I'm asking more valvetrain questions (and hopefully answering some) because there seems to be 2 schools of thought here, and I know myself and others could sure use some clarification. Please add your 2 cents so that we can hopefully cover this topic in one thread
. I've searched the archives and have gotten conflicting info..... Some members say there is no lash to adjust (correct) but there is "preload
" when changing valvetrain geometry. I've installed a Crane cam 260 h (#863904 ) into a fresh (1987 360) longblock. So all torque and firing order specs are for that engine.
The following info is from Crane and mixed in with my 2 cents....
What is Hydraulic Lifter Preload?
Mechanical cam designs require a running clearance or valve lash, while hydraulic lifters are just the opposite. 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. See figure below.
I checked my lifter preload with the following quik method. There is another method listed at the end of this post.
Now If I did this wrong somebody chime in
With the cam , hydraulic lifters and pushrods in place...
(Tip) Using the firing order (1,8,4,3,6,5,7,2). Align your timing marks and bring #1 up on the compression stroke. Making sure lifters are on the *base circle each time. (At this position the valve springs are at their least amount of tension making the job a little easier to do.) Install your pushrods and rockers arms in pairs torque them equally, alternate between the 2 nuts and tighten to 19 ft lbs. Turning engine by hand clockwise 1/4 turn will bring your next cylinder in the firing order up on the compression stroke and the lifters on the base circle (always check though).
Wait a few minutes, allowing the lifters to bleed down. Now, lay a rigid straightedge across the cylinder head, supporting it on the surface of the head where the valve cover gasket would go. Using a metal scribe and the straightedge, carefully scribe a line on both pushrods. Now carefully remove the torque from all valve train bolts. Do this in the same order as assembly and loosen nuts in prs equally, so as not to twist the bridges. Wait a few minutes for the pushrod seat in the hydraulic lifter to move back to the neutral position. Carefully scribe a new line on both pushrods.
Measure the distance between the two scribe marks, it represents the amount of lifter preload. If the lines are .020" to .060" apart you have proper lifter preload. If the lines are the same or less than .020" apart you have no, or insufficient, preload. If the lines are further apart than .060", you have excessive lifter preload.
My preload ended up being .097
What happens if the amount of Hydraulic Lifter Preload is wrong?
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.
Ok since my preload worked out to be .097 it's out of "spec" for my cam. I need to adjust it. The cam kit comes with "shims" but some members say that this messes up the cam geometry again sooo....Do I use shims or buy different pushrods??? Also has anyone ever used locktite to secure the rocker bolts ???
Methods to Adjust for Proper Hydraulic Lifter Preload
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!
Do Hydraulic Lifters Need to be Primed with Oil?
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.
*Base circle of cam shown below.
Adjusting Hydraulic Lifters for Proper Preload
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.
Sorry if this was long, but I was confused and still have questions.