metal compatibility roller rocker conversion

[e21jps]

We are designing a rocker conversions for a SOHC race engine. The operation is via finger follower style rocker with 2 rollers under the cam and one on the tip for the valve stem. I need help to find the best material compatibility for the rollers and pins. The cam roller runs directly on a needle bearing so I was thinking something like case hardened 8620 for both the roller and pin would be OK? Cam it self I'm not sure of exact grade, i think is 41xx... and induction hardened. Geometry and cam is all sorted we have spent a great deal of time and development into getting it designed correctly.

My main concern is the tip roller which runs directly on the pin with no bearing, similar to all your typical v8 style roller rockers and I need to find the best material and hardening process for these two components. Iv heard dissimilar metals are usually better. This is only splash fed with engine oil, i have included into the design some little oil tracks in the sides of the body to promote oil down to the pin.

the cam roller is 26mm x 10mm wide with 2mm open cage needle running on a 10mm shaft (pin)
the tip roller is 13mm x9mm wide running directly on a 5mm pin

Thoughts and comments greatly appreciated.

 

[tbuelna]

e21jps,

Whit any type of hertzian contact, like that of your camshaft roller follower or rocker roller tip, you should always try to equalize the contact stresses in both parts. With the contact between the roller follower and cam lobe, the roller follower will typically have a smaller radius of curvature than the cam lobe, except for contact across the nose of the cam lobe, and will also be subject to a greater number of load cycles than the cam lobe due to its smaller circumference. To minimize friction losses at the roller follower, it is best to have rolling contact between the cam and roller, and to have sliding contact at the much smaller radius interface between the roller and rocker pin.

The same applies with the contact at the rocker roller tip and valve stem. The reversing rolling contact between the roller tip and valve stem, produces less friction loss than the sliding contact at the smaller radius contact between the tip roller ID and the rocker tip shaft.

 

[pontiacjack]

e21- You knew it was just a matter of time, before I hijiacked your thread, right?!
I recently got far enough along with my OHC design to assign dimensions to my "fingers" and come up with ballpark worst-case tensile and shear stress requirements. It looks like I could get away with easy-machining 4130 (off-the-shelf wrought bar at about 30 -32 Rockwell-C). Comments?

 

[e21jps]

Hey all discussion is welcome, where i got to was considering 52100 bearing steel for both the rollers this is said to be great alloy with good durability and wear properties, i think its used with deep case hardening to about 60 Rockwell. For the tip roller pin something like 4340 through harden to around 43 Rockwell to maintain core strength, same material for the cam roller pin but since it has a needle bearing use a deep case harden up to maybe 50+ Rockwell

Anyone have thoughts on this combo??

 

[turbomotor]

You may want to consider M50 tool steel in place of the 52100 bearing steel.

http://www2.mae.ufl.edu/arakere/docs/STLE_spall_1.pdf

 

[TStaples]

If you want to take a page from the latest F1/INDY/NASCAR type valvetrain and engine tech, I would suggest either tool steel, or 52100 for both parts, and then have one of them DLC (Diamond Like Carbon) coated to provide a good bearing layer between them. Today's DLC coatings are both hard, and tough (interesting mix), and also provide their own lubrication. Most DLC's end up with some mix of sp3 bonded carbon (diamond), some sp2 bonded carbon, plus some hydrogen, interspersed in their outermost layer(s). The sp2 bonded carbon provides graphitic lubrication to the boundary when no oil film is present (i.e. startup), all but eliminating wear. I can personally recommend Industrial Hard Carbon, in Denver, NC. They market their coatings to racers and engine folks via a sister company called Extremion. Good stuff.

-Tony Staples

http://www.tscombustion.com

 

[pontiacjack]

So- any comments on my proposed use of 4130 for the bodies of the followers? Any concern about the areas where the two roller axles will seat in them- maybe need local harderning there? [I'm leaning toward a snug fit of the axles in the bodies, with retention by E-clips in grooves.]

 

[Tmoose]

"52100 bearing steel ...... is said to be great alloy with good durability and wear properties ". I think 52100's claims to fame are hardenability, which brings raises UTS and fatigue strength, and availability with high cleanliness with thus reduced likelihood of impurities to serve as fatigue initiation sites. Related to Hertzian stress is "contact stress" that is the heart of many ball bearing life calculations. Hertzian stress near ball/roller/race contact can be WAY higher than plane bearing stress, so even tiny material imperfections in the wrong place are going to reduce the stress cycle counts before cracking.

Maybe the tribological nightmare of skimpily lubricated steel-on-steel has proven to survive just fine in this application, but substitution of "ceramic" balls, still running on 52100 races, immediately brings life improvements related to disagreements that go on at the secret ball/race interface. The weaker the ElastoHyroDynamic lubrication, the more impressive the resistance of the mixed material combo to wear and damage becomes.

 

[pontiacjack]

I'm hoping to avoid needle bearings, which make an AWFUL MESS if breakage occurs in a race engine. I also hope to not "re-invent the wheel", so I was looking at Isky's description of their EZ-Roll roller lifters, which use micro-finish technology in place of needle bearings (forgive my over-simplification). Since they offer retrofit of EZ-Roll to earlier lifters, I fired off an email, asking if they might help me out- either sell me the EZ-Roll pieces for my use, or do the "fitting" of those pieces to the followers I'll fabricate. Here's hoping they respond...

 

[e21jps]

During my discussions with a metalurgest he indicated chromolly steels such as 4130 would be fine for the pin/shaft, I have gone for 8620 with a deep case harden for good core strength and hard surface for the needles. I have looked at the Isky EZ Roll, they have oil pressure fed through internal galleries to the pin so it operates just like a journal bearing which i think is essential to its success. It is possible to incorporate the same system into my rocker as i do have a pressure fed rocker shaft but it involves a lot of galleries and blind plug in the pin etc. much easier to just stick with well proven needles. I have seen a few articles about peoples adventures with an old overhead cam V8, ford i think? it had roller followers without a needle bearing and encountered countless failures between pins and rollers so a needle bearing really is the best solution for everything but the most extreme conditions. Some drag engines run over 750lb open spring pressure with 1.65:1 or greater rockers so thats 1,230lb up static on the lifter, not to mention the dynamic loads shifting lifters, pushrods and valves to 0.700" lift all at 8000rpm so its no wonder they start having problems! OHC applications typically have lower spring pressures, my application only has about 280lb static with a 1.4:1 rocker ratio 0.500" lift and no pushrods or lifters to move so im picking the needles will be happy all day.

 

[pontiacjack]

Isky has not yet answered my email. When (if) they do, I'll question them about the need for pressure oil delivery to the wheel/axle. If necessary, I could provide that, since my design already includes pressurized oil to the follower/ball-stud juncture. It would just mean a couple of passages drilled into each follower body.

 

[pontiacjack]

Oops... I forgot to respond to your comments:
Springs will be about 250 lb. seat and 575 lb. open (about .625" lift). Follower ratio will be within a whisker of 1:2. Maximum negative acceleration of lobe profiles will be limited to about 2.5 x 10^(-4) inches per cam degree squared. I'm building the engine (blown alky) to have good power up to at least 10,000 RPM.

 

[pontiacjack]

Today's telephone conversation with Ron Iskenderian was in stark contrast to my being frustrated at lack of a response from my emails to Isky Cams. I gotta' tell ya'- Ron exemplifies good customer service. We talked for more than a half hour, during which he displayed considerable engineering expertise- and also a genuine interest in my project (telling him how his dad Ed helped me out thirty years ago with my original M/T hemi sort of "broke the ice"). He is quite willing to sell me the EZ-Roll pieces and to work with me.

Neither the EZ-Roll nor EZ-Max lifters have internal oiling- "splash" is fine for all but extremely severe applications (1,300 lb. springs, etc.), in which case "dedicated" oil supply to the axle is recommended (but merely "aimed" near the axle is sufficient).