roller rockers vs contact tip rockers

General engine tech -- Drag Racing to Circle Track

Moderator: Team

plovett
Expert
Expert
Posts: 871
Joined: Sat Dec 30, 2006 3:49 pm
Location: Kansas City

Re: roller rockers vs contact tip rockers

Post by plovett »

The rocking chair analogy makes no sense to me. As the rocking chair rotates, a different part of the chair is continuously meeting a different part of the floor. But if a rocker arm rotates along a fixed point on a valve stem, that it totally different. A different part of the rocker arm is continuously meeting the same part of the valve stem. No?

paulie
User avatar
panic
Guru
Guru
Posts: 2295
Joined: Sat Dec 11, 2004 12:04 pm
Location: Ecbatana
Contact:

Re: roller rockers vs contact tip rockers

Post by panic »

Different chord of the pallet contacts different location on the stem tip, but there is always sliding contact + rolling contact.
plovett
Expert
Expert
Posts: 871
Joined: Sat Dec 30, 2006 3:49 pm
Location: Kansas City

Re: roller rockers vs contact tip rockers

Post by plovett »

panic wrote: Fri Dec 15, 2017 6:30 pm Different chord of the pallet contacts different location on the stem tip, but there is always sliding contact + rolling contact.
That's what I'm thinking.

Rolling contact is sliding contact.
Walter R. Malik
Guru
Guru
Posts: 6353
Joined: Tue Jul 24, 2012 11:15 am
Location: Roseville, Michigan (just north of Detroit)
Contact:

Re: roller rockers vs contact tip rockers

Post by Walter R. Malik »

plovett wrote: Fri Dec 15, 2017 6:19 pm The rocking chair analogy makes no sense to me. As the rocking chair rotates, a different part of the chair is continuously meeting a different part of the floor. But if a rocker arm rotates along a fixed point on a valve stem, that it totally different. A different part of the rocker arm is continuously meeting the same part of the valve stem. No?

paulie
NO ... the contact point on the valve tip moves from inside to outside, as the valve lift increases; minimizing scrubbing.
http://www.rmcompetition.com
Specialty engine building at its finest.
BILL-C
Expert
Expert
Posts: 746
Joined: Thu Feb 07, 2008 9:57 pm
Location: Oakville, CT
Contact:

Re: roller rockers vs contact tip rockers

Post by BILL-C »

Walter is correct. Notice the pear shaped rocker tip on those beautiful Del West rockers on page 5?
Carlquist Competition Engines
BILL-C
Expert
Expert
Posts: 746
Joined: Thu Feb 07, 2008 9:57 pm
Location: Oakville, CT
Contact:

Re: roller rockers vs contact tip rockers

Post by BILL-C »

What standard are we all using to define " no scrubbing action across valve tip"? .00001"?, .001?, What you can see with your eye? Valve guide clearance? I suspect not everyone is using the same definitions.
Carlquist Competition Engines
hoodeng
HotPass
HotPass
Posts: 1092
Joined: Sat Mar 04, 2017 6:53 pm
Location: South Australia

Re: roller rockers vs contact tip rockers

Post by hoodeng »

I'm not sure at what level i am operating at after seeing some serious science bought into this subject!! [my skill set doesn't look too high though].
I recondition V twin rockers with a simple Trock Cycle tool that i have had since we stopped pedaling generators , it simply allows the rocker to swing through its arc and holds it stable so a grinding operation can take place ,a final polish and they are done , i have seen rockers i faced thirty years ago and there is no detrimental conditions bought about by extended use after using the grinding process . The tool leaves a true 10.5mm radius on the pad with a 1.62:1 ratio rocker . All the old rockers show slide wear on approximately 5mm of the arc with a .500" lift 8mm valve, with a footprint of approx 2-3mm on the stem.
To generate a compound radii as proposed by some would necessitate a plotted rolling jig using two sets [or more] of centers for the shape to be generated [or an NC grinder which is above my pay rate] .
I think i will stay with simplistic.
You do not have the required permissions to view the files attached to this post.
User avatar
midnightbluS10
Expert
Expert
Posts: 933
Joined: Sun Oct 20, 2013 8:41 am
Location: Shreveport, LA

Re: roller rockers vs contact tip rockers

Post by midnightbluS10 »

BOOT wrote: Tue Dec 05, 2017 3:55 pm Roller tips sell rockers and until the LS no1 would have bought roller rockers w/o the tip also being roller. Many parts are based on what sells n not what is best for performance, thx to all the bigger is better folks. I read once a manufacturer engineer said roller tips were hot-rodder's pipe dreams. If you look at aftermarket stamped roller tip rockers, you'll see the rocker itself is much more HD than oem usually and that is part of the gain,(ie comp stamped roller tips), the next part is having more consistent ratio or just more ratio(advertised or not). I've also read of upper rpm lose with a ls engine that switch to roller tips and gained it back once retuning to non. I've seen pics of comp cams roller but normal tip rockers, idk if they are special order only or you gotta know someone but I emailed about them with no response awhile back. LOL maybe someone will eventually come out with non-roller tips you can buy or a kit to convert current roller tip sets and be like this is a high rpm only mod :) Or even lightweight roller tips.
Texas Speed has upgraded stock style LS rockers.

https://www.texas-speed.com/p-1088-texa ... ckage.aspx

Same exact OEM-style rockers are on my Vortec V6.
JC -

bigjoe1 wrote:By the way, I had a long talk with Harold(Brookshire) last year at the PRI show. We met at the airport and he told me everything he knew about everything.It was a nice visit. JOE SHERMAN RACING
User avatar
panic
Guru
Guru
Posts: 2295
Joined: Sat Dec 11, 2004 12:04 pm
Location: Ecbatana
Contact:

Re: roller rockers vs contact tip rockers

Post by panic »

The Trock (for Harley-Davidson iron Sportster, shovelhead, and Evo .557" shafts) rocker fixture shown depends entirely on operator skill to follow the existing pallet radius. You'll make an arrow head or a barn door if you're not careful. The Black & Decker, Kwik-Way, Rottler, Sioux, and Snap-On valve regrinding machines frequently have similar fixtures with adjustable conical pilots for different shaft diameters, but the same limitation: they have no fixture, pantograph, template, guide, etc. to restore the original pad radius, and no input the radius if you had that data.
hoffman900
HotPass
HotPass
Posts: 3445
Joined: Sat Feb 23, 2013 5:42 pm
Location:

Re: roller rockers vs contact tip rockers

Post by hoffman900 »

Here is the rocker ratio change over the duration of the valve lift curve from measured results for an application I deal with...

Image

More later...
-Bob
hoodeng
HotPass
HotPass
Posts: 1092
Joined: Sat Mar 04, 2017 6:53 pm
Location: South Australia

Re: roller rockers vs contact tip rockers

Post by hoodeng »

You are right Panic , one can make a terrible hash of a tired rocker if one is not vigilant to the vagaries of the Trock rocker tool!!! you can not trust the spring to give the required rolling resistance to the cut as it goes through its arc , i found that thumb pressure half on the jig base and half on the rocker at the end will control the cut and also skewing the rocker to the silicon carbide wheel instead of grinding at 90° will broaden the cut and slow it down .
This is probably the time to state that we have to start with parts that are readily retrievable and have a known record of service after re work to start with ,if you start with junk, rework it, you end up with shiny junk that i am sure will come back and leave nasty teeth marks on the buttock region.
There are a number of special tools here used to check the quality of re worked parts , but i would have to say the best quality check on any work is not seeing it again till many years later of satisfactory service, and finding what you have done previously not detrimental to a parts ability to perform adequately .
I have a Repco Syncro-Facer for my valve grinding machine [excellent tool] that came with all the special attachments ,the rocker facing tool was not designed for the Harley type rockers so i made one ,,after many years it is still corroding in the back of the cabinet waiting its chance to turn a good retrievable part into shit.


Cheers.
User avatar
panic
Guru
Guru
Posts: 2295
Joined: Sat Dec 11, 2004 12:04 pm
Location: Ecbatana
Contact:

Re: roller rockers vs contact tip rockers

Post by panic »

A warning: a common rumor, widely repeated, purports to answer the question: "what is the pallet radius?".
Answer: "It's the lift".
Not true, although it may be similar in common engines.
A 6" rocker lever with .500" lift moves through an arc of 2.4°.
A 2" rocker with the same lift needs 7.2°
Which one needs a larger pallet radius?
User avatar
MadBill
Guru
Guru
Posts: 15024
Joined: Tue Nov 15, 2005 10:41 am
Location: The Great White North

Re: roller rockers vs contact tip rockers

Post by MadBill »

A magic pad curvature would be geometry sensitive, e.g. if it was optimized for "90° @ 1/2 lift", it would be progressively less so if paired with a longer or shorter pushrod.
Also of course, the less the lift and the longer the lever, the less lateral motion to deal with, e.g. a Hemi exhaust rocker.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.
Post Reply