Has anyone installed a set of roller rockers in their engine? What make/model of rollers? How much $$$$ Were you able to install under factory valve covers? Were guides required? What, if any, performance gains were realized? Were there any negatives? Was the cost/benefit worth while?

 

Mac,

If you phone up Mopac on the King George HWY they will be able to help you with those. They are in Direct competition with Summit up here in regards to pricing. I believe that you can put 1.5's in with out doing any mods. If you go up to the 1.6's you will have to do a bit of work in regards to push rod clearance coming up through the head. Its minor mod but it will need to be done. The cutter I think was around $50. As for performance gain, you bet, anything you can do in your engine to reduce friction is a step in the right direction. Rollerize the world, baby :D

 

Have you actually installed a set, Ron? I was hoping someone could give a first person account of the experience and if the results were better than my first and only experience with rollers.

I assisted in putting a set into a drag car many years ago and it was a pain because we had to cut/edge and then install guides. Unlike the newer ones, the tips weren't rollerized, only the pivot was. The stock valve covers didn't fit so a new set had to be purchased.

There's no question about the friction reduction. Even with the rollers only at the pivot, the engine revved easier and higher. So much so, my buddy floated the valves on the first run and snapped a bunch of valve springs. It was close to the end of the season, so he packed it in.

Now you know why I asked so many pointed questions....

 

All I can tell you is that the performence gain is there not only because of friction. Stock are ok but they are very inconsent and have a lot of flex to them.

 

Unless you plan to spend a lot of time above 4000 revs, roller rockers will give very little return. Their primary advantage is lower oil temperatures and a reduction is the overhead oiling requirement. With the production ball rockers you probably have hydrodynamic lubrication under most circumstances, but it heats up the oil more. That's why many racing engines use roller rockers, but the difference in friction power dissipated is not that much.

Another example is replacing the journal bearings with rollers -not easy because the crankshaft has to be built up, but consider the example. The friction difference would not be the overriding consideration. The advantage of roller bearings is that you can eliminate the oil pump and just have splash lubrication. The big reduction in friction would be the power consumed by the oil pump.

Duke





[Modified by SWCDuke, 7:41 PM 12/9/2001]

 

I appreciate your reply, Duke, but I'm somewhat confused by it. I understand the rollers come into their own in the higher rpms, but if the difference in friction isn't much, why is the oil heated by the ball rockers and not the rollers? Isn't that heat from friction? Am I missing something here?


[Modified by Mac, 9:10 AM 12/10/2001]

 

Hydrodynamic lubrication is when a thin film of oil is formed by oil flowing under pressure between two surfaces with close tolerances. A cushion of oil constantly exists between the metal parts minimizing metal to metal contact. In fact, if the oil film can be maintained without interruption, there is ideally no wear at all. The downside is that friction resulting from the viscosity of the oil flowing under pressure and rubbing against the metal surfaces results in heat, which must be supplied by horsepower to drive the oil pump.

Splash lubrication is where oil is "splashed" onto the parts by the thrashing of the machine movement. This also creates an oil film between the parts to minimize meat-to-metal contact, but because the oil isn't under pressure within close tolerance constraints, the oil film is squeezed out and lost quickly. If it is not replaced immediately, then you begin to have wear. SWC said the advantage is that the power consumption of the oil pump is reduced by use of roller rockers, but that additional "power" required to pressurize your ball rockers is negligible.

On duh utha' han'...iffn' yuh put dem rolla' rockas' in dahuh, yuh might git sum "placeebo" effeck, an' afta'all it IZ dat "placeebo" effeck in da seat of yo pants dat yo iz lookin' fauh. :cool: :cool: :jester


[Modified by Chuck Sangerhausen, 7:34 AM 12/10/2001]


[Modified by Chuck Sangerhausen, 8:40 AM 12/10/2001]

 

There's got to be more to roller rockers than a placebo effect- what about the cool factor:cool: when I can tell all my friends about the wonderful racing technology I've stuffed under my valve covers.

 

Good question, Mac, and I hope I can give a worthy answer.

Chuck explained hydrodynamic lubrication, and it is essentially the same as "hydroplaning" on a wet road. It you have two surfaces with relative velocity between them, a viscous film will keep them apart. Engine bearings always experience hydrodynamic lubrication except during cranking. Rings are probably hydrodynamically lubricated except at the very top and bottom where they slow to zero velocity and reverse.

Rocker ***** are probably also hydrodynamic except at the very beginning of opening and closing where the relative velocity approaches zero. The friction power of hydrodynamically lubricated bearing is due to the shearing of the oil film, which heats up the oil. Though some heat is transferred to the surrounding stucture, most of it is carried away with the oil as it escapes the bearing. A roller bearing also shears the oil, but there is typically more surface area for the structure to carry away the heat, because roller bearings are almost always phsically larger and have more total surface area for heat transfer than a journal bearing designed to carry the same load.

As a general rule, a high revving engine - such as racing engine - will see a reduction in oil temperature when switching from ball to roller rockers, but the difference in power is minimal except at very high revs.

A better bet than roller rockers would be 1.6:1 rocker arms. Based on my measurements the typical actual rocker ratio of the OEM rockers is 1.44, not 1.5, and it varies. It begins at about 1.37 when the valve just starts to open and maxes out at 1.44 at high lift. The 1.6 ratio aftermarket rockers are not constant either, but I assume they max out at 1.55.

When I run engine simulations on my PC I input 1.44 as the actual rocker ratio, but changing that to 1.55 with the same cam gives a meaningful increase in mid and top end power, without any significant effect on low end torque.

On a street engine, where you're looking for more top end power without installing a cam that will kill the low end torque 1.6 ball rockers are worth considering, but you might have to open up the pushrod holes to run them without the pushrods scrapping the head passages.

When I took my first engine design course as an undergraduate I engaged my professor in a conversation about the friction characteristics of roller versus journal bearings. My thought at the time was that roller bearings, as used on contemporanious Honda twins of that era (late sixties) were lower friction than equivalent journal bearings. My professor went to great lengths explaining to me that was not true, and I ended up understanding that the built up crank with roller bearings and no oil pump was a design decision made on the basis of manufacturing cost and simplicity. My current CB1100F has journal bearings, but it revs just about as high as my erstwill roller bearing CB 160 and SL 350.

At very high relative velocities, journal bearings do begin to generate excess friction, and one way to reduce friction is to go to a lower viscosity fluid. You can actually make a journal bearing using air as the "lubricant" and some gyroscopes used in aerospace applications have air bearings, but there comes a point where the combination of relative velocity, journal size, and loading dictate a roller bearing, and such is the case with the shafts on turbine engines.

Duke

 

Beats me, but I took a set of Cranes OUT of my BB and put in the stocks. Stock engine, stock parts. Did the same with the distributor.

 

Duke, confirming what you said on relative velocity and journal size, it can be noted that small gas turbines like those used for aircraft have relatively small diameter shafts and use rolling element bearings; probably roller bearings with a duplex or triplex ball bearing for the thrust bearing.

Larger industrial gas turbines (not aircraft derivatives) used for power generation use journal bearings, but the shaft journals may be 8" in diameter or larger. Small gas turbines may scream up to 15,000 to 20,000 rpm. The limitation, of course, depends on the rotor tip diameter and strength of the blade material. I can remember no large industrial type gas turbines that exceed about 6000-8000 RPM.

 

Interesting discussion! Big Pontiac V-8's in the early 60's had very large-diameter main journals (ostensibly for durability), but failed bearings frequently in race applications; they finally figured out that the very large diameters resulted in very high circumferential speeds at the journal/oil film/bearing interface, which heated the oil excessively, leading to bearing wear and failure of the oil film to carry the loads. Guys who raced 421's and 455's seriously had the main journals machined down and used spacers with 326/389 bearings to cure it.

An article in this month's Car Craft (I pitched it last week after reading it, so I'm going from memory) has a good dyno comparison of several types of rockers, just to answer the questions posed above. They started with stamped rockers, then Comp Cams 1.52:1 Magnum roller-tip rockers, then full-roller Comp Cams stainless rockers, and did some ratio-changing as well. The Comp Cams roller-tip (only) Magnum rockers came up as the best deal for the money, gaining 4-8hp depending on rpm, and going up to 1.6:1 rockers actually lost power and torque. I've used several sets of Comp Cams roller-tip Magnums on other project cars, and they fit under stock valve covers on both SB Chevys and SB Fords - I don't think any others will.

 

Interesting, Chuck! I was never aware that industrial gas turbines used journal bearings. I would think that a six to eight inch shaft running at 6 to 8K revs would have too high a tangential velocity and create the kind of problem that John mentioned with the Pontiac V8, but maybe they run free floating bearings like on a typical automotive turbocharger which would bring down the tangential velocity to acceptable levels (?).

Duke

 

Now that you mention it, I think they may actually use longitudinal tilting pad "shoes" that pivot on a ball in the center of the back of the pad. Seems like there were about six of them to a journal. The thrust bearing is typically a "Kingsbury" thrust bearing that has like six or more stationary segmental shoes on each side of a thrust disc that is machined into the shaft (bugger one of those babies, and you get real creative to keep from having to replace the entire shaft). These thrust "shoes" or pads were also free to tilt and move individually.

I could be over-enthusiastic on the 8,000 RPM (my intent was to give an order of magnitude comparison to aircraft turbines), but I remember well plotting compressor maps with speed lines up to 6000 RPM and above.

Typically, heavy industrial machinery has journal bearings. One reason is ease of service. On industrial gas turbines, the journal bearings are located outboard of the turbine unit proper, and can be changed relatively easily by removing the bearing cap, removing the shaft weight off the bottom half and rolling it out around the shaft much like you would change a rear main seal in an "old" small block chevy. A bearing failure in an aircraft turbine is another matter because the bearings are buried deep inside the rotating parts. Bearing failure means a total tear-down.

 

As usual, my questions were answered completely and the additional information provided both excellent examples and food for thought. Thank you to all.

 

Now this explaination I can understand! :lol: