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5 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 five 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.

  1. Distributor rotor method. (by far the simplest if the engine was running previously)
  2. TDC method (always used on diesel engines but works very well on std to wild engines) (only have to turn the engine twice)
  3. 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)
  4. Inlet just closed/exhaust just opening (ICEO) (can be used on all cam profiles)
  5. Max lift + 360 crank degrees. (the most crank turning intensive)

Before I look at describing all the positioning methods, I also made a clip to show how to draw the inlet and exhaust cam lobes for one cylinder. The video is in the Engine section under the Camshafts button. It may help you to visualise the camshaft lobes. Then I test drive it by rotating the drawing explaining what is happening to valve movement during each stroke of the engine. All the following 8 videos on this page use this drawing to show you where the cam lobes are positioned for each method.

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. If you adopt the same then you can set-up your cam position exactly as the videos show and get the same result. Sit back grab some pop-corn & soft drink and enjoy the show.

 


1) Distributor Rotor direction:

A great method for total beginner 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.


(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 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 and you don't have to watch what the valves are doing. The video has more details on determining which cylinder is on compression when the valves were not observed during rotation of the engine to TDC.

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 instructions given and then rotate the engine 360 degrees and set the tappet to the blue instructions.

Firing order 1-3-4-2

4 Cyl Engine

No1

No2

No3

No4

TDC compression #1

set In & Ex

Set In

Set Ex

-

TDC compression #4

-

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

-

TDC compression #6

-

Set Ex

Set In

Set Ex

Set In

Set In & Ex

Firing order 1-8-4-3-6-5-7-2.   Small Block Chev

8 Cyl Engine

No1

No2

No3

No4

No5

No6

No 7

No 8

TDC compression #1

Set In & Ex

Set In

Set Ex

Set Ex

Set In

-

Set In

Set Ex

TDC compression #6

-

Set Ex

Set In

Set In

Set Ex

Set In & Ex

Set Ex

Set In

Firing Order 1-2-7-8-4-5-6-3.   Holden 253 -308

8 Cyl Engine

No1

No2

No3

No4

No5

No6

No 7

No 8

TDC compression #1

Set In & Ex

Set Ex

Set In

-

Set In

Set In

Set Ex

Set Ex

TDC compression #6

-

Set In

Set Ex

Set In & Ex

Set Ex

Set Ex

Set In

Set In

Firing order 1-5-4-2-6-3-7-8.   Ford Windsor

8 Cyl Engine

No1

No2

No3

No4

No5

No6

No 7

No 8

TDC compression #1

Set In & Ex

Set Ex

Set In

Set Ex

Set Ex

-

Set In

Set In

TDC compression #6

-

Set In

Set Ex

Set In

Set In

Set In & Ex

Set Ex

Set Ex

Firing order 1-3-7-2-6-5-4-8.  Ford 302 & 351 Clevland, also 351 Windsor

8 Cyl Engine

No1

No2

No3

No4

No5

No6

No 7

No 8

TDC compression #1

Set In & Ex

Set Ex

Set Ex

Set In

Set In

-

Set Ex

Set In

TDC compression #6

-

Set In

Set In

Set Ex

Set Ex

Set In & Ex

Set In

Set Ex

All of the tables above are derived from the camshaft drawing by simply placing the lobes on the base circle for the No.1 cylinder or overlap if you wish and working backwards to determine the position of the camshaft lobes for all other cylinders at that point of time. The only precaution here is that the timing mark on the front pulley must be accurate.


(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 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.  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. Then you can cross them off as you do them or to see how to join the numbers click the video.

 


(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 cylinder 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. The video shows it more clearly. 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.


(5) Max lift + 360 crank degrees:

Not worth wasting more than a line of text on, see the video instead or maybe not.    


Final Words: