TT2 - 4 Camshaft Positioning Methods used for Tappet Adjustment

All the following methods describe how and where the camshaft is positioned to enable the tappets to be set., no matter if you have a hydraulic cam or a solid lifter cam. If you are going to set the tappets static then you will use one of these methods to position the camshaft so that the tappets you want to adjust are positioned on the base circle (heel) of the cam lobe.

All tappets are initially adjusted with the engine stationary, solid or hydraulic. There are four positioning methods used depending on the engine type, camshaft specifications (standard, mild, wild or drag), access to crankshaft and difficulty of rotating the engine. The methods are and listed in order of easiest to more difficult.

Distributor rotor method. (by far the simplest if the engine was running previously)
TDC method (always used on diesel engines but works very well on std to wild engines) (only have to turn the engine twice)
Valve rocking/overlap method (used on most standard to fairly wild tune engines and is the most popular) (the engine is turned over by the amount of cylinders. ie. to set a 6cyl the engine is turned over 6 times)
Inlet just closed/exhaust just opening (ICEO) (can be used on all cam profiles)

If you have an overhead camshaft (OHC) engine then positioning the cam may seem so much easier because you can actually see it. But seeing the cam can actually put you off slightly depending which method you are using. Sometimes I tend to ignore that I can see the cam and look at valve movement only.

1) Distributor Rotor direction:

A great method for total beginners as you simply can't go wrong. If the distributor is still in the engine and you know the engine was running then this method is OK to use. Simply remove the distributor cap & follow the rotor button. Align the tip of the rotor up to a HT lead in the cap. That cylinder will be on TDC ready to fire and therefore both valves will be closed and the lifter will be on the base circle of the camshaft. You will be able to adjust both valves.

(2) TDC Method:

This method was reserved for diesels many years ago as they are extremely difficult to turn over due to higher compressions. Nowadays many car manufacturers that still use solid tappet camshafts also have adopted this method for petrol engines. This method only requires you to turn the engine twice. The No.1 cylinder is set on either the overlap of valves on TDC or compression TDC, then half of the valves in the engine are set. The engine is then rotated by 360 deg and returned to TDC and then the remaining valves are set. Fairly simple, all you need to do is observe #1 cyl or its opposite while your turning the engine to the TDC mark. You are looking for the exhaust to be closing & the inlet to start opening. Once that happens line up the timing mark to TDC, you won't be far from it. The other cylinder will be on TDC compression.

Whichever cylinder you start with, ie. if you started with TDC compression #1 which is the blue table below, you will set the tappets according to the instructions within the blue table. Then you will rotate the engine 360 degree & set the tappets according to the orange instructions. If however you started with the orange table then carry out the adjustment on the tappets in the orange section, then rotate the engine 360 degrees and set the tappet to the blue instructions. Regardless of whether the camshaft is driven by a chain or connected to the crank by gears, it does not change which valves need setting from the tables below.

Firing order 1-3-4-2

4 Cyl Engine	No1	No2	No3	No4
TDC compression #1	set In & Ex	Set In	Set Ex	on overlap

TDC compression #4

on overlap

Set Ex

Set In

set In & Ex

Firing order 1-5-3-6-2-4

6 Cyl Engine	No1	No2	No3	No4	No5	No6
TDC compression #1	Set In & Ex	Set In	Set Ex	Set In	Set Ex	on overlap
TDC compression #6	on overlap	Set Ex	Set In	Set Ex	Set In	Set In & Ex

Firing order 1-4-2-6-3-5

6 Cyl Engine	No1	No2	No3	No4	No5	No6
TDC compression #1	Set 1n & Ex	Set Ex	Set In	Set Ex	Set In	on overlap-
TDC compression #6	on overlap	Set In	Set Ex	Set In	Set Ex	Set In & Ex

(3) Valve Rocking/overlap Method:

This describes the action that is happening as the engine is being turned over to a position where you are setting up the first cylinder to adjust the tappets on. In most engines there are always 2 pistons that are at Top Dead Centre (TDC) at the same time. One is beginning the power stroke, commonly known as TDC Firing or compression and the other is beginning the intake stroke commonly referred to as TDC rocking. What you are looking for as you turn the engine over is the valve action of the exhaust valve. It will be closing (coming up) as you continue to turn the engine, when it is almost shut you will notice the inlet start to open (going down).

At this point you stop turning the engine. You have just created the TDC rocking/overlap on this cylinder and have set up the condition required to adjust the tappets on the other cyl that is also on TDC. This cylinder will have both valves shut and the lifters will be on the back side (base circle) of the camshaft in the safe area between the opening & closing ramps of each lobe for that cylinder. You will have clearance between the rocker arms and the valves except of course for hydraulic lifters. The spark plugs should be removed to make it easier to rotate the motor. In a 4 cyl engine you will turn the engine by hand 4 times to adjust all the tappets. In a 6cyl, 6 times and so on.

To make life easy I have constructed a simple sequence table above, you may like to scribble down your firing order on a piece of paper the first time you attempt to do your tappets. A quick demo of how to read it on the 6 cylinder one. 1 & 6 are joined. That means when 1 is on overlap you set 6. When 6 is on overlap you set 1. Simple as. Click on the camera to see a video of how to join the numbers with some more helpful information.

(4) Inlet just Closed Exhaust just Opening. (ICEO)

I have only ever used this twice, once before I was an apprentice and once during my apprenticeship. You work on one tappet at a time. Pick a cylinder and observe the valve movement as you turn the engine slowly. When the inlet valve just shuts, stop and set the exhaust valve clearance on the same cylinder. Continue to rotate the engine until the exhaust valve on this cylinder just starts to open, stop and set the Inlet valve clearance. That's it, go on to the next cylinder and repeat the same process. I did not think this method was that popular but apparently it is used by many. Each to their own. The photos show just where the tappet is on the camshaft when in both positions. This guarantees that the tappet is near in the centre of the base circle where some mechanics believe it should be set, therefore a lot of people believe this is the only way to do it. I am afraid I do not agree with that premise. See if you can work out how many times the engine must be cranked over to set all the tappets, I say no thanks to this one.

Using a cam profile I made years ago, I made a video demonstrating the above four methods, click the car to see it.