My rocker is confusing me

Thought I'd poise on that.

Well it looks like it's marked as an EAN which is 1.43
Yet it's got numbers 6564
However being the head and deck have had about .100" taken off them the adjuster is pretty much in the middle of its adjustment.
This makes the valve arm 1.5360" from the centre axis. Now this is how I interpret the pushrod arm axis, to the centre of the ball. And it's length is .8660"
So when I divide 1.5360 x .8660 I get 1.774:1 ratio
What am I doing wrong?

I cannot help with your math but for what it's worth, the 6564 is merely the base catalog part number for all rockers. The EAN tells you which of the 6564 rockers it is.



Tom from the chiggerfarm located in the beautiful Heart of Central Texas

When you cannot dazzle others with your brilliance, baffle them with bullcorn!

You can't know precisely how it contacts the valve and pushrod and I imagine that is where the error is coming from.  The correct way to check is  to measure pushrod movement and valve movement and use those figures to determine the ratio.  This probably won't return the published ratios either but it will tell you what the rocker ratio actually is.



Lawrenceville, GA

I'm not sure about the math involved either. However, those rockers are 1:43 nominal ratio. John Mummert wrote a blurb on this subject,quite some time ago in Y-Block magazine, but I doubt I can find it now. Maybe someone out there remembers?.. 


Paul

I could be way off and this could be a stupid comment, but I always understood the ratio of the rocker to be the differential of the imput-pushrods for how far it pushes down across the fulcrum on the valve. So the pushrod pushes up 1 unit and pushes down 1.49.

From my understanding from what you are describing with the lowered deck you have changed the lift of the pushrod (in essence lengthened the pushrod with a shorter deck)
It would be more akin to a different lift or larger lobe on a cam swap.

I don't think it would change the rocker ratio, but might affect the overall lift or increase the opening of the valves.

Or that is a guess and I am a noob-either would be accurate, and I will defer to one of the guru engine builders.

Mike Rizzo

1963 F100 "Rudy"

Daniel Island, SC

Riz, you are correct.  The position of the adjuster screw does affect the ratio.  All the way in is a lower ratio.  All the way out is a higher ratio.  So everything else the same, milled heads or block will result in a higher ratio which affects the lift and duration at the valve..But that's not what is going on here since it is only the rocker itself being measured.



Lawrenceville, GA

Perhaps it's actually the point of the ball at which the leverage is actuated. Or that the valve and pushrods are angled differently 16* and with the shaft positioning, the geometry is altered in some way.
I have now turned the engine with a dial indicator at the valve and I'm getting .420" which is what a 1.43:1 rocker would do being the cam has a lift of .293"
Has any one got one of each to sit side by side?

Here is a picture.  1.54:1 above 1.43:1 below.  You can see that the ball on the adjuster screw for the 1.54 is much closer to the rocker body than the 1.43.  You can use a drill bit to measure the gap.  1/4" for the 1.54 and 11/32" for the 1.43.  If the 11/32" bit won't fit its a 1.54:1 rocker.


Mark

1956 Mercury M100
1955 Ford Fairlane Club Sedan
Delta, British Columbia

I measured the rocker again, yet this time at the tip of the ball and this gives a ratio of 1.43:1.

Thanks for the help guys.

Hey guys.
If you haven't read it you should.

http://www.enginebuildermag.com/2009/11/performance-rocker-arm-shaft-systems-time-tested-technology-provides-proven-performance/