4 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.
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:
(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
Firing order 1-5-3-6-2-4
(3) Valve Rocking/overlap Method:
(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.
Final Words: The video has not been modified to account for the deletion of method #5. Please ignore any references.