I have tried the eo/ic method and also used the pushrod length checker tool and compared the number to make sure I was doing it correct and this is what I came up with:

my set up is tis 215 59cc, mls gasket, ls7 lifters, stock rockers with trunion upgrade.

using the pushrod length checker 0 lash is at 11.5 turns= 7.375 + .075 preload should put me at 7.450. So to double check my results I tried the eo/ic method and this is what I came up with

eo/ic using 7.400 I was able to get 3/4 turn, so I added a 7.450 (pushrod length checker opened to that measurement) which per calculations should have put me at 1 3/4 turns, but am only able to get 1 3/8 turn. why?

am I doing something wrong or over looking something? which measurement should I go with? 7.450 pr length checker or go up to the 7.475 with the eo/ic ?

If you have a similar setup what size did you use? Thanks

 

If using stock rockers, you should be able to just torque to 22 ft/lbs, measure length to zero lash, add preload and go.

 

If you are using the rocker bolt turns method then I calculate like this: The bolt thread pitch for one turn = .049. Don't forget the rocker ratio 1.7. Now even deeper the factory 1.7 rocker arm actually leaves the seat @ 1.54. So 1 full turn of the rocker bolt is .049 but you have to multiply that by 1.54 to get the correct measurement. (1 turn .049) X (rocker arm ratio 1.54) = .07546 preload. I have confirmed this with a pushrod length checker as well.

 

Poltergiest, so if i understand correctly 1 turn with stock rockers equals .075 preload, not .049? Thanks

 

yes but that is not torqued to 22ft lbs though. It would be 1 full turn to snug to eliminate the bolt stretch variable. Most likely you pushrod checker is correct.

 

Forget the turns to 22fts! Trust your method of measuring with the tool. There are variables which makes the "turns to torque" for pre-load in-valid. Such as calibration of the torque wrench and bolt stretch. I personally dis-like when people talk about this method. Its just guesstimate.

 

There are two corrections you have to make when you do this. First, when you tighten down the rocker bolt the rocker bottoms in the stand before the bolt hits the torque value. I found this extra bolt rotation after the rocker bottoms to be about 1/3 turn (0.333 turns). This last 1/3 turn is not preloading the lifter much but rather stretching the bolt. So this must be subtracted from your counted turns as it doesn't contribute to rocker movement or preload.

Next, you must correct for rocker ratio. Since the rocker pivots about the valve stem you have two parallel triangles that are used to get the preload since movement at the pushrod is greater than movement at the bolt as you tighten and the rocker pivots about the valve stem. So for your first case, with 3/4 turn here is what I get:

(0.75 turns - 0.333 turns) = 0.417 turns

Now convert to movement:

0.417 turns X 1.25 mm/turn = 0.52125 mm of bolt movement

0.52125 mm / 25.4 inches per mm = 0.0205 inches of bolt movement

Now correct for rocker ratio where the ratio from the valve stem is 2.54 (to pushrod cup) to 1.54 (to the bolt) you get the following for preload:

0.0205 X 2.54/1.54 = 0.034" of preload

Using your second measurement of 1-3/8 turns you get a new preload of:

(1.375-0.333) X (1.25/25.4) X (2.54/1.54) = 0.085" of preload or approximately 0.050" difference per your pushrod length change.

Note that the stock rockers come off the seat at approximately a 1.54 rocker ratio and the ratio increases during movement. Other rockers may come off the seat a a different ratio.

As stated above by badazz81z28, this method provides an approximation. The adjustable pushrod, although a direct measurement, is a better approximation. Since you are counting turns it is not super accurate and if you measure the adjustable pushrod with a vernier you get overall length and not gauge length that many vendors use to size pushrods. Counting turn provides a direct measurement of gauge length. Best check is to put a dial indicator on the rocker during installation and directly measure the preload. Since most lifters are pretty forgiving with preload these approximate methods work fine. However if you have a lifter with a tighter preload range (Morel, Comp R, etc.) than direct measurement with a dial indicator is a better way to go.

 

Ok, i get it. Thanks for your time and help. I hope i can get this thing running now.

 

Good luck