roller rockers vs contact tip rockers

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
Geoff2
Expert
Expert
Posts: 950
Joined: Mon Nov 09, 2015 4:36 pm
Location: Australia

Re: roller rockers vs contact tip rockers

Post by Geoff2 » Sat Dec 09, 2017 4:35 am

CJ,
It is incorrect to say a stock rocker rolls with no sliding action across the [ valve ] tip. On a well used rocker, you will see the wear mark, often 1/8" to 1/4" wide. Since the pad on the rocker is part of an arc of a circle [ & therefore curved ] it would make a very narrow wear mark [ point contact ] on the rocker pad, only if the rocker did NOT slide; but it does slide, hence the wide wear pattern.

P. Kane,
Once again you either didn't read what I said or you misread it. Nowhere did I say that the T to roller tip was the only part of the equation to affect rocker ratio. I specifically said the p'rod side dimension is the other part of the rocker ratio & gave actual numbers as an example, 1.5", 1" for a nominal 1.5 ratio!! The fact is that the dimensions that provide the operating rocker ratio can & does vary through the sweep of the rocker. As an example, a nominal 1.5 ratio rocker might provide an operating or true ratio of 1.45 to 1.6 from valve open to valve close. At some point [ or points ] during the ratio might actually be 1.5.
There is no better example of the variables than the tests done by D. Vizard on rocker ratios, examples given in his BBC book. Two 1.7 alum rockers have the same 0.123" lift @ TDC, but one has 0.607" at full lift, the other 0.623". Another example, s/s 1.7 rockers. Two were very close in lift @ TDC, 0.125" & 0.126", but had 0.619" & 0.601" at max lift; note that the the rocker that had less lift @ TDC had more lift at max lift. It shows the variables involved & the way that the rocker ratio changes, from opening the valve to max lift & closing again.

Incidentally, if you read the original post by the OP, he started out by asking about friction differences, but finished his post asking about differences between roller & FT cams. So not just about friction....

Geoff2
Expert
Expert
Posts: 950
Joined: Mon Nov 09, 2015 4:36 pm
Location: Australia

Re: roller rockers vs contact tip rockers

Post by Geoff2 » Sat Dec 09, 2017 4:53 am

Just to add some more examples of varying rocker ratios, through out the lift cycle.

Here is an example of same lift at TDC, but more lift at max lift. 1.7 alum rockers: 0.123"/0.607"; 0.122"/0.613".

Here is an example of same lift at TDC, less lift at max lift. 1.8 rockers: 0.126"/0.649"; 0.127"/ 0.638"

digger
Guru
Guru
Posts: 1319
Joined: Sun Jan 27, 2008 6:39 am

Re: roller rockers vs contact tip rockers

Post by digger » Sat Dec 09, 2017 4:56 am

Not enough people plot out valve lift profiles, it's one thing to check some opening and closing points or centrelines but if you want to understand performance and effect of different parts you need to see and compare the whole curve.

Vincenzo
New Member
New Member
Posts: 42
Joined: Tue May 28, 2013 4:11 pm

Re: roller rockers vs contact tip rockers

Post by Vincenzo » Sat Dec 09, 2017 7:23 am

HeinzE

your interest is in a motorcycle, and for such an application you need to keep in mind one very important aspect - a roller ended rocker arm will bring with it unacceptable weight just where it's not needed, on the valve side of the rocker pivot.
For your Aermacchi you are far better to stay with the stock rockers, but if you take a page out of BILL-C's notebook and re profile the pad, you can further improve the contact.
For those who have access to Prof. Blair's software 4StHead, this reprofiling is described and calculated under sub program #7.

Re plotting the valve lift profiles, be aware that the profiles measured from a non running engine will differ when the engine is running, with the biggest difference being in a delay (lag) of the exhaust valve opening as compared to the static measured. and can with a pushrod engine in extreme cases be as much as 20 crankshaft degrees

twl
Expert
Expert
Posts: 652
Joined: Thu Feb 21, 2013 11:13 am

Re: roller rockers vs contact tip rockers

Post by twl » Sat Dec 09, 2017 9:11 am

exhaustgases wrote:
Fri Dec 08, 2017 6:45 pm
Its pretty much simple trigonometry, a the end of the rocker tip on the stem has a wipe,,,wiping motion across the contact area. And for argument if a non roller rocker had high contact pressure and no lubrication that motion is transferred into side loading the valve stem.
To add to that, the oil film is the least effective possible in that location because there is nothing to stop the oil from squishing out under the loading and movement.

I would also add that I have never seen a factory rocker that even came close to behaving like some have described as their theoretical behavior in real life.

Regarding the roller mass at the end of the rocker, what other material that's lighter is going to be at the end of that rocker? It's going to be steel or iron anyway. That argument is moot, especially in a pushrod engine that has typical pushrod rpm limitations.

I would also add that it is virtually assured that nearly all of us here are running roller rockers in our own vehicles, if available.

As I previously mentioned, the roller could be better if it rolls, but won't be worse even if it doesn't .

All IMHO, of course. :D

I run a pushrod motorcycle application fairly similar to Heinz, as shown earlier in this thread, and my T&D roller rockers are working admirably in the performance application.

hoffman900
Guru
Guru
Posts: 1722
Joined: Sat Feb 23, 2013 5:42 pm

Re: roller rockers vs contact tip rockers

Post by hoffman900 » Sat Dec 09, 2017 10:26 am

NASCAR circa the mid-late 2000s (TRD and Ford) were using rockers with no roller. They were either steel rockers with DLC coating or aluminum on the radius pad. Not sure if they're still used. Warp can comment.

Modern finger follower systems don't use rollers on the valve side, and DLC is common in those applications.

https://www.ebay.com/itm/Del-West-Chevy ... 2206655309

Image
Image
-Bob

plovett
Expert
Expert
Posts: 660
Joined: Sat Dec 30, 2006 3:49 pm
Location: Kansas City

Re: roller rockers vs contact tip rockers

Post by plovett » Sat Dec 09, 2017 2:43 pm

I don't see how it is possible to have no sliding between a non-roller tip rocker and the valve stem. The angle between the two has to change as the valve moves. If the angle changes, there has to be a sliding motion, no? Maybe the area on the valve stem that this occurs on is very small, but metal sliding across metal still has to happen. Am I missing something?

paulie

twl
Expert
Expert
Posts: 652
Joined: Thu Feb 21, 2013 11:13 am

Re: roller rockers vs contact tip rockers

Post by twl » Sat Dec 09, 2017 3:03 pm

Bob,
It appears that there is some kind of pad under that rocker wiper. Probably the reason being that the A-beam design of that rocker doesn't lend itself to a forked tip to support a roller, so they used a pad to avoid the weight increase of a forked tip. My conjecture, of course, but it would seem to have some basis considering that rocker construction.

In that scenario, it is very reasonable to skip the roller, in keeping with the selected rocker design. An H-beam rocker intended for a more streetable rpm range would be just as well suited with a less exotic and less expensive roller tip without mass concerns for the rpm range.

IMO.

hoffman900
Guru
Guru
Posts: 1722
Joined: Sat Feb 23, 2013 5:42 pm

Re: roller rockers vs contact tip rockers

Post by hoffman900 » Sat Dec 09, 2017 3:17 pm

Tom,

What I could find on the steel version of those that TRD used is they reduce MOI by up to 90% and a 60% increase in stiffness. I’m not sure if they’re still used however.

Also, keep in mind that NASCAR engines keep the valve covers flooded with oil.
-Bob

twl
Expert
Expert
Posts: 652
Joined: Thu Feb 21, 2013 11:13 am

Re: roller rockers vs contact tip rockers

Post by twl » Sat Dec 09, 2017 3:43 pm

hoffman900 wrote:
Sat Dec 09, 2017 3:17 pm
Tom,

What I could find on the steel version of those that TRD used is they reduce MOI by up to 90% and a 60% increase in stiffness. I’m not sure if they’re still used however.

Also, keep in mind that NASCAR engines keep the valve covers flooded with oil.
Yes, understood.
My main point being that an item for a cost-no-object 11k rpm highly specialized application is not necessarily the best choice for a 6500 rpm cost sensitive hotrodder application.

Getting back to the roller rocker vs plain tip rockers, I had to make the decision for my application and I couldn't come up with any reason to not have the roller tips, so I got them. I still don't see any downside to having them in my application. If I needed 11k rpm, I would have designed an OHC head instead.

hoffman900
Guru
Guru
Posts: 1722
Joined: Sat Feb 23, 2013 5:42 pm

Re: roller rockers vs contact tip rockers

Post by hoffman900 » Sat Dec 09, 2017 3:58 pm

twl wrote:
Sat Dec 09, 2017 3:43 pm
hoffman900 wrote:
Sat Dec 09, 2017 3:17 pm
Tom,

What I could find on the steel version of those that TRD used is they reduce MOI by up to 90% and a 60% increase in stiffness. I’m not sure if they’re still used however.

Also, keep in mind that NASCAR engines keep the valve covers flooded with oil.
Yes, understood.
My main point being that an item for a cost-no-object 11k rpm highly specialized application is not necessarily the best choice for a 6500 rpm cost sensitive hotrodder application.

Getting back to the roller rocker vs plain tip rockers, I had to make the decision for my application and I couldn't come up with any reason to not have the roller tips, so I got them. I still don't see any downside to having them in my application. If I needed 11k rpm, I would have designed an OHC head instead.
Of course. I think your set-up is awesome, btw. What application are those T&D, billet head rockers off of?
-Bob

BILL-C
Pro
Pro
Posts: 363
Joined: Thu Feb 07, 2008 9:57 pm
Location: Oakville, CT
Contact:

Re: roller rockers vs contact tip rockers

Post by BILL-C » Sat Dec 09, 2017 4:13 pm

plovett wrote:
Sat Dec 09, 2017 2:43 pm
I don't see how it is possible to have no sliding between a non-roller tip rocker and the valve stem. The angle between the two has to change as the valve moves. If the angle changes, there has to be a sliding motion, no? Maybe the area on the valve stem that this occurs on is very small, but metal sliding across metal still has to happen. Am I missing something?

paulie
The key is the shape of the rocker tip. When the arc is correct, the rocker tip will walk across the valve tip without skidding or scrubbing.A very smart older engine builder [ T.O.] turned me on to this. In the "bad old days" there were no roller rockers, and the stock rockers were often the weak link. He figured out how to make them work better than most others and accidently pointed me in the right direction.
Carlquist Competition Engines

twl
Expert
Expert
Posts: 652
Joined: Thu Feb 21, 2013 11:13 am

Re: roller rockers vs contact tip rockers

Post by twl » Sat Dec 09, 2017 5:10 pm

hoffman900 wrote:
Sat Dec 09, 2017 3:58 pm
twl wrote:
Sat Dec 09, 2017 3:43 pm
hoffman900 wrote:
Sat Dec 09, 2017 3:17 pm
Tom,

What I could find on the steel version of those that TRD used is they reduce MOI by up to 90% and a 60% increase in stiffness. I’m not sure if they’re still used however.

Also, keep in mind that NASCAR engines keep the valve covers flooded with oil.
Yes, understood.
My main point being that an item for a cost-no-object 11k rpm highly specialized application is not necessarily the best choice for a 6500 rpm cost sensitive hotrodder application.

Getting back to the roller rocker vs plain tip rockers, I had to make the decision for my application and I couldn't come up with any reason to not have the roller tips, so I got them. I still don't see any downside to having them in my application. If I needed 11k rpm, I would have designed an OHC head instead.
Of course. I think your set-up is awesome, btw. What application are those T&D, billet head rockers off of?
Bob,
They are BBC 1.8:1 ratio and they are modified with an angled adjuster to provide better angle of incidence with the angled pushrods . We do use the pushrod oiling with this head, which was absent in the stock block-style offset rockers with plain tips. Hydraulic roller tappets too. So far, no failures or issues reported up to 10k miles of the ones on the road. If we get 50k miles between rebuilds, we'll be happy. Time will tell.

Geoff2
Expert
Expert
Posts: 950
Joined: Mon Nov 09, 2015 4:36 pm
Location: Australia

Re: roller rockers vs contact tip rockers

Post by Geoff2 » Sun Dec 10, 2017 3:31 am

hoffman900,
That Nascar style rocker you showed is a refinement of the type of rocker Chrysler used in 1956, with the intro of the Poly head. Shaft mounted, with a pad instead of a roller tip.

Geoff2
Expert
Expert
Posts: 950
Joined: Mon Nov 09, 2015 4:36 pm
Location: Australia

Re: roller rockers vs contact tip rockers

Post by Geoff2 » Sun Dec 10, 2017 3:37 am

plovett,
Your thoughts & comments are 100% correct about the movement of the rocker tip across the valve. Both the angle of contact of the rocker tip with the valve tip, AND the distance between the rocker pivot [ trunnion or ball ] to the contact point on the valve tip change as the rocker opens & closes the valve. Result is some amount of sliding action of the rocker tip.

Post Reply