Too much lift?!?!?

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redliner
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Too much lift?!?!?

Post by redliner » Fri Jan 19, 2018 8:26 pm

I have a Jones solid roller. It sports a .421 lobe and I am using a 1.7 rocker for a gross lift of .7157. I did a preliminary check tonight and it looks like .729 lift ( at the retainer with light spring). I have an adjustable p-rod in it and followed T&D rocker system directions for determining p-rod length and I think I have it correct. My question is how can I have .729 when it should be .7157???

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Re: Too much lift?!?!?

Post by Walter R. Malik » Fri Jan 19, 2018 8:33 pm

redliner wrote:
Fri Jan 19, 2018 8:26 pm
I have a Jones solid roller. It sports a .421 lobe and I am using a 1.7 rocker for a gross lift of .7157. I did a preliminary check tonight and it looks like .729 lift ( at the retainer with light spring). I have an adjustable p-rod in it and followed T&D rocker system directions for determining p-rod length and I think I have it correct. My question is how can I have .729 when it should be .7157???
Measure LOBE lift at the lifter not AFTER the rocker arm.
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Re: Too much lift?!?!?

Post by redliner » Fri Jan 19, 2018 8:39 pm

Walter R. Malik wrote:
Fri Jan 19, 2018 8:33 pm
redliner wrote:
Fri Jan 19, 2018 8:26 pm
I have a Jones solid roller. It sports a .421 lobe and I am using a 1.7 rocker for a gross lift of .7157. I did a preliminary check tonight and it looks like .729 lift ( at the retainer with light spring). I have an adjustable p-rod in it and followed T&D rocker system directions for determining p-rod length and I think I have it correct. My question is how can I have .729 when it should be .7157???
Measure LOBE lift at the lifter not AFTER the rocker arm.
I am trying to check gross lift at the retainer

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Re: Too much lift?!?!?

Post by Baprace » Fri Jan 19, 2018 8:48 pm

It's hard for me to explain, but if you study the pushrod seat center distance from the pivot center of the rocker you will notice the more you open or close the rocker the pushrod seat will get closer to the center pivot and the closer to the pivot you get , you are actualy changing the rocker ratio, I think that is why the max lift is sometimes referred to as theoretical valve lift. I know what I am trying to explain but I'm not sure if I explained correctly. You may try making a rocker arm with a popsicle stick and a pin going thru to similate the fulcrum and now that you have a fulcrum measure the distance to a pushrod seat and move the pushrod seat up or down and you will see the pushrod center distance from pivot center will get closer to the fulcrum.

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Re: Too much lift?!?!?

Post by Rick360 » Fri Jan 19, 2018 8:50 pm

Rocker arms are never exactly the ratio indicated and no way they can be. As the pushrod length changes the geometry changes the ratio and you'll have different lift. It is different ratio early in the lift vs late in the lift. Too many variables for an exact number.

Put the real springs on it and measure lift again and you'll likely see .020" gone.

What you see is normal.

Rick

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Re: Too much lift?!?!?

Post by MadBill » Fri Jan 19, 2018 10:53 pm

This. Manufacturers often build in a little more ratio than they advertise, to ensure that with the inevitable deflection under full spring force, the expected lift still results.
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Re: Too much lift?!?!?

Post by steve cowan » Fri Jan 19, 2018 10:54 pm

Yep,
Seen same as rick a few times before
Done a flat tappet cam few weeks ago
Intake spec 555 lift with 1.6 rocker
Check with lite spring had 570 lift I thought great got some free lift,
Nope
Fit valve springs and check it out at 550"
Lift,
Imagine what happens when engine is running and we have valve train deflection
OOPS JUST OPENED UP A CAN OF WORMS

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Re: Too much lift?!?!?

Post by steve cowan » Fri Jan 19, 2018 10:56 pm

Sorry bill,
I was writing my post same time as you
Didn't want to steal your thunder
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Re: Too much lift?!?!?

Post by MadBill » Fri Jan 19, 2018 10:58 pm

No sweat Steve, I got more.. =P~
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: Too much lift?!?!?

Post by nitro2 » Fri Jan 19, 2018 11:13 pm

MadBill wrote:
Fri Jan 19, 2018 10:58 pm
No sweat Steve, I got more.. =P~

:)
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Re: Too much lift?!?!?

Post by tresi » Sat Jan 20, 2018 12:00 am

Is you dial indicator completely parallel to the valve stem in each axis. Any more than a little deviation from 90* will induce a co sign error in your dial indicator reading.

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Re: Too much lift?!?!?

Post by andyf » Sat Jan 20, 2018 12:32 am

Check it with a real spring and you'll have less than 0.715. Then you can start another thread saying you don't have as much lift as you expected...........
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Re: Too much lift?!?!?

Post by af2 » Sat Jan 20, 2018 12:57 am

andyf wrote:
Sat Jan 20, 2018 12:32 am
Check it with a real spring and you'll have less than 0.715. Then you can start another thread saying you don't have as much lift as you expected...........
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Re: Too much lift?!?!?

Post by Krooser » Sat Jan 20, 2018 1:04 am

Mike has a "lift" sale every few years... get .730" of valve lift for the price of .715"!!! :mrgreen:
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Re: Too much lift?!?!?

Post by Geoff2 » Sat Jan 20, 2018 3:57 am

Many variables with rocker arm geometry, such as position of the prod cup [ up or down ] relative to the trunnion. These variations affect final valve lift.
David Vizard tested some '1.7' rockers, different brands, & valve lift varied from 0.550" to 0.636"!!

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