Are the push rods bad? is that why your replacing them? I understand the O-rings.
Always do these steps:
Rule 1
The engine must be COLD during adjustment….not hot, not warm, not cool…it must be cold. Why? The metal expands when the engine is hot. The barrels, heads and rockers grow taller when hot and contract when cold. If a pushrod/lifter is adjusted when the engine is hot, the valve may be forced open as the engine cools and contracts. A valve that is opened at the wrong time will cause a loss of compression at the very least. At most the extended valve will hit the ascending piston and bend necessitating a rebuild. This can also happen if the lifters are adjusted on a high spot of the cam lobe. More on this in a bit. The Pros can tweak a lifter adjustment while the engine is hot. They listen to the tappet noise when the engine is running and determine which of the four is making the noise. They can tell by the noise on how much to turn down or up the adjustment. Leave these smooth moves to the Aces as they are also capable of rebuilding your top end if they screw up.
Rule 2
Take nothing for granted in mechanics If unfamiliar with the lifter setup that is about to be adjusted always read THAT SPECIFIC manufacturers instructions. Sound stupid? Not really when you consider that the threads per inch on the adjusters vary from manufacturer to manufacturer. One source may say turn the adjuster down 5 full turns. Well 3 full turns is more when there is less threads per inch and it is less when there is more threads per inch.
Rule 3
Always ensure the lifter/tappet/pushrod is at its lowest point before adjusting or else all kinds of bad things can happen. I'll expand on this later.
Rule 4
If there are two lengths for the 4 pushrods, the longer ones go into the exhaust portions of the valve train which are at the extreme front and the extreme rear. If there are three lengths, put the longest in the front exhaust, the second longest in the rear exhaust and the two shortest ones in the middle on the intakes.
Rule 5
Adjusting the pushrods too loosely will result in too much clearance and excessive valve train noise. Do it too tightly and the valve will be held open causing a loss of compression and power at the least. Tighter still and an ascending piston will bend the open valve.
Rule 6:
Practice makes perfect.
Pre-adjustment Procedure
On all models except the 1990-99 Sportster which has one piece pushrod tunnels, push the spring retainer down. If you have paws the strength of Godzilla you can do this with your fingers. For the rest of us, there are various techniques. The one I use is with a slotted or flat-sided screwdriver. I wedge the slot, horizontally between a couple of head fins while the screwdriver shaft lays on top of the spring retainer. The leverage provided allows for the retainer to compress easily. This can be done with one hand. With the other use another slotted screwdriver or a set of needlenose pliers and remove the spring keeper.Now the lower cover can be easily pushed by hand over the upper cover exposing the adjuster mechanism.
Oil Seals
On 1978 and earlier models, a set of 12 cork washers are used to seal the various component pushrod tunnels at the top where they mate with the head, at the bottom where they rest against the tappet guide and in the middle underneath the spring retainer. Circa 1979 and later models use rubber o-rings. The corks and o-rings are not interchangeable since the mating pushrod tunnels are designed for either or but not both oil sealing methods. It is prudent to replace these seals every time an adjustment is made. I've learned to do this even if the seals look ok since doing the same job twice is a drag. This will necessitate removing the pushrods totally. This is no big deal. Undo the locking nut and turn the tappet adjuster down or the pushrod adjuster up as the case may be. Rotate the engine until the tappet, (lifter), is at its lowest point. At this point the pushrod can be removed.
Rotating the engine:
Remove the spark plugs. Why? There will not be any engine compression building up to make this easy job difficult. If the engine is out of the bike or the clutch is totally disengaged with the outer primary removed, the engine sprocket, which is attached to the engine shaft at the front of the primary chain case, will be free to move. There is a special tool for this rotation procedure but it is not required for the hobby mechanic. Put on some gloves and turn the sprocket until the tappet is at its lowest point. However, in most cases, the bike will be in your garage or on the side of the road. Put the bike in the highest gear possible. Why? The engine will rotate easier than if in a lower gear and it will rotate slower to enable a more precise determination of the lowest point of the lifter as it rotates over the cam lobe. A friend can roll the bike back or forward while you observe the lifter going up or down on the cam lobe. The rear wheel can be raised off the ground via a bike lift or put on a crate in order to manually rotate the rear wheel back and forth to obtain the lowest point on the lifter/cam lobe. As an exercise, rotate the rear wheel in first gear by hand while it is on a lift or a crate. Now put the bike in 4th gear and try it again. This will demonstrate the reason for doing this procedure in a higher gear.