roller rockers vs contact tip rockers

[jsgarage]

I was told decades ago not to expect a horsepower advantage from roller rockers; the gains are in less valvetrain friction during running and thus less oil heating. Sometimes, enough oil temp improvement results to not need an oil cooler in shorter endurance races. Significantly, when Ford rollerized their rocker arms for the NASCAR 351-C, the trunnions on each stud mount were all that got needle bearings. The valve stem tip was still sliding-contact from stock hi-ratio stamped steel 1.73:1 rockers. And one really cannot compare rocker arms on OHC engines vs pushrod engines.

[hoffman900]

I disagree with that statement. They perform the same function and are of similar design. Jesel makes roller tipped rockers for Esslinger OHC heads and the Ford Mod motor.

[twl]

My simplified opinion is this:

If the tips actually do roll, they are better than sliders.
If the tips don't roll, then they are just as good as sliders.

I don't see any scenario where rollers are worse than sliders.

[pamotorman]

I was told decades ago not to expect a horsepower advantage from roller rockers; the gains are in less valvetrain friction during running and thus less oil heating. Sometimes, enough oil temp improvement results to not need an oil cooler in shorter endurance races. Significantly, when Ford rollerized their rocker arms for the NASCAR 351-C, the trunnions on each stud mount were all that got needle bearings. The valve stem tip was still sliding-contact from stock hi-ratio stamped steel 1.73:1 rockers. And one really cannot compare rocker arms on OHC engines vs pushrod engines.

i believe ford sold conversion kits that converted the rockers to ball bearings.

[Newold1]

Could it be that it is easier to build a roller tip for a rocker, polish and heat treat it to minimize wear and friction at the contact point on the valve tip than it is to manufacture an entire rocker body, with a special formed sliding tip with its required polishing and hardening at that tip?
Little rollers on a simple shaft are quick and easy to use for a roller tip rocker and provide a simple minimum contact point for the slide and they do sound cool to the enthusiast and allow a higher selling price don't they?!

[Walter R. Malik]

Most of the roller tip advantages involve the lack of valve stem side loading or being "forgiving" enough that the geometry does not need to be exactly correct.

[DaveMcLain]

If everything is just about right with the valvetrain and rocker design wouldn't it be possible for the rocker arm to "rock" on the end of the valve stem with little to no sliding action needed as the valvetrain actuates through a reasonable amount of lift?

[Walter R. Malik]

If everything is just about right with the valvetrain and rocker design wouldn't it be possible for the rocker arm to "rock" on the end of the valve stem with little to no sliding action needed as the valvetrain actuates through a reasonable amount of lift?

It surely does ... and that is correct and how it is supposed to be with a NON roller tip on the rocker and it NEEDS to be almost exactly correct for any kind of valve stem / guide longevity. A roller tip rocker arm does not NEED to be this exacting.

[turbo2256b]

Most of the roller tip advantages involve the lack of valve stem side loading or being "forgiving" enough that the geometry does not need to be exactly correct.

The slipper tip is more forgiving geometry wise. One of the reasons roller tips were not used in production engines often.
Have done many valve train stack ups on cad to design rocker arm/ valve train set ups. Found lots of interesting things about rocker geometry as well as bucket tappet and roller follower issues.

[andyf]

Roller tips aren't about friction, they are a necessity when you have an aluminum rocker arm. It is much easier for the aftermarket to make aluminum rocker arms and put a hard steel roller tip in it that it would be to tool up a slider type rocker arm. If you are an OEM then you have enough scale to go ahead and build the tooling to produce a slider type rocker arm with the proper material and heat treating to work.

It is hard to find slider type rocker arms for most engines. Crane used to make some nodular iron rocker arms but they went out of business. Erson went out of business. Isky stopped making them, etc. I think Jesel has enough money and capability that they could make steel rockers with sliding tips if they wanted but they must not want to. Either they don't work as well or their customers don't want them. I don't know the answer to that, someone from Jesel would need to chime in and tell us.

[Paul Kane]

The main question posed in this thread, and the majority of replies posted, seem to address to a very common misconception about roller-tipped rocker arms: that the primary purpose of the roller tip is to "reduce friction." But friction reduction is not the primary reason for the addition of the roller tip.

The primary purpose of the roller tip is to maintain the loads/forces directly in-line with the valve stem while the rocker arm articulates though its radial sweep.

The best analogy I've heard is one that Jim Miller expressed: "imagine extending your arm out straight, horizontally, as though your shoulder is the pivot point like a rocker arm trunnion and your closed fist is the roller tip's axle. Now, from your closed fist hang a weight from a piece of string (the weight at the end of the string represents the roller diameter contacting the valve tip below). As you raise/sweep your arm up and down (radially) while pivoting at your shoulder, the string remains vertical with the ground. This shows how the force of the roller tip against the valve stem is pointed directly in line with the valve stem and reducing the so-called "side-loading" of the valve guide."

By way of comparison, a shoe-tipped rocker arm imposes more for-and-aft side loads upon the valve stem (imagine the same extended arm exercise with your flat open palm representing the shoe-tip, and pushing against the valve stem from an angle). Further, shoe-tipped rocker arms "change ratio" throughout their radial sweep since the trunnion-to-contact pad dimension gets longer as the contact pad crosses the valve stem...similar to the sole of a shoe while taking a step, from heel to toe (and back).

Friction reduction from the roller tip--if even measurable--is a side-benefit of the roller tip, not its main reason for being there. (Most friction reduction comes from the caged bearings at the trunnion.)

[Walter R. Malik]

Most of the roller tip advantages involve the lack of valve stem side loading or being "forgiving" enough that the geometry does not need to be exactly correct.

The slipper tip is more forgiving geometry wise. One of the reasons roller tips were not used in production engines often.
Have done many valve train stack ups on cad to design rocker arm/ valve train set ups. Found lots of interesting things about rocker geometry as well as bucket tappet and roller follower issues.

If you say so ... I will respectfully disagree especially when it comes to sideways forces.

[Zmechanic]

Friction reduction from the roller tip--if even measurable--is a side-benefit of the roller tip, not its main reason for being there. (Most friction reduction comes from the caged bearings at the trunnion.)

I would say that's also easily provable when you consider that if there was any significant friction between the rocker tip and valve stem, how could you expect that actually be durable and not chew up one or both of them in short order.

But wouldn't the side loading of the stem come from this same friction force if it were present?

[turbo2256b]

Side loading if your meaning forces not in line with rocker movement aligned with valve push rod reduction is best alleviated in rocker shaft designs inwhich twisting of the rocker is reduced about as much as possible.

Canted valve setups can be one of the worst to figure out as its kinda a 3D motion not a 2D motion.

Some rockers like fords rail rockers were designed to limit rocker twist some of todays roller tips do something like the rail rockers with washers either side of the roller tip

[hoodeng]

In the 90's a valve train manufacturer produce roller rockers with rocker shaft needle rollers installed as well [heavy series Torr], after extended use they became quite noisy , on disassembly it was found the shaft needle rollers had trenched the shaft , there were two fix's , one was to retro install the original bush type assembly with new shafts ,the other was to install needle rollers with a higher roller count [std series Torr]. The issue was in the original assembly ,the rollers were not rolling over the roller in front or behinds path in operation hence trenching the shaft ,so the higher roller count enabled this to happen and extended the life of the part, i have yet to see a punch the air moment on the dyno with the installation of these parts , some guys just want them ,and that is that,it's their invoice.

Cheers.