Lifter pre-load measurements
02-10-2005, 10:41 AM
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Lifter pre-load measurements I've noticed a number of people asking about lifter pre-load situations other than the stock lifter/stock pushrod/unmilled head setup. On any other setup you should be mindful of lifter pre-load, especially when using a lifter like the Comp R. Of course you may have dumb luck, especially when using the stock lifters which allow a lot of installer error. In any case, read on if you want to do things the "right" way.
You can easily measure the amount of pre-load on the lifter after you bring the system to ZERO LASH. At zero lash the pushrod will not longer swivel because there is too much pressure on it from the rocker and lifter.
Once you reach zero lash, an easy way to tell the amount of pre-load is the amount that you turn the rocker bolt. I believe the rocker bolt has an M6x1.0 thread. What actually matters is the thread pitch. With metric bolts, the thread pitch describes the distance between threads. With a 1.0 thread pitch- 1 turn = 360 degrees = 1.0mm of downward movement. With that in mind, simply determine the amount of desired pre-load, and you can figure out the number of degrees to turn the rocker bolt:
Preload needed: .008"
Degrees needed to turn bolt head = x degrees
1 complete bolt head revolution (360 degrees) = 1mm/25.4mm = .03937"
.008" / x degrees = .03937"/360 degrees
(360 degrees x .008")/.03937" = x degrees
x = 73.15 degrees
73 degrees/360 degrees = .203 = 1/5 of a turn
Feel free to make corrections if you think this is wrong. Hopefully this will clear up the incorrect use of LASH and PRE-LOAD and help people accurately find your pre-load either eyeballing it, or more accurately with a dial gauge.
You can easily switch a different metric thread pitch into this formula, though realize that SAE measure threads per inch which will lead to some slightly different equations:
SAE- 5/16"-18 TPI
18 threads per inch
The distance from one thread to the next is 1/18". This equals .055". So one 360 degree revolution will give .055" of downward movement. Plugging this into the equation above:
Desired pre-load= .008"
Degrees needed to turn bolt head = x degrees
1 bolt head revoltion (360 degrees) = .055"
.008"/x degrees = .055"/360 degrees
(360 degrees x .008") / .055" = x degrees
x degrees = 52.36 = .14 turns
Feel free to make corrections if you think this is wrong. Hopefully this will clear up the incorrect use of LASH and PRE-LOAD and help people accurately find your pre-load either eyeballing it, or more accurately with a dial gauge.
Remember, you cannot measure pre-load without first reaching zero lash.
Ben
You can easily measure the amount of pre-load on the lifter after you bring the system to ZERO LASH. At zero lash the pushrod will not longer swivel because there is too much pressure on it from the rocker and lifter.
Once you reach zero lash, an easy way to tell the amount of pre-load is the amount that you turn the rocker bolt. I believe the rocker bolt has an M6x1.0 thread. What actually matters is the thread pitch. With metric bolts, the thread pitch describes the distance between threads. With a 1.0 thread pitch- 1 turn = 360 degrees = 1.0mm of downward movement. With that in mind, simply determine the amount of desired pre-load, and you can figure out the number of degrees to turn the rocker bolt:
Preload needed: .008"
Degrees needed to turn bolt head = x degrees
1 complete bolt head revolution (360 degrees) = 1mm/25.4mm = .03937"
.008" / x degrees = .03937"/360 degrees
(360 degrees x .008")/.03937" = x degrees
x = 73.15 degrees
73 degrees/360 degrees = .203 = 1/5 of a turn
Feel free to make corrections if you think this is wrong. Hopefully this will clear up the incorrect use of LASH and PRE-LOAD and help people accurately find your pre-load either eyeballing it, or more accurately with a dial gauge.
You can easily switch a different metric thread pitch into this formula, though realize that SAE measure threads per inch which will lead to some slightly different equations:
SAE- 5/16"-18 TPI
18 threads per inch
The distance from one thread to the next is 1/18". This equals .055". So one 360 degree revolution will give .055" of downward movement. Plugging this into the equation above:
Desired pre-load= .008"
Degrees needed to turn bolt head = x degrees
1 bolt head revoltion (360 degrees) = .055"
.008"/x degrees = .055"/360 degrees
(360 degrees x .008") / .055" = x degrees
x degrees = 52.36 = .14 turns
Feel free to make corrections if you think this is wrong. Hopefully this will clear up the incorrect use of LASH and PRE-LOAD and help people accurately find your pre-load either eyeballing it, or more accurately with a dial gauge.
Remember, you cannot measure pre-load without first reaching zero lash.
Ben
Last edited by RX-Ben; 02-10-2005 at 03:20 PM.
02-10-2005, 11:13 AM
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WOW!! I did it a little different. I measured + .008. Then turned it back to zero. It took exactly a quarter turn. Then brought them all to zero added a quarter turn and called it a day! I'm sure your system will work also.
