Too much lift?!?!?

[CamKing]

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???

The mechanical ration of a T&D 1.7 rocker is actually 1.75. They are trying to correct for deflection.. If you put the heavy springs on, the lift will come down.

[CharlieB53]

Unfortunately the both ends of all rockers travel in an ARC relative to the fulcrum.

While the distance from the pivot remains the same lift relative to that fulcrum suffers the same as piston speed changes during stroke reaching max speed at mid travel but total distance/lift will remain limited by the camshaft lobe.

Measuring pushrod length so as to ensure mid-lift the rocker is 90 degrees to the pivot, equalizing that travel arc before/after that 90 degree mid-lift position. can be a trick.

[redliner]

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???

The mechanical ration of a T&D 1.7 rocker is actually 1.75. They are trying to correct for deflection.. If you put the heavy springs on, the lift will come down.

I wondered that! I thought T&D figured in deflection. Thanks to all who answered!

[midnightbluS10]

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.

Edit: nevermind. Did some reading and see that I need to learn more. Sorry! Feel free to delete.



Thanks to Harold, still educating automotive enthusiasts in 2018.

I'm UDHarold.......

Everyone is correct. Because of pushrod angularity, the valve only gets the Cosine of the lobe lift, which is varying as the lobe turns, but should always be above .975, or thereabouts....... Only OHC engines with direct-acting cam lobes deliver true lobe lift.
Pushrod deflection is also into play, and everyone should use the stiffest pushrod they can. On the cam side of the rocker arm, stiffest is most important. On the valve side of the rocker arm, lightest pays off a lot. This is why we have the return of the BeeHive spring---It lightens the valve side of the equation, a lot.
Angularity is a fact of life in engines, and the higher the lobe lift, the more angularity. Remember, the valve movement in the 75* ATDC is really more important than a few more thousands of valve lift. The conditions for good intake port flow are set up in those first 75*, not around max valve lift.

UDHarold

From viewtopic.php?f=1&t=4679

[turdwilly]

The mechanical ration of a T&D 1.7 rocker is actually 1.75. They are trying to correct for deflection.. If you put the heavy springs on, the lift will come down.

Jesel are the same. Put 1.7 Sportsman series on a SBF, with a .3973" lobe & checking spring had .699" at the retainer with zero lash. With 625# open springs & .015" cold lash had .665" at the retainer.