lot. It is however exhaserbated by high spring loads because it is not pressurized oil. For this reason a roller trunion will become advantages at some point. Our 4.0 motors, unless fitted with a solid roller cam, or solid flat tappet with extreme loads, will have nowhere near the spring pressures to realize any real gain from a roller trunion and I would guesstimate the frictional reduction in the rocker arm area to be well under 3% given the normal spring pressures of a hydraulic cam.

Roller tips..... As I stated before roller tips realize even less friction reduction than roller trunions. What they do achieve is less deflection of the valve under high spring loads. They also aid in the optimization of lift based on the arc of travel in high lift conditions. Very high end roller rockers utilize tips that ride on needle bearings on a solid shaft. These were developed by the nascar teams to reduce the deflection of thin stemmed valves as the roller tip rolled across them. They are only available on very high end shaft rockers. In the event you were running 8mm or smaller valve stems (like our 4.0's) under high spring loads they will provide you with reduced valve stem deflection.

Bearing these factors in mind I would ask you what your spring loads are and what you hope to achieve by running a roller rocker....

Continued in next post....
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Re: Roller Rockers & Adjustable Valvetrain

Post by gonridnu »

Valvetrain geometry.....

This is a term that gets thrown around a lot but few people, including many professional engine builders (trust me on this one), have a real grasp on it. The basic parameters that affect it are the fulcrum length of the rocker, the design ratio, and the relationship between the tip height, the fulcrum, and the pushrod end of the rocker.

Because a rocker arm travels in an arc it is never the same ratio at any given point withn that arc. Without a diagram I can only explain it in the following manner..... If the rocker is in a normal operating position it will yield "X" ratio. If you were to rotate it 90 degrees from the normal operating position it would move more in a horizontal axis than in a vertical axis and would thus yield substantially less actual lifting of the valve relative to lateral motion. Because a rocker travels in an arc "design ratio" is a critical component relative to actual lift. Rockers are designed to lift "X" amount based on their position and intended usage. for example a Big Chev rocker will likely be based on .750" lift when in a specific rotational position found on a big block Chevy. .750" because most performance cams are going to be .100" less or greater than the design lift thereby creating a nominal affect on ratio.

Fulcrum length is also a critcal component of "valvetrain geometry". Fulcrum lengths on most rockers will range from 1.380" to 2.00". A rocker arm is a lever and the relationship between the item being lifted (the valve) and the pivot point (the trunion) is called the fucrum length. Based on the fulcrum length and ratio the pushrod location can be determined using the formula "fulcrum length divided by ratio = pushrod distance from fulcrum". The fulcrum length is typically determined by the mounting position of the fulcrum relative to the tip of the valve and the ratio position adjusted accordingly.

As an example a 1.70 small block Chevy rocker utilizes a 1.450" fulcrum length rocker which has a pushrod position that is .852" from the fulcrum whereas a big block Chevy rocker that with a 1.70 utilizing a 1.650 fulcrum will have a pushrod position of .970" from the fulcrum or pivot point.

These dimensions and the acceptable variance of them is determined by the head package. The fulcrum lenght and pushrod location spcifically will be determined by what can fit in a given casting.

More valvetrain geometry next post....
Last edited by gonridnu on March 20th, 2010, 2:03 am, edited 3 times in total.
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Re: Roller Rockers & Adjustable Valvetrain

Post by gonridnu »

More valvetrain geometry.....

OK....so we know that the distance from the mounting point to the valve determines the fulcrum length and the fulcrum length is directly related to the mounting points and the pushrod position.....would you get to the point?

Yes....No...Maybe. Before I relate this to 4.0's I want to further explain a little more about geometry. The longer the fulcrum of the rocker the less distance the tip of the rocker will travel to achieve a given lift and the smoother the acceleration and deceleration of the valve.

Remember the tip is travelling in an arc because it is pivoting around the fulcrum point. The greater the length of the arm the less the lateral movement in a specified amount of lift. The reduction in lateral movement equates to less lost energy and less friction imposed by side loading. Because of the longer fulcrum length it also equates to less energy used to lift a required amount. In other words, the longer the breaker bar the less you have to push on it.

A longer fulcrum length also equates to a less violent opening and closing of the valve. The shorter the rocker the faster it accelerates and decelerates through the travel of the rocker and vica versa.

Another added benefit of a longer rocker, particularly in an aluminum rocker situation, is that the longer fulcrum equates to a greater distance from the trunion bearing to the adjuster screw, which equates to a longer sevice life.


Continued in next post....
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Re: Roller Rockers & Adjustable Valvetrain

Post by gonridnu »

Even more valvetrain geometry......

The proper tip motion across the valve is crucial to guide life. 99.9% of all applications benefit from a rocker tip motion that has been patented by the name of "mid-lift theory". Mid-lift theory states that the tip of the rocker arm starts to the inside, or fulcrum side, of the valve tip and travels to an equal distance to the opposite side of the tip at mid lift where it then stalls and returns to the starting point at full lift. As the valve begins to close the tip of the rocker then moves back outward past midpoint an equal distance to it's final inboard and original resting point when the valve is closed.

The only exception to mid lift theory is engines that incorporate very high spring loads (ie. pro stock applications) in which the majority of tip movement is realized prior to extremely high spring loads leaving the final 50% of valve opening in a vertical motion. This theory is utilized primarily by Jesel shaft rockers for high lift Pro Stock applications in which 1100 lbs of open pressure is required.
Last edited by gonridnu on March 20th, 2010, 1:44 am, edited 2 times in total.
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Re: Roller Rockers & Adjustable Valvetrain

Post by gonridnu »

I did some prelimnary measuring (would love someone to CMM the stock rocker) and it appears to be a fairly long fulcrum length, perhaps 1.750" which compared to a short rocker would mean it has a less violent opening/closing rate, requires less force to open/close, and has less tip movement, and utilizes the self adjusting nature of a hydraulic lifter with a low mass moment of inertia.
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Re: Roller Rockers & Adjustable Valvetrain

Post by gonridnu »

What does all this mean to me on my 4.0 stroker?

Adjustability of a rocker on a hydraulic lifter camshaft is of little concern as the lifter adjusts for thermal expansion of the components. Few of us exceed the RPM potential of a hydraulic lifter (approximately 6000 - 6500 RPM)

A good portion of us are running hydraulic cams that do not have high spring pressures so the frictional gains from roller valvetrain are minimal.

Because most of us are using these vehicles for street/endurance applications a steel rocker is preferable to an aluminum rocker. The high RPM weight savings of an aluminum rocker do not offset the need for the reliability of a steel rocker.

The long fulcrum length of the stock rocker reduces side loading of the guide and provides a smooth opening and closing action.

Most off the shelf roller rockers are shorter than the stock rocker and do not have the correct geometry to be used on a 4.0 inline 6

One last note....There is evidence that because a roller tip rocker used in a hydraulic application never experiences a lash condition the roller tip does not rotate. This means the roller tip does not re-clock and can develop a flat spot on the roller where it is in contact with the valve in the same spot over and over again.

There will always be applications where due to high RPM or high spring load a roller rocker is preferable to the stock rockers but for most of the people I've seen on this site the stock valvetrain is hard to beat and the expense of creating an adjustable roller valve train could be better spent on other performance modifications.
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Re: Roller Rockers & Adjustable Valvetrain

Post by unlimitedrubicon »

Nice work... Really has me thinking now... Thank you for the information.
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Re: Roller Rockers & Adjustable Valvetrain

Post by go4lo »

Wow!!!!! That's a lot to take in....thanks for the indepth write up.

I'm on the fence for my stroker build about whether or not to use stock stamped rocker arms vs. the harland sharp rollers. What are your thoughts on the stock rockers with the Mopar Performance springs that most of us on here are running?
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Re: Roller Rockers & Adjustable Valvetrain

Post by gonridnu »

By the time you get done with guide plates, machine work, pushrods, studs and the Harland rockers you'll be 500+

If it's a hydraulic cam engine you do not need the adjustability, but if it is a solid lifter cam you will. I am not a proponent of an aluminum rocker on daily drivers, and it appears Crower makes a stainless rocker so if I were going to put roller rockers on a driver I would choose them for their cycle life.

I don't want to discourage anyone from buying someone's products. Harland makes a decent rocker as does Crower, and it is great they have something for our engines It is really a matter of intended usage....
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Re: Roller Rockers & Adjustable Valvetrain

Post by go4lo »

gonridnu wrote:By the time you get done with guide plates, machine work, pushrods, studs and the Harland rockers you'll be 500+

If it's a hydraulic cam engine you do not need the adjustability, but if it is a solid lifter cam you will. I am not a proponent of an aluminum rocker on daily drivers, and it appears Crower makes a stainless rocker so if I were going to put roller rockers on a driver I would choose them for their cycle life.

I don't want to discourage anyone from buying someone's products. Harland makes a decent rocker as does Crower, and it is great they have something for our engines It is really a matter of intended usage....
I was under the impression from other posts and Harland Sharp that the 2 sets of pedestal mount roller rockers they sell for the 4.0L were bolt on. No machine work needed. Part numbers are S40196 and S40196A, http://www.harlandsharp.com/amc_jeep_olds.htm. Am I missing something?
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Re: Roller Rockers & Adjustable Valvetrain

Post by gonridnu »

No, it is I that was missing something. Could have sworn the page I looked at showed an adjustable rocker and gave a .400" machining requirement. In fact, I went and found it.... http://www.harlandsharp.com/inlineford_amc.htm apparently they have multiple sets

OK...so if you are indeed able to install without guideplates (no arguement here as I do not know and hardened pushrods to make an informed decision you need to know the deflction rates of the stock rocker and the H/S aluminum rocker. Some factors to consider when choosing....

1. The HP increases are going to be absolutely minimal from friction reduction with low spring tension
2. The additional RPM available due to an aluminum rocker that might have a lower MMI number is only going to become a factor at higher RPM's
3. The stock valvestain is proven to last 100's of thousands of miles. There is no aluminum rocker that can have that kind of service life or even half of it

So what is the difference between the standard part number and the "A" part number that has a higher price
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Re: Roller Rockers & Adjustable Valvetrain

Post by unlimitedrubicon »

The difference is the "A" is adjustable...
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