push rod length
09-21-2009, 07:30 PM
#1
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push rod length I have a 99 ls1 that I'm going to install a set of stock 243's and a 228r cam.
The lifters will be replaced with ls7 lifters any idea on what the push rod length should be?
I know I should use a push rod length checker but I will only have the weekend to do the swap so I need to have some options there when it comes down to it. I already have a set of 7.4 but from what I read those are to long.
The lifters will be replaced with ls7 lifters any idea on what the push rod length should be?
I know I should use a push rod length checker but I will only have the weekend to do the swap so I need to have some options there when it comes down to it. I already have a set of 7.4 but from what I read those are to long.
09-23-2009, 04:52 AM
#6
Buy an adjustable pushrod and measure while its apart. That way if the ones you purchased are the wrong length you can assess the consequences of using them to re-assemble the car and order new ones if required. This allows you to re-assemble over a weekend.
Guessing and then not verifying the length is asking for trouble. Better to find out the correct length while its apart then later when something more serious happens.
Guessing and then not verifying the length is asking for trouble. Better to find out the correct length while its apart then later when something more serious happens.
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09-23-2009, 10:54 AM
#8
Easy trick I learned from harland sharp during rocker install was to make sure that you have 1 turn to 1 1/2 turns from the zero lash position. Make sure what ever cylinder you are checking that the valves would be closed and you are riding on the base circle of the cam not the lobe. I did use a length checker for my install but was able to verify push rod length when I got the right number of turns. If you have access to a couple of different length push rods you can use them until you get the correct number of turns. From what I have seen 7.4's should probably give you about 1 1/2 to 1 3/4 turns of pre-load. Hopefully your setup works out to be the same. Good luck.
09-23-2009, 11:43 PM
#10
I have never heard that 1 1/2 turns is worth .117 of preload. Maybe around .090 at the most. Well within the limits of any GM lifter. I seem to remember someone using a dial indicator to get that number. Just curious how did you come up with the .117?
09-24-2009, 06:37 AM
#11
(1.25 mm per turn X 1.5 turns)/25.4 mm per inch = 0.074"
0.074" X 2.7/1.7 = 0.117" (Using parallel triangles and the valve stem as a fixed point, the rocker rotates about the valve stem to compress the lifter as you tighten the bolt. Since the measurement being used is 1.7 from the fixed point and the rocker ratio is 1.7:1, then the pushrod is 2.7 from the fixed point. So as you tighten the bolt, the pushrod end moves more than the bolt by the ratio of 2.7/1.7. I have verified this with a dial indicator and it is pretty close to within a few thousandths.)