So I'm about to do my valve seals. For reinstallation, do I just tighten the rocker nut down until there is no more gap (play) where the rocker engages the pushrod? I imagine the valves must be fully closed (off the cam lobes).

 

Stock cam or aftermarket? Usually the cam company will indicate how much preload they want for that particular cam. For instance. my cam was 1/2 turn after 0 lash. 0 last is the point in which there is no vertical play in the push rod, but it still spins freely. And yes, you'll want it on the base circle of the cam.

Otherwise everyone's opinion differs. Most of the time it's between 1/4 of a turn and 1 full turn.

 

Stock everything.

 

I made this chart.
It works for any SBC 18436572 camshaft - mild or wild.
All you are doing is putting a lobe at max lift, and adjusting the rocker for the lobe 180 degrees opposite at minimum lift.

 

Thanks! Great chart. Anyone sell a damper sticker that has the degrees marked?

 

There's a few. Mr. Gasket makes one. Moroso has one. Etc. The local O'Reilly carried some. Make sure you get the one specified for the correct diameter dampener. Make sure you thoroughly clean the dampener, otherwise you'll lose the sticker the first time you kick the go stick.

 

I made a few docs to help me and thought I would share. One is the combined table plus a crank rotation add-on from NE84TA's post and the other is a 6-3/4" damper face template for indexing.

PLEASE DOUBLE CHECK so that I can make sure these are correct. I can fix them if needed.

Thanks!

 

Eeeeeeziest way to find the "zero" point, is the "EOIC" method.

Which is short for, "Exhaust Opening, Intake Closing".

THIMK about a complete engine cycle for a minute. Start, for the sake of argument, at firing. Suck, squeeze, bang, blow. Let's start at bang.

The engine is at TDC, and the spark plug lights. The air/fuel mixture begins to burn. The pressure in the cyl rises as the gases heat up, generating pressure on the top of the piston that pushes it down. This applies power to the crankshaft and is what moves the car. We call it the "power" stroke. "Bang".

Presently the piston reaches the bottom, and all possible power has been extracted from the hot gas in the cyl which is now a good bit cooler. The exh valve begins to open. At this point, the engine has turned 180° from firing.

The piston moves back up as the exh valve is open, pushing gas out the exh valve. We call this the "exhaust stroke" aka "blow".

Presently the piston returns to the top of the cyl. We're now 360° of crank rotation - one full revolution - from firing. I.e., we're back to TDC, but NOT to firing. At this point, the exh valves closes, and the int begins to open. Since the exh valve began to open at the beginning of the exh stroke and re-closed at the end, then right in the middle - with the piston halfway up - is the max exh valve opening.

So we're back at TDC, the exh valve is closing and the int is opening. The piston begins to go back down, with the int open. Air/fuel is drawn into the cyl. As the piston reaches BDC, the int closes; and like the exh stroke, somewhere near about halfway down, the int reaches full open as it goes through its while cam lobe function. This is of course the "intake stroke". "Suck". The end of it is at 360° + 180 ° from firing; 540°. 1½ revolutions.

Then the piston reaches BDC, the int valve closes, and the piston begins to return to the top, compressing the mixture. 180° later it reaches TDC for a 2nd time, and the spark occurs. We're in "squeeze" until we reach "bang" again.

Not too hard to imagine a cam lobe... kinda egg-shaped, with a sorta pointy end and a sorta blunt end, directly opposite each other. Pointy end = max lift; blunt end = zero lift. So if you wanna find "zero", all ya gotta do is, find MAX lift, and then 360° of crank rotation from there, is zero. Since the cam turns at half the rate of the crank, then 360° of crank rotation = 180° of cam rotation, IOW, we get from the pointy end of the lobe to the blunt end, in one full turn of the crank.

So, go back to the above description of valve motion. Max exh lift occurs about 180° or crank rotation before max int lift. Therefore zero exh lift occurs about 180° AFTER max int lift... IOW, shortly after the int closes.

Which tells you, adjust each cyl's exh, shortly after that same cyl's int has just closed. That's the "IC" in "EOIC".

Similarly, max int lift occurs shortly before the exh opens. The "EO" in "EOIC".

So now you know: turn the motor by hand until you see a cyl's int close; say, #2. Turn the engine some more, just a bit less than 90° more, and at that point, it will be time to adjust the into of the next cyl in the firing order. The "bigger" your cam (longer duration) the less rotation will elapse between #2 int close and #1 int on absolute dad nutz zero. In the real world, if you turn the motor until you see #1 int reach full opening and then come back down, you can adjust its exh just before its int fully closes.

And similarly, you would adjust the #1 int just as its exh begins to open.

Once you find one of those points for one kind of valve, say #1 int closing, you can adjust #1 exh; then turn the motor exactly 90° and adjust the exh valve on the next cyl in the firing order (#8); then another 90° and adjust the #4 exh; and so forth. Then follow the same principle looking at exh opening and adjust the int accordingly.

The other way of doing the same thing is to watch each valve for max lift, and when that it reached, adjust the same valve on the cyl 4 cyls away in the firing order. I.e., 18436572: when #1 int is full open, adjust #6 int; turn 90°, #8 int will be full open, adjust #5 int; and so on. Then the same for exhausts.

Too simple.

Adjust until all the VERTICAL play in the push rod (banging it up and down) goes away. DO NOT try to "twist" the push rod!!! you WILL screw up if you do that. They will be WAAAAAAYYYYY too tight. Vertical play ONLY!!!!!!

Then once you've set all the valves to "zero" that way, add your desired preload to all 16. Typical preload for a street motor such as anything with TPI on top of it will be ½ to ¾ turn on the nut. The exact value you use is not as important as making sure they're ALL THE SAME. I'd suggest using ½ turn myself.

 

Yes Tootie, your degree wheel is perfect. Just tape it to your balancer.

And sofa gave another explanation for what I was trying to show. Thanks.

The other way of doing the same thing is to watch each valve for max lift, and when that it reached, adjust the same valve on the cyl 4 cyls away in the firing order. I.e., 18436572: when #1 int is full open, adjust #6 int; turn 90°, #8 int will be full open, adjust #5 int; and so on. Then the same for exhausts.

Too simple.

Adjust until all the VERTICAL play in the push rod (banging it up and down) goes away. DO NOT try to "twist" the push rod!!! you WILL screw up if you do that. They will be WAAAAAAYYYYY too tight. Vertical play ONLY!!!!!!

Then once you've set all the valves to "zero" that way, add your desired preload to all 16. Typical preload for a street motor such as anything with TPI on top of it will be ½ to ¾ turn on the nut. The exact value you use is not as important as making sure they're ALL THE SAME. I'd suggest using ½ turn myself.

If your intake manifold is off, then you can watch for the pushrod cup of the lifter you are removing the lash to just separate from the lifter's snap ring. This is zero lash - all clearance removed. Then add your additional 1/2 to 3/4 turn of preload. Done.

 

Thanks. Easy enough!

When you guys say do not "twist" the pushrod, what do you mean?

 

spinning it between your finger and thumb while tightening. Up/down only.

 

Some people spin the pushrod to try and tell where zero lash is. When they start to feel drag, they think that's zero lash. Really though, zero lash is when there is no vertical movement between the rocker arm and the lifter.

 

Yes, and even Comp Cams changed the instructions on their website a few years ago by removing the "twist the pushrod until you feel a slight drag".
It's the vertical movement of the pushrod between the lifter and the rocker arm that you are trying to adjust to zero lash (and not beyond that until you add preload)...