73-87 Chevy _ GMC Trucks > Engine/Drivetrain
SBC 350 Hydraulic Valve Lash Adjustment
cosmic_3000:
Hello all,
I recently removed the heads on my 350, and during reassembly it was time for the valve lash adjustment. Just to note I didn't remove the lifters, they stayed in their bore, I just pulled the pushrods out. Engine hasn't ran in about 2 months.
Now during reinstall, I adjusted it this method:
- Turn engine #1 TDC, and adjust intake valves 1, 2, 5, 7, and exhaust valves 1, 3, 4, 8.
- Turn engine 360 degrees to #6 TDC, and adjust intake valves 3, 4, 6, 8, and exhaust valves 2, 5, 6, 7.
- For adjustment, I tightened until there was no vertical movement in the pushrod, then 1/2 turn more.
I thought that was everything that needed to be done, no? The pushrods were tight when I finished, but the next morning I went out and check, and I could turn them by hand again.
I'm not sure if my valves need more adjusting.
Thanks for your help!
JohnnyPopper:
You mean you could turn the push rods by hand, right?
Not unusual, your lifters have some wear, so they won't have the spring they had when new.
All they need is a supply of oil/ pressure and they will tighten up just fine.
However, I always though it was 3/4 turn after zero lash? Someone will school us if needed. ::)
FlatBlack77:
I am pretty sure myself about the 3/4 of a turn past zero lash.
I always do the final adjustment with the engine running. But I am most definitely not looking to start an argument about it.
75gmck25:
I've always jiggled the pushrod up and down to check clearance. If you try to "feel" clearance by turning a rod that is well lubricted with oil it is much harder to estimate the zero clearance point.
Its easier to get a consistent "feel" by jiggling it up and down to find the zero clearance point where you can't feel it move. Then add the preload of about 1/2 turn.
Bruce
bd:
--- Quote from: cosmic_3000 on April 22, 2020, 03:25:22 PM ---Now during reinstall, I adjusted it this method:
- Turn engine #1 TDC, and adjust intake valves 1, 2, 5, 7, and exhaust valves 1, 3, 4, 8.
- Turn engine 360 degrees to #6 TDC, and adjust intake valves 3, 4, 6, 8, and exhaust valves 2, 5, 6, 7.
- For adjustment, I tightened until there was no vertical movement in the pushrod, then 1/2 turn more.
--- End quote ---
The method you described works fine for a stock-to-near-stock camshaft profile. Regarding the zero-lash hydraulic lifter preload adjustment, anywhere in the range of 1/2 to 1 full turn is suitable. The key is consistency in the preload from valve-to-valve; adjust all valves exactly the same.
FYI - In some high-performance applications, a smattering of builders recommend zero lash, zero preload to eliminate the possibility of lifter pump-up in the case of valve float. But, that sort of defeats the purpose of hydraulic lifters, and I don't condone the method. It is far better to employ the proper spring and retainer combination to match the cam's profile, the valvetrain mass, and the engine's purpose, being mindful to limit engine RPM to a safe level.
Regarding the "apparent loss of lifter preload" based on the ease of rotating some of the pushrods after the engine sets overnight without running, hydraulic lifters naturally bleed down under valve spring pressure given a sufficient amount of time. The greater the accumulated wear between the lifter piston and its bore, the quicker that bleed-down occurs. As long as a lifter is low on the camshaft lobe ramp when the engine stops rotating, there is an adequate range of internal motion with respect to the lifter piston within its bore to allow the lifter to bleed down without the piston bottoming in its bore. When this occurs, the valve spring pressure bearing down the length of the pushrod is relieved and the pushrod spins easily. If the lifter rests higher on the ramp of the lobe when the engine stops rotating, the lifter will still collapse but will bottom out holding the valve off of its seat and the pushrod will be difficult to spin using your fingers. As long as the valvetrain doesn't "clack" when the engine is started, there is no cause for alarm or worry.
Did these explanations adequately ease your concerns?
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