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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
How do you guys like to adjust your valves with hydraulic flat-tappet cams? Do you ever get them too tight where the valves don't seat all the way, resulting in no compression?...
In my experience, the only way to adjust the lash and result in the valve being off it's seat is to travel through the entire plunger range in the lifter and bottoming it out.
I can't recall exactly what the travel is although .200" comes to mind. That's several turns of a typical Gen 1 SBC adjusting nut of 3/8"-24.
I prefer to do them with the engine running, fully hot. Back each one off until it clacks; tighten until it just quits; move to the next as fast as possible to minimize the mess. Shut engine off and add desired preload. Typical preload values are 1 full turn from the factory, 3/4 for a Chilton's type repair, 1/2 for what most people here are doing (hot street), 1/4 or less for pure race where you'll be back in there regularly.
In that case, I use the traditional approach with the cam is in the proper spot for each cylinder and adjust the lash based on valve train movement. Specifically, if the pushrod can rotate and to what degree. Get it snug, then add a 1/4 to 1/2 turn for preload. A little on the loose side wouldn't hurt anything for the break-in. It's something you'll revisit soon enough.
Curious though as to what led you ask this question in the first place.
Originally Posted by T.L.
Do you ever get them too tight where the valves don't seat all the way, resulting in no compression?...
In that case, I use the traditional approach with the cam is in the proper spot for each cylinder and adjust the lash based on valve train movement. Specifically, if the pushrod can rotate and to what degree. Get it snug, then add a 1/4 to 1/2 turn for preload. A little on the loose side wouldn't hurt anything for the break-in. It's something you'll revisit soon enough.
Curious though as to what led you ask this question in the first place.
I originally adjusted the valves 2 years ago on an engine stand, going by the Chevy book. It said 1 full turn past zero lash, which sounded like a lot to me, but I did it. This past weekend, now with the engine in the car, tried to fire it up and had NO compression in any of the cylinders.
Re-adjusted them using the 90-90-90-90 method. Same problem. After backing off about 3/4 turn, there is compression, but I haven't fired up the engine yet. Really don't wanna destroy this new cam. Not sure why this is so difficult. It's like it doesn't want any pre-load beyond zero lash...
I originally adjusted the valves 2 years ago on an engine stand, going by the Chevy book. It said 1 full turn past zero lash, which sounded like a lot to me, but I did it. This past weekend, now with the engine in the car, tried to fire it up and had NO compression in any of the cylinders.
Re-adjusted them using the 90-90-90-90 method. Same problem. After backing off about 3/4 turn, there is compression, but I haven't fired up the engine yet. Really don't wanna destroy this new cam. Not sure why this is so difficult. It's like it doesn't want any pre-load beyond zero lash...
Don't use the 90-90-90-90 method for a performance cam. You need to adjust the intake when the exhaust is at full lift and the exhaust when the intake is at full lift. To adjust, jiggle the pushrod in an up and down motion while slowly tightening the rocker nut until right at the point there is no more UP and DOWN movement - that's zero preload.
What lifters were used? After set to zero, if they're Comp Magnum lifters they need no more than 1/8" turn (I ran mine at 1/16 turn after break-in). Their Race hydraulics 1/8-1/4 turn, and the Hi-Tech lifters 1/4-1/2 turn. If value priced lifters, I'd do a 1/4 turn. I'd always run the car a few miles (after changing the break-in oil) to make sure the cam was fully "broken-in", then go back and do another adjustment. If all is well and the cam doesn't start going away on you, or the nuts hold their adjustment, you shouldn't have to readjust again - at least I never had too.
If you use the other valve on the same cyl as the reference, the correct point for adjustment is the "EOIC" method. The intake should be adjusted when the exhaust valve is just beginning to open ("Exh Opening") and the exhaust should be adjust as the intake is just closing ("Int Closing").
The absolute best method though, is to watch the same valve, on the cyl 4 cyls away in the firing order. So for example, you'd adjust the #1 intake when the #6 intake is at full opening... the cam turns 180 degrees in between those 2 points, meaning, those 2 lobes are exactly opposite each other. Peak lift is exactly opposite minimum lift, that is, those 2 points are 180 degrees apart. So if you find one int that's at full open, you adjust the corresponding other int (let's say, if you see that #4 exh happens to be full open, you'd adjust 7 exh); then turn the crank exactly 90 degrees and adjust the next firing cyl's exhaust which would be #8; turn another 90 degrees, adjust #1 exh; and so on; then once all of one kind are done, repeat the process for the other kind.
The up/down push rod motion however, is EXACTLY correct. DO NOT UNDER ANY CIRCUMSTANCES fall for the "twist the push rod" EFFFFF-UP. You will end up with them WWWWWAAAAAAAAAAAYYYYYYYYYYY too tight, every time. Adjust only as tight as to take up all of the vertical play in the push rod when that valve's lobe is directly opposite peak lift. That's actually probably your problem at the moment.
Then once you have all of them set to zero lash that way, add your desired preload. I suggest 1/2 turn.
In the end though, as long as the motor will start and run at least halfway decent, it'll be "close enough" to begin with; then after it's finished with break-in, go back and adjust them with the motor running.
Last edited by sofakingdom; Oct 8, 2020 at 04:47 AM.
The up/down push rod motion however, is EXACTLY correct. DO NOT UNDER ANY CIRCUMSTANCES fall for the "twist the push rod" EFFFFF-UP. You will end up with them WWWWWAAAAAAAAAAAYYYYYYYYYYY too tight, every time. Adjust only as tight as to take up all of the vertical play in the push rod when that valve's lobe is directly opposite peak lift. That's actually probably your problem at the moment.
It would seem your feel for rotation vs up and down is different than my own. I do believe I understand where you see one method yielding different results than the other but after some practice, it's all the same. It's all in the fingertips...Of course this is just personal preference. In all truthfulness I go about it both ways. And possibly more.
Zero lash means that the pushrod seat is still up against the snap ring / retainer with all vertical clearance removed. As soon as the the seat is no longer in contact with the snap ring, you are in the "lash zone". That clearance is the preload you are adjusting for by turning the rocker's adjusting nut down your additional 1/4 to 3/4 turn.
You should also consult your lifter manufacturers specs. My Johnson lifters specify 0.035" +/- 0.010" pre-load. With the 24 tpi ARP studs, one full turn is 0.041". So I set my poly locks at 3/4 turn plus the "bump" of the wrench to set the poly lock on top of the stud. You will know you are doing them at the right spot on the cam lobe when all the poly locks have the same thread exposure.
Right - use Comp's spec for pre-load (I don't know it but Comp will) and use your threads-per-inch of your rocker studs to mathematically determine your pre-load.
Wow, this some good info. I never knew different brands of lifters had different preload requirements.
And I have never seen details like this anywhere - except here on ThirdGen.org.
Last edited by NoEmissions84TA; Oct 9, 2020 at 11:42 PM.
