Rocker arm sweep across valve stem tip

[femtnmax]

I set up the rocker arm contact with the valve stem two different ways.  I like the second method better.
First setup had the rocker arm roller contacting the center of the valve stem.  With valve closed, the contact pattern started on the intake side of the valve centerline.  Then the contact swept across the centerline and stopped on the exhaust side of the centerline with valve full open.   Contact pattern width was 0.13 inch, valve lift was 0.523 inch.
For second setup, the rocker arm roller contact started a little to the exhaust side of the valve centerline with valve closed, the contact then moved a little further toward the exhaust side at mid valve lift, then the contact moved back toward the centerline at valve full open.  So the point of contact at valve closed and full open was the same.
Now the contact pattern width was only 0.08 inch  (a 38% decrease), and valve lift was 0.534 inch ( 0.011 inch increase, thats a 2.1% increase).  The rocker arm roller now rotates very little compared to the first setup, so side loading on the valve stem should be decreased an equal amount too.
Reading I've done said it's most important to have the rocker arm as perpendicular to the valve as possible (second setup), and not to worry if the contact pattern is not perfectly centered on the valve stem; although being centered and perpendicular would be ideal.
Phil

[Challenger340]

I think you'll get as many different preferences as you will answers.

IMO,
method # 2 is fine for all Flat Tappet & Hydraulic Roller stuff where Spring Pressurres generally stay lower on the Seat. The Trunion direction Change at Mid-Lift doesn't seem to matter much.

However,
if you are getting into "Race" Solid Roller Profiles, Cams requiring 210# Seat Pressures and "up", or even with the more aggressive higher RPM "mushier" stuff above, I'd definitely go for Method #1 to keep the Trunion Rotational Direction change away from the Mid-Lift, in favor of being ideally @ peak lift.

A Rocker Trunion Rotational Direction change "mid-lift", can set up goofy harmonics in the Valve Spring @ rpm, changing the Spring Slew Rate, and ability to maintain contact with the Cam profile.

Really, the change in direction at "mid-lift" is a STOP, then START back in the other direction, @ rpm,  at the quickest portion of the ramp. See where the Harmonic can happen ?

Just 1 opinion
Bob out.

[femtnmax]

Thanks Bob
Excellent response!!  Yours is the kiind of info I look for.  Now a couple of questions if its ok.

I'd definitely go for Method #1 to keep the Trunion Rotational Direction change away from the Mid-Lift, in favor of being ideally @ peak lift.

Are you suggesting to just ABOUT reach the point of rotational direction change at peak lift???   Then there would be NO CHANGE in direction; no induced harmonics.

Really, the change in direction at "mid-lift" is a STOP, then START back in the other direction, @ rpm,  at the quickest portion of the ramp. See where the Harmonic can happen ?

I absolutely see what your saying about inducing harmonics.   
Would "your" method be applicable to solid flat tappet cams with spring seat pressures above say 140-150 Lbs???
Thanks.  Phil

[Challenger340]

Fine by me, these are just my opinions, "always more than 1 way to skin a cat".

Yeah, thats what I typically shoot for, is to get the Trunion to change direction as close to peak lift as possible, but I get more persnickity about it, the more agressive the Cam/Spring Rate.

Like you said; Start on the Intake side of the Tip, propagate across the Tip to the Exhaust side @ Peak, Change direction, then go back.
That said,
I've also seen lots of mid spring Rate/Pressure stuff run just fine, having a directional change @ mid-lift.


Again, just my 2 cents, and I'm nobody !
yes, I prefer the "no Change @ mid-lift" method, for Flat Tappet Cams requiring 140-150 lb Seat Pressure, especially with todays cheesey Rocker parts out there. I think thats why the 440source rocker trunions fall so miserably !  Dir-change @ mid-lift, Trunion wiggles out, MAD Customers.

At the 140-150Lb Seat Pressure mark, it sounds like you are getting into some of the more Agressive .904" tappet stuff ?
Hughes ?
Schnieder ?
What's the Valve Spring Rate for the above Seat Pressure ?
Your not getting approaching 400# are you ?

Bob out.

[firefighter3931]

Good discussion about something that often gets overlooked 

From my experience the higher ratio stuff tends to create more problems. Some rocker arms are a good fit while others create issues. I've had good luck with Crane and Harland Sharp. With flat tappet spring pressures my primary concern is the valve tip at full lift. Ideally the roller needs to be as close to center as possible with a descent sweep pattern that doesn't come near the edge at any point in the lift cycle. 

In the past i've used a set of lash caps to  compensate for a mediocre pattern but that was on a hydraulic cam profile that wasn't running on the ragged edge in terms of lobe velocity. It worked fine with no adverse effects. 


My next build will be using a Solid Roller with HS 1.5's and a set of Indy heads so i'll be paying closer attention when looking over the valvetrain geometry. The cam profile is more of an endurance/high rpm lobe to help it live on the street. Also going to try a set of the Isky Red Zone roller lifters with the EZ-Roll option that uses a solid bushing in place of the needle bearings.



Ron

[Challenger340]

Your Right on Ron, in that Rocker Geometry is a too-often overlooked aspect of Building ?

I mentioned this before, and I'll mention it again here now;

I've got "Crane Gold's" out there, surviving just fine under 250 lb Seat Pressures on Race Roller profiles at the Drag Strip with no problems.

NOT, my first choice for a Rocker in THAT application,
But,
Hard to argue with the Customer, when he comes back for freshening after 300-400 pulls, and the "Golds" are just fine ?

We usually cycle them out in favor of new ones anyways, re-use our homebuilt Rocker spacers,
But,
for the price, VERY hard to convince a guy to "upgrade", if you know what I mean here ?

THANK GOD Crane went out of Business, NOW, they'll have to upgrade and I'll sleep better !