Tech Reference Page #17

Adjusting Valves

Authored by Wes Vann, revised September 29, 1998

Big disclaimer!

This page covers a subject (process) that I've resisted writing on due to not wanting to give misleading information. I've had my problems (heck, I'm human!) and didn't want to tell others what to do if I wasn't comfortable with the procedure or wording. I highly recommend that you purchase the book "how to rebuild your SMALL-BLOCK CHEVY " by David Vizard!

I don't plan to go into cam design or make recommendations! Not now, not ever!

THE FIRST BIG IMPORTANT NOTE;

The recommended amount of "preload" adjustment that I've seen in various places goes from 1/4 turn to a full (360) turn. On this page, it's written as 1/4 turn and I feel that this is a "safe" adjustment. If I ever manage to find the definitive source, I'll quote what they say. (Does God adjust his valves, or is it just allocated to some angel? Then again, I'll bet he has a solid lifter, high compression big block.)

THE SECOND "BIG IMPORTANT NOTE";

There was a problem in how the paper was originally written due to my "small block" thinking. John Scavelli pointed out to me that my numbering of valves from "front to back" wasn't really correct due to the fact that on a big block, the order is different. That fact has to kept in mind and I'm going to try to clean up the wording. My thanks go out to John!

THE THIRD "BIG IMPORTANT NOTE";

It was pointed out by Bill Koustenis (Advanced Automotive Machine) that on a radical cam with an excessive amount of valve overlap, the stated procedures may not be totally correct. This is due to the lifter not being on the base circle at the time you are adjusting it. If you are going to be installing some sort of extreme cam, it's recommended that you get a "recommended procedure" from the cam manufacturer. Don't just ask the guy behind the counter at Pep Boys! Use your head and question anything that may seem odd!

Concepts and terms;

Base circle; This is the low point of the cam. The lifters have to be on the base circle at the time that you are adjusting the valves! Almost 3/4 of the cam profile is "base circle".

"Bleed Down"; As the cam lobe pushes upward on the lifter, it forces the oil inside into more compression (pressure) than what the engine is supplying. As a result, a small amount of oil is forced out of the lifter and back into the engines main oil gallery. There are SMALL holes inside the lifter that limit how fast the oil can escape. This is pretty much a standard resistance (to bleed down) except for lifters like those sold by "Rhoads".

Clockwise rotation; It's dumb, but I have to add all the little things! When I talk about rotating the engine clockwise, I'm talking about as if you are standing at the radiator looking at the engine. (it would be opposite if you thought about it as if sitting in the drivers seat) Clockwise rotation is the direction that the engine rotates when it runs. I rotate the engine by putting a socket on the harmonic balancer nut and use a large ratchet wrench (really, it's a breaker bar).

Cam Lobe; This is the area of the cam above the base circle. The lift of the cam is the height of the lobe measured off the base circle. (This is kind of interesting, if they regrind a cam to get more "lift", in reality, they are just making the base circle smaller! Otherwise, they would have to add material to the lobe. Not done!)

Hydraulic Lifters; This is going to cover the adjustment of hydraulic lifters. The lifters run on the cam and work the push-rods. Hydraulic lifters are "kind of" self adjusting. It's only within a certain range and you have to get them close. A hydraulic lifter has four parts; the body, the plunger, small (internal) spring, and a retaining clip. (don't take one apart, just trust me!) If you look at the side of one, you will notice that there is a small hole. It's through this hole that oil is fed under pressure!

Numbering;

The firing order on production Chevy V8 engines (both big block and small block) is 1-8-4-3-6-5-7-2.

The pistons (or cylinders) are numbered 1,3,5,7 on the drivers side, starting closest to the radiator. On the shotgun side, they are 2,4,6,8.

On a small block, the valves are; exhaust, intake, intake, exhaust, exhaust, intake, intake, exhaust. This is true for both sides!

On a big block, the valves on the drivers side (starting at the one closest to the radiator) are exhaust, intake, exhaust, intake, exhaust, intake, exhaust, intake. On the shotgun side, they are intake, exhaust, intake, exhaust, intake, exhaust, intake, exhaust.

Pivot Balls; I may be using the wrong term here, but this is what I consider it. It's the half sphere that the rockers pivot on. On some rocker configurations, there may be a pivot shaft. Some of the pivot balls that came from the factory had grooves in them that helped keep the surface oil in place. You can't tell without pulling the ball off and looking at it.

"Pump up"; This is the action of the lifter filling with oil. If there is a blockage in the oil lines (or the hole in the side of the lifter), it will never pump up and the internal plunger will bottom out inside the lifter body. There is some disagreement in what I consider "pumped up". In my mind, a lifter is only pumped up while there is oil pressure in the engine and this is only while it's running!

Rockers; This is the connection between the push-rods and the top of the valves. As the push-rod goes up, the rocker pushes the valve down (open). Small block Chevy rockers have a ratio of 1 to 1.5. This means that the valve moves 1.5 times the distance that the push-rod moves. (high lift rockers are something like 1 to 1.6) The accuracy of the factory units isn't all that great and it's not that uncommon to "select" a matching set if blueprinting an engine..

TDC; Top dead center. It's always (?) referred to in relationship to the number one piston. Keep in mind that we are talking a 4 stroke engine here and that TDC occurs TWICE for everytime that the spark fires.

Preliminary stuff

This is going to be written as if the distributor isn't installed, or may be in wrong. It assumes that the timing chain and gears are correct.

Disconnect the battery!

Remove the valve covers and the spark plugs.

You will have to make some marks on the harmonic balancer. Start with the TDC mark that is already on it and make marks 90 degrees apart. In other words, make a mark directly across from the TDC mark and then marks halfway between that point and TDC mark.

You have to start with the engine at TDC, at the cycle where number one spark plug would fire. In order to do this (don't forget that there are two TDC's) you have to rotate the engine and watch the number 1 intake valve (second from the front on the drivers side). You want the TDC that happens right AFTER the intake valve has opened and closed.

How's it done----Method #1;

You are now at TDC (at the end of the compression cycle) and are ready to adjust some valves. With the cam in this position, the valves for the number 1 piston are fully closed. Another way to say this is that the lifters for the number 1 cylinder are on the base circle.

When you adjust the valves, don't use a deep socket! By using a standard socket, the socket shouldn't touch the pivot ball. If it does touch the ball, it is harder to get a accurate feel.

Adjust the #1 cylinders valves;

You want to hold the push-rod and notice that it's loose (or at least should be at this point). As you adjust the rocker down, you will remove the slop. You now want to tighten it down an additional 1/4 turn.

Yes, it's that simple. Except you have to keep in mind what you are doing. The idea is that you are tightening everything down just until the slop is gone. If you read instructions wrong and adjust down until you can't rotate the push-rod with your fingers, you have compressed the internals of the lifter and bottomed out it's plunger. If you then go that additional 1/4 turn, the valves are ALWAYS open and the engine will not start. (this is a BTDT item)!

You want to adjust both of the valves for the cylinder in question.