Adjusting valves on a Chevy 350 is one of those classic garage rites of passage that every small-block owner eventually has to tackle. If you've started hearing a rhythmic clicking sound coming from under your hood—often described as a "sewing machine" noise—or if your engine just isn't idling as smoothly as it used to, it's probably time to pull those valve covers. While it might seem a bit intimidating to mess with the internal "heartbeat" of your engine, the 350 is actually one of the most forgiving and straightforward engines to work on.
You don't need a doctorate in mechanical engineering to get this right. You just need some basic tools, a bit of patience, and a clear understanding of what "zero lash" actually feels like. Whether you've just finished a fresh rebuild or you're just trying to quiet down an old workhorse, getting your lifters set correctly will make a world of difference in how that V8 breathes and performs.
Getting Your Tools and Space Ready
Before you get your hands dirty, you'll want to gather a few things. You're going to need a basic socket set, a ratchet, and a way to turn the engine over by hand—usually a large socket on the harmonic balancer bolt does the trick. If you're planning on doing this while the engine is running (we'll get to that in a minute), you're definitely going to want some oil deflectors or an old valve cover with the top cut out. Trust me, skipping this leads to a face full of hot oil and a mess on your driveway that you'll be cleaning up for weeks.
Cleanliness is your friend here. Before you even loosen a single bolt on the valve covers, take a rag and wipe down the area around them. You don't want any stray dirt or old grease falling into the head once those covers are off. It's also a good idea to have some fresh valve cover gaskets on hand. It's pretty rare to get the old ones off without them tearing, and for the few bucks they cost, it's worth the peace of mind to avoid leaks later.
Understanding the Goal: Zero Lash
The most important concept to grasp when adjusting valves on a Chevy 350 is zero lash. This is the point where all the slack is taken out of the valvetrain, but you haven't actually started compressing the plunger inside the hydraulic lifter yet.
If you leave too much slack, you get that annoying clattering sound, and your valves won't open as far as they should, which kills power. If you go too tight, the valves might stay slightly open all the time, which can lead to burnt valves and a rough-running engine. The "sweet spot" is finding that exact moment where the pushrod stops moving up and down but can still be spun between your fingers.
Method 1: The Static Adjustment (Engine Off)
Most builders prefer the static method because it's clean and precise. You'll be doing this with the engine off, usually starting at Top Dead Center (TDC) for the number one cylinder.
Finding Top Dead Center
To start, you need to bring the #1 piston to the top of its compression stroke. You can do this by sticking a finger over the spark plug hole while someone else turns the crank; when you feel air blowing out, you're on the compression stroke. Align the mark on your harmonic balancer with the "0" on the timing tab.
The EOIC Rule
A lot of guys use the "EOIC" rule, which stands for Exhaust Opening, Intake Closing. It sounds fancy, but it's simple: 1. To adjust the intake valve, turn the engine until the exhaust valve on that same cylinder just starts to open. 2. To adjust the exhaust valve, turn the engine until the intake valve on that same cylinder has opened all the way and is almost closed.
When you're at the right spot, loosen the rocker arm nut until the pushrod can move up and down. Slowly tighten the nut while wiggling the pushrod up and down with your other hand. The second that "clunking" or vertical movement stops, you've hit zero lash.
From there, most people recommend turning the nut an additional half-turn to three-quarters of a turn. This "preloads" the hydraulic lifter and keeps everything quiet and functional once the engine gets up to operating temperature.
Method 2: The Running Adjustment (The Old School Way)
If the static method feels too technical, or if you just can't seem to get the "feel" for zero lash with the engine off, you can do it while the engine is running. This is the "old school" way, and it's arguably the most accurate because you're adjusting things exactly as they operate.
First, get the engine up to operating temperature. Pop the valve covers off and put your oil deflectors on the rocker arms. Start the engine back up. It's going to be noisy, and yes, oil will be splashing around a bit.
Go to one rocker arm at a time. Loosen the nut until you hear that specific clicking/clacking sound. Now, slowly tighten it back down until the clicking just barely disappears. That's your zero lash. Once the noise stops, slowly turn the nut another half-turn. You'll notice the engine might stumble for a second as the lifter adjusts—that's normal. Just give it a few seconds to stabilize before moving to the next one.
Common Mistakes to Avoid
The biggest mistake people make is over-tightening. It is very easy to keep spinning the pushrod with your fingers and think, "I still feel a little slack," when in reality, you've already compressed the lifter. Don't rely solely on spinning the pushrod; focus more on the up-and-down movement. As soon as that vertical play is gone, stop.
Another thing to watch out for is worn-out parts. If you're adjusting the valves and you notice a rocker arm that looks blue or purple from heat, or a pushrod tip that's flattened out, stop what you're doing. No amount of adjusting is going to fix a mechanical failure. The Chevy 350 is tough, but it's not invincible.
Pro tip: If you're working on an older engine, check the rocker studs. Sometimes they can "pull" out of the head slightly over the years, making it impossible to keep the valves in adjustment. If you find yourself having to redo the same valve every few weeks, that's likely your culprit.
Wrapping Things Up
Once you've gone through all sixteen valves, it's time to button everything back up. Wipe down the gasket surfaces on the heads one last time with some brake cleaner to ensure a dry, oil-free surface. Install your new gaskets and bolt the valve covers back down. Don't over-torque these! You only need about 4 to 7 foot-pounds of torque; if you crank them down too hard, you'll just warp the covers and cause more leaks.
Give the engine a start and listen. If you did it right, that "sewing machine" noise should be a thing of the past, and your idle should feel much crisper. Adjusting valves on a Chevy 350 isn't just about maintenance; it's about getting to know your engine. There's a certain satisfaction in knowing those internals are humming along perfectly because you took the time to dial them in yourself.
Now, get out of the garage and go for a drive—you've earned it!