help with getting pushrod size (VIDS)
06-26-2011, 06:41 PM
#41
Supplement Edit - Is this the answer?
https://ls1tech.com/forums/8261027-post11.html
Last edited by Darkman; 06-26-2011 at 06:57 PM.
06-27-2011, 04:21 AM
#42
That's part of the answer. I spent some time last year using Shane's method, a dial indicator measurement, calculations and my adjustable pushrod measurements when I did a pushrod change in my car. I found that all three come out close to each other but there are a few nuances. When you tighten the rocker bolt to zero lash and then torque to 22 lb-ft, I found that it takes 1/3 turn after the rocker bottoms in the stand to reach final torque. The rockers were pretty consistent with this 1/3 turn. Once the rocker bottoms in the rocker stand, there is no more preload applied to the lifter. So if you use 1 turn for zero lash to full torque, only 2/3 turn are actually applying preload (bringing the rocker down to seat in the stand). For that case I get the following:
2/3 X 1.25/25.4 X 2.7/1.7 = 0.52 (Shane gets around 0.049" for this case so they match pretty well)
When the number of turns increases to 1-1/4, you still need to subtract the 1/3 bolt turn after the rocker seats in the stand.
(1.25-0.3333) X 1.25/25.4 X 2.7/1.7 = 0.071
Note that all of these are approximate but given the pushrods are available only in increments of 0.025" any of the methods should work. What Shane recommends is using turns to figure preload and if a pushrod is the wrong length try a different length to obtain the correct range of turns on the bolt. The math allows you to estimate the new length if you don't have different lengths available and provides another tool to work with and double check your work. One other tool that a lot of guys overlook is they usually have the stock pushrods available that will provide an estimate of length when counting turns using Shane's method, but the stock length is 7.385" and not 7.400" (I and others have measured similar length of the stock pushrods) as is the internet myth.
2/3 X 1.25/25.4 X 2.7/1.7 = 0.52 (Shane gets around 0.049" for this case so they match pretty well)
When the number of turns increases to 1-1/4, you still need to subtract the 1/3 bolt turn after the rocker seats in the stand.
(1.25-0.3333) X 1.25/25.4 X 2.7/1.7 = 0.071
Note that all of these are approximate but given the pushrods are available only in increments of 0.025" any of the methods should work. What Shane recommends is using turns to figure preload and if a pushrod is the wrong length try a different length to obtain the correct range of turns on the bolt. The math allows you to estimate the new length if you don't have different lengths available and provides another tool to work with and double check your work. One other tool that a lot of guys overlook is they usually have the stock pushrods available that will provide an estimate of length when counting turns using Shane's method, but the stock length is 7.385" and not 7.400" (I and others have measured similar length of the stock pushrods) as is the internet myth.
06-28-2011, 09:42 PM
#45
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Anyway, since the base circle determines the distance from the pushrod cup to the lifter... as lift increases, the pushrod will need to be longer to make up the difference.
Shane
06-29-2011, 04:54 AM
#46
I'm actually a little suprised that you don't know why this is true. Think about this, in order to increase the lift of a given camshaft core size, the BASE CIRCLE MUST BECOME SMALLER. If you were to try and increase lift based on the actual distance from the centerline of the camshaft to the "top" of the lobe, the lobes would become "taller" than the camshaft bearing journals and the camshaft could not be physically inserted into the engine. Normally the highest point of the lobe is left constant with the base circle being made smaller. I thought this was common knowlege. I guess that is why I'm having such a hard time explaining these concepts here. If anyone is good with CAD maybe they could visually explain this.
Anyway, since the base circle determines the distance from the pushrod cup to the lifter... as lift increases, the pushrod will need to be longer to make up the difference.
Shane
Anyway, since the base circle determines the distance from the pushrod cup to the lifter... as lift increases, the pushrod will need to be longer to make up the difference.
Shane
No, I understand that. Your prior statement was "...I have no idea how anyone is getting less than a 7.400" pushrod with a .600"+ lift cam in an otherwise stock combo."
The way I interpreted your statement was that a cam under 0.600" lift fell into another category then one over 0.600" and that was the point of confusion, at least for me.
06-29-2011, 02:57 PM
#48
Thanks to both of you and darkman for posting and helping out. All know what your talking about and put the time into figuring everything out. With what was said it looks like I could have really went with either the 7.375 or 7.400 so went with the shorter as it looked to get the preload right.
05-20-2012, 10:46 PM
#55
Its hard to tell from the video but one observation, the 10 turns looks like you are forcing it a bit and in the process pushing down with some force on the pushrod/lifter, which will give a bit. Be very very gentle when you move the tip up and down so no force is transferred through the rocker to the pushrod (like you are lifting the tip with a feather).
Looks to me like either 9.5 or 9.75 is in the ball park based on the videos on page 1.
One other note, if you need to alter the wipe by shimming or reducing the rocker height, this will also change the pushrod length. So if you plan to alter the wipe pattern at all do that first then measure.
Looks to me like either 9.5 or 9.75 is in the ball park based on the videos on page 1.
One other note, if you need to alter the wipe by shimming or reducing the rocker height, this will also change the pushrod length. So if you plan to alter the wipe pattern at all do that first then measure.
I brought this thread back from the dead.
Vettenuts, your post kind of confuses me a bit. You say 9.5 to 9.75 is in the ball park, but the rockers still rattle up and down. Do you consider that zero lash?
9.75 jiggles up and down, so isnt 10 turns ideal for zero lash?
05-21-2012, 12:46 AM
#56
I don't see why people are so confused. I just did this tonight. I'm used to setting valve lash on flat tappets so i turned the checker out 10 turns, torqued the stand down, and measured how much lash there was with a feeler gauge.
10 turns = 0.500, length of checker = 6.800, used 2 0.025 feeler gauges to get zero lash. SO 0.500 + 6.800 + 0.050 feeler gauge equals a 7.350" fushrod for ZERO lash. Add in whatever preload you want:
.050 = 7.4"
.060 = 7.41
.070 = 7.42"
.075 = 7.425"
.080 = 4.43"
I'm going to order 7.400" and call it a day
EDIT: wait a second now i think i f'ed myself...didn't take into account the ration on the rocker. i'll think about it more at work tomorrow lol
10 turns = 0.500, length of checker = 6.800, used 2 0.025 feeler gauges to get zero lash. SO 0.500 + 6.800 + 0.050 feeler gauge equals a 7.350" fushrod for ZERO lash. Add in whatever preload you want:
.050 = 7.4"
.060 = 7.41
.070 = 7.42"
.075 = 7.425"
.080 = 4.43"
I'm going to order 7.400" and call it a day
EDIT: wait a second now i think i f'ed myself...didn't take into account the ration on the rocker. i'll think about it more at work tomorrow lol
05-21-2012, 01:44 AM
#57
Not sure what you mean by that. Seems you did it right. Find the pushrod length that gives you zero lash with the rocker arm bolt torqued to 22 ft-lbs, and add what ever lifter pre-load you're after.
05-21-2012, 08:44 AM
#58
05-21-2012, 07:51 PM
#59
Zero lash is when all up/down pushrod movement is gone. You should hear a little clicking and feel it too, then a bit more length on the pushrod would make that all that disappear ... that's the point of zero lash.
05-21-2012, 07:55 PM
#60
That video shows a rocker way loose and was told thats zero lash.