Tips for adjusting hydraulic valves

March 1, 2008 | By Richard Prince


I have a 1965 Chevy Impala with a 283 cid engine that has 95,000 miles. I recently tuned it up with new spark plugs, plug wires, distributor cap, ignition rotor, and ignition points. I also cleaned and adjusted the carburetor.

After this my vacuum gauge showed 18-inches hg with mild fluctuations of the needle, indicating that the valves needed to be adjusted. I had previously adjusted them 8000 miles ago. I adjusted

the hydraulic valves by loosening each one until it started clattering, then I tightened it until it stopped clattering.

Then I added one turn in 1/4-turn increments, waiting 10 seconds between each 1/4-turn.

Why did I need to adjust the valves again only 8000 miles after the last adjustment? I thought hydraulic valves didn’t need adjusting.

I’ve been told that I can adjust the valves by loosening them until they clatter, and then tightening down until the noise just stops. After repeating the procedure for all valves, shut down the engine and turn all valves down one full turn. What is your opinion of this procedure?


You don’t say what the vacuum gauge did after the valve adjustment but I’ll assume from what you’ve said that the reading improved and, therefore, an adjustment was warranted.

There are several possible explanations for why you needed to adjust the valves only 8000 miles after your last adjustment.

Assuming you followed the exact same procedure previously, and the engine was at operating temperatures both times, and you were at the same altitude both times (altitude won’t affect the actual valve adjustment but it will impact the vacuum reading so if you used your vacuum gauge to make the adjustment a readjustment may be called for if altitude changes significantly), my best guess for why a readjustment was warranted is that the rocker arm nuts moved a bit. If the nuts and/or studs are worn enough, the nuts can move over time as the engine is running.

Another possibility is that the cam lobes and/or lifters have worn significantly over the 8000 miles since the previous adjustment. You can adjust the valves as you describe, by turning down all of the rocker nuts until clatter stops and then shutting the engine and turning each nut down one additional turn, but I don’t recommend this.

The point of doing it with the engine running and pausing 10 seconds after each 1/4-turn of tightening is to allow the lifters time to adjust so that they don’t keep a valve open past the point in time when it should be open, thus risking contact between the valve and piston.

The best way to adjust each valve is with a vacuum gauge connected.

After all lash is taken up and the clatter stops, turn the nut down to the point where the highest and steadiest vacuum reading is obtained.