What is preload?
08-01-2009, 08:05 PM
#3
When the rocker arm assembly is properly torqued down into position, the pushrod must take up all the clearance and descend into the hydraulic lifter, causing the pushrod seat to move down by .020" to .060". The distance that the pushrod seat moves down away from the retaining lock is the "Lifter Preload". The hydraulic mechanism requires this precise amount of "preload" for it to do its job properly.
If clearance exists between the pushrod and the seat in the hydraulic lifter, after the rocker arm assembly has been torqued down, you will have no lifter preload. In this case the valve train will be noisy when the engine is running. All of the hydraulic force produced by the lifter will be exerted against the lifter's retaining lock, and this could cause the lock to fail. If the opposite occurs and the pushrod descends too far (more than .060"), then you have excessive lifter preload. In theory, a hydraulic lifter can pump up whatever preload you put into it.
Therefore with excessive preload, as the engine RPM and oil pressure increases, the hydraulic mechanism will pump-up the pushrod seat. This will cause the valve to be open longer and the lift to be higher. This will decrease the cylinder pressure, lowering the performance of the engine. If the preload is excessive it may cause "backfiring" from the engine.
There are several different methods for increasing or decreasing the amount of lifter preload, depending on valve train design and how the rocker arm is held onto the cylinder head. What may work on one year's engine may not work for another, even though they are basically the same engine. There is one method that universally works on all engines, change the pushrod length!
Many people mistakenly believe that hydraulic lifters must be soaked in oil overnight and be hand pumped up with a pushrod before installing into a new engine, however this is not necessary. In fact, this could cause the lifter to act as a "solid" and prevent obtaining proper preload. What is very necessary is the priming of the entire engine's oil system before starting up a new engine for the first time. This is done by turning the oil pump with a drill motor to force oil throughout the entire engine.
In order to adjust the preload, the lifter must be properly located on the base circle or "Heel" of the lobe. At this position the valve is closed and there is no lift taking place. You will need to watch the movement of the valves to determine which lifter is properly positioned for adjusting.
1. Remove the valve covers, and pick a cylinder that you are going to set the preload on.
2. Hand rotate the engine in its normal direction of rotation and watch the exhaust valve on that particular cylinder. When the exhaust valve begins to open, stop and adjust that cylinder's intake rocker arm. (Why? Because when the exhaust valve is just beginning to open, the intake lifter will be on the base circle of the lobe, the correct position for adjusting the intake.)
3. Back off the intake rocker arm adjuster and remove any tension from the pushrod. Wait a minute or two for that hydraulic lifter to return to a neutral position. The spring inside the lifter will move the pushrod seat up against the retaining lock if you give it time to do so. (If you are installing brand new lifters they will be in the neutral position when they come in the box.)
4. Now spin the intake pushrod with your fingers while tightening down the rocker arm. When you feel a slight resistance to the turning of the pushrod, you are at "Zero Lash". Turn the adjusting nut down one half to one full turn from that point. Lock the adjuster into position. The intake is now adjusted properly.
5. Continue to hand turn the engine, watching that same intake. It will go to full open and then begin to close. When it is almost closed, stop and adjust the exhaust rocker arm on that particular cylinder. (Again, when we see the intake almost closed, we are sure that exhaust lifter is on the base circle of the lobe.) Loosen the exhaust rocker arm and follow the same procedure described before in steps 3 and 4 to adjust this rocker arm.
6. Both valves on this cylinder are now adjusted, and you can move on to your next cylinder and follow the same procedure again.
Make sure you know your tolerances something like a Comp "R" needs to be done when its warm it NEEDS adjustable rockers and it has a preload of .002 to .004 as to an LS7 lifter is between .066 to .097 depending on how quiet you want that valve train too be the deeper the number the quieter the valve train, and you don't need and adjustable valve train (rockers) to set them correctly. Do you see the differences in the amount of "space" u have to work with.
Hope this helped.
If clearance exists between the pushrod and the seat in the hydraulic lifter, after the rocker arm assembly has been torqued down, you will have no lifter preload. In this case the valve train will be noisy when the engine is running. All of the hydraulic force produced by the lifter will be exerted against the lifter's retaining lock, and this could cause the lock to fail. If the opposite occurs and the pushrod descends too far (more than .060"), then you have excessive lifter preload. In theory, a hydraulic lifter can pump up whatever preload you put into it.
Therefore with excessive preload, as the engine RPM and oil pressure increases, the hydraulic mechanism will pump-up the pushrod seat. This will cause the valve to be open longer and the lift to be higher. This will decrease the cylinder pressure, lowering the performance of the engine. If the preload is excessive it may cause "backfiring" from the engine.
There are several different methods for increasing or decreasing the amount of lifter preload, depending on valve train design and how the rocker arm is held onto the cylinder head. What may work on one year's engine may not work for another, even though they are basically the same engine. There is one method that universally works on all engines, change the pushrod length!
Many people mistakenly believe that hydraulic lifters must be soaked in oil overnight and be hand pumped up with a pushrod before installing into a new engine, however this is not necessary. In fact, this could cause the lifter to act as a "solid" and prevent obtaining proper preload. What is very necessary is the priming of the entire engine's oil system before starting up a new engine for the first time. This is done by turning the oil pump with a drill motor to force oil throughout the entire engine.
In order to adjust the preload, the lifter must be properly located on the base circle or "Heel" of the lobe. At this position the valve is closed and there is no lift taking place. You will need to watch the movement of the valves to determine which lifter is properly positioned for adjusting.
1. Remove the valve covers, and pick a cylinder that you are going to set the preload on.
2. Hand rotate the engine in its normal direction of rotation and watch the exhaust valve on that particular cylinder. When the exhaust valve begins to open, stop and adjust that cylinder's intake rocker arm. (Why? Because when the exhaust valve is just beginning to open, the intake lifter will be on the base circle of the lobe, the correct position for adjusting the intake.)
3. Back off the intake rocker arm adjuster and remove any tension from the pushrod. Wait a minute or two for that hydraulic lifter to return to a neutral position. The spring inside the lifter will move the pushrod seat up against the retaining lock if you give it time to do so. (If you are installing brand new lifters they will be in the neutral position when they come in the box.)
4. Now spin the intake pushrod with your fingers while tightening down the rocker arm. When you feel a slight resistance to the turning of the pushrod, you are at "Zero Lash". Turn the adjusting nut down one half to one full turn from that point. Lock the adjuster into position. The intake is now adjusted properly.
5. Continue to hand turn the engine, watching that same intake. It will go to full open and then begin to close. When it is almost closed, stop and adjust the exhaust rocker arm on that particular cylinder. (Again, when we see the intake almost closed, we are sure that exhaust lifter is on the base circle of the lobe.) Loosen the exhaust rocker arm and follow the same procedure described before in steps 3 and 4 to adjust this rocker arm.
6. Both valves on this cylinder are now adjusted, and you can move on to your next cylinder and follow the same procedure again.
Make sure you know your tolerances something like a Comp "R" needs to be done when its warm it NEEDS adjustable rockers and it has a preload of .002 to .004 as to an LS7 lifter is between .066 to .097 depending on how quiet you want that valve train too be the deeper the number the quieter the valve train, and you don't need and adjustable valve train (rockers) to set them correctly. Do you see the differences in the amount of "space" u have to work with.
Hope this helped.
08-02-2009, 01:40 AM
#6
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If you already have pushrods, your preload (right or wrong) has already been decided.
The proper way to do this is to assemble the engine/heads, measure for pushrod length, add your desired lifter preload to the measurement, and order that length pushrod.
08-02-2009, 01:21 PM
#7
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I called TSP told em what I was getting and John said those were the pushrods I should go with. Other than that to check pushrod length you buy a pushrod checker and torque down the rocker to spec right?
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08-02-2009, 05:03 PM
#8
Don't go with what any one says to go with. Do it right the first time. Get your checker check those lengths and buy the correct rod length as per the PR length measure. Unless you are using stock lifters for a stock cam you should always check the rod length I don't care how many people tell you other wise. Its your ride, your car, your pocket book that gets affected.
