roller rockers vs contact tip rockers

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HeinzE
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roller rockers vs contact tip rockers

Post by HeinzE » Tue Dec 05, 2017 1:11 pm

I've been wondering a bit about the actual advantages of roller rockers vs the std contact tip style. I work almost exclusively with motorcycle engines and have fairly limited experience with roller rockers, except for having installed a dozen or so sets in Harley-Davidson engines. Many modern motorcycle engines rev over 14,000rpm and most run the cam lobe directly on a tappet or shim on a tappet. Hard to imagine more "contact" than that.
All the early Honda multi cylinder engines used a radiused threaded adjuster that made direct contact with the valve tip, and although these engines were not without problems, the top end was not one of them. In reading through engine building books and magazines and performance blogs it seems that roller rockers are considered almost a manditory "upgrade", with claims of more power and lower oil temperature often claimed. 20hp increase and 10deg drop in oil temp or in that range are numbers often stated, regardless of engine size or rpm pk, which seems a bit formulaic and that folks are just repeating things thev'e been told or read in advertisements. The roller rides on an axle and doesn't actually roll but ocillates, so there has to be "friction" between it and the axle, no? Is that friction less than that at a radius contact tip? which if all things are as they should be is sliding on a film of oil. Also, if putting a roller on a rocker tip makes that kind of difference, why not put one on the pushrod side too? The loads on that side are higher so the gains should be even more. But no one seems to worry about that. 4stroke motorcycle crankshafts used to be almost universally roller or needle bearing at the big end but are now just about all insert bearing style; the major players having found that rolling element big ends gave no definitive advantage in either power or reliability and certainly not in lower oil temps. Like I said, my experience with roller rockers is limited to a handful of Harley engines, but in those I couldn't feel or measure any differences. Maybe in an 8 cyl. or more engine they do make a difference, but in a twin or single? To relate this to another part of an engine - the lifters - we all understand that roller tappets can make more power than a flat tappet, or at least should. But isn't that because the cam lobe can be more aggressive and give more area under the curve? If a roller cam gave the identical valve motion as a flat tappet would it still make more power because of the rollers? Anyway, as I said, my experience with roller tappets is limited and I'm not arguing one side or the other. Just honestly curious.

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Re: roller rockers vs contact tip rockers

Post by pamotorman » Tue Dec 05, 2017 1:24 pm

the friction must be in the fulcrum as the GM LS engine still uses a sliding foot on the valve tip but uses a needle bearing in the fulcrum

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Re: roller rockers vs contact tip rockers

Post by lefty o » Tue Dec 05, 2017 1:51 pm

everything ive ever seen has shown the roller tips benefits to be insignifigant.

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Re: roller rockers vs contact tip rockers

Post by F-BIRD'88 » Tue Dec 05, 2017 2:04 pm

The roller tip adds a more heavy er mass right where you don't want it.

The roller bearing fulcrum is in the center of the pivoting rocker. Mass at the outer ends is more critical.

Crane had some coolroller rockers with a small hard radius pad tip.... Did not sell well against pretty sexy "roller" bling.

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Re: roller rockers vs contact tip rockers

Post by Frankshaft » Tue Dec 05, 2017 2:19 pm

Something to think about. Needle bearing roller tipped jesel rockers. Spit one apart every 30 or so passes. Random rockers. Jesel says, no needle roller tips for over x amount of open spring pressure. Switch rockers, no needle bearings in roller tips. Never an issue again. I should clarify, it would ruin a roller tip. Needle bearings would lock up. It would then flat spot roller tip, and cause lash to move. Lash caps saved valve tips.

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Re: roller rockers vs contact tip rockers

Post by PackardV8 » Tue Dec 05, 2017 2:58 pm

pamotorman wrote:
Tue Dec 05, 2017 1:24 pm
the friction must be in the fulcrum as the GM LS engine still uses a sliding foot on the valve tip but uses a needle bearing in the fulcrum
From what I've read, prior to and ongoing LS development, GM extensive, detailed research and found very little benefit to roller tips and very likely warranty problems. Even their highest performance engines, with titanium valves and titanium connecting rods, still use sliding tips; for true?
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Re: roller rockers vs contact tip rockers

Post by Casper393W » Tue Dec 05, 2017 3:18 pm

The new episode of Engine masters covers this very topic. They ran a 500hp engine with stamped rockers, roller tip stamped rockers, Roller rockers, and 1.6 Roller rockers. The results was eye opening!

Andy

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Re: roller rockers vs contact tip rockers

Post by digger » Tue Dec 05, 2017 3:33 pm

Latest engine masters tests roller rockers

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Re: roller rockers vs contact tip rockers

Post by turbo2256b » Tue Dec 05, 2017 3:45 pm

Test Ford did roller tip helped from idle to just off idle range and required a more exact valve tip contact. Slipper tips friction just past idle was insignificant about the same as roller tip but valve tip contact was more forgiving. Biggest difference in friction was the fulcrum needle bearing had as much as a 25* difference in temp over the ball or barrel style.

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Re: roller rockers vs contact tip rockers

Post by BOOT » 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.
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Re: roller rockers vs contact tip rockers

Post by Zmechanic » Tue Dec 05, 2017 4:14 pm

digger wrote:
Tue Dec 05, 2017 3:33 pm
Latest engine masters tests roller rockers
Yup. And in their test switching to 1.5 roller rockers lost in the upper RPM vs very good stamped steel howards units w/balls. Roller tip, stamped steel rockers were the worst, but they were also the only ones that used 3/8" studs, so not apples-apples.

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Re: roller rockers vs contact tip rockers

Post by strokersix » Tue Dec 05, 2017 4:57 pm

Seems to me the valve action would be different due to geometry effects between a large contact radius stock stamped and roller tip. True or no?

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Re: roller rockers vs contact tip rockers

Post by hoodeng » Tue Dec 05, 2017 6:34 pm

I have been reconditioning the v twin engine for many years now , and some customers over those years insisted on roller rockers , and i would say honestly that i have seen no advantage . There are early models of the v twin engine that suffered from stem to rocker scuffing but those same engines would present rocker pushrod bucket scuffing as well in some cases ,this indicates a lubrication [storage] issue and not a loading issue .By nature of the products sometimes seasonal use and sometimes extended storage cycles the incidence of a dry start up is increased ,compounded by engines not being stored with a pre storage oil change. I am amazed at the person who will pull a bike from a shed unused for who knows how many years, kick over,drag down the road , hook up battery's and generally force the thing into life ,not realizing the damage they are doing ,, i would strip the top end at least and make sure the bottom end has been drowned in oil before trying to get dads old bike going again.... Maybe i shouldn't say too much , as repairing them provides me with constant stream of work!
Since the evo engine {which due to its age now can show stem damage} the incidence of scuff has diminished greatly to the point the later 7mm valves with .625" lift very rarely scuff , i set all of these at 180lb seated for street use and have no issue.
I have found in some engines with roller rockers after extended use, the incidence of trenching of the stem at the path of the roller ,i would say also that its incidence also coincided with the use of one brand of valve that was used in a kit combination.
There is more likelihood of stem and rocker tip damage coming from inadequate seated pressure of the valve , i have seen a number of heads that have come from engines that have had bolt in performance cams with the standard springs retained having tip damage ,the damage is usually spalling caused by the rocker slapping against the stem ,there can be the same damage on the corresponding rocker face. the cams installed in these engine allow the engine to continue to produce torque into the upper rev ranges where the stock cam would have nosed over, so the tendency to give the throttle a bit of free range becomes more likely .
A rigid lubricant at assembly will ensure adequate lube on startup.

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Re: roller rockers vs contact tip rockers

Post by kirkwoodken » Wed Dec 06, 2017 1:49 am

Does anyone still make roller rockers with paddle ends? I used some Thompson's back in the 60's and liked them. Unlike the roller tip, the sliding tip increases ratio as the valve opens. The roller tip increases ratio slightly during the first half of lift, but the paddle tip increases ratio through the entire lift. Just look at the valve wear pattern on a stock stamped rocker! It's not a .040" thin line.
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Re: roller rockers vs contact tip rockers

Post by hoffman900 » Wed Dec 06, 2017 2:28 am

I can’t think of any high rpm Japanese / Euro engines wth roller tipped rockers. I’m surprised the NASCAR guys still use them to be honest. Would like to know what they’ve found. Warp?
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