TZ Power Engineering

Control and Adjusting of Valve Clearance / Tappet Clearance

TAPPET CLEARANCE

This is the clearance available between the rocker arm tip and valve stem when the valves are closed position & engine at the cooled condition at the compression stroke.

Tappet clearances are necessary to allow for thermal expansion of the valve spindle length at working temperature. When this clearance increases or decreases, there is an adverse effect on the timing of opening and closing of the valve.

* If the clearance increases- The valve will open late and close early.
* If the clearance decreases- The valve will open early and close late.

The general clearances are somewhere between .30mm to 1.5 mm depending on the manufacturer and the valve (Air or Exhaust). A clever engineer will always keep an eye on it and will adjust them timely.

How to take the tappet clearance

Bring the piston to TDC of compression stroke, this will ensure by

* The flywheel marking
* The fuel pump mark
* The checking the camshaft fuel
* The valve cam position.

On this position fuel cam lobe will touch the fuel pump or valve cams will be on base position(off cam position) that means both valves are closed position, at this time push rod will be free this can be check by rotating push rod. and take the clearance between stem and rocker arm tip by using a feeler gauge and adjusted by loosening or tightening the tappet adjusting screw.

Normally we check it by flywheel marking and pushrod. Taking tappet clearance is a skill, same as the adjusting it. First of all, you need to make sure that the unit you are going to take tappet clearance should be at top dead center. This is clearly marked on the flywheel. You can use turning gear to turn that particular unit to TDC. Usually, there are 6-8 units in four stroke engines. So at the same time, the flywheel will show two units at TDC. To make sure that particular unit is on the compression stroke and not at the power stroke, you can turn the push rods of both units by hands to check. The one with free push rods is the one which is at compression stroke and the one with tight push rods is at power stroke. So avoid the one which is at power stroke.
Now you need good feeler gauges of different thickness. Now gently try to push these feeler gauges between the clearance of valve and rocker arm. You may have to try different thickness. Just check in the manufacturer manual as for how much standard clearance should be.

Now you know that your clearance is less or more. But now comes the adjustment part. This is quite important though. You need to open the nut on the rocker arm as shown below. After opening, you can adjust the clearance.

Adjusting of inlet valve clearance;

1. Turn the engine so that the roller, rest on the circular part of the cam, i.e the inlet valves and the exhaust valve are closed.

2. Loose the adjustment screw on the valve brige and rocker arm. See fig 1.

3. Clearance between the valve bridge ang valve spindle depend on your maker's manual.

4. Place the feeler gauge marked with "correct" 0.50 mm above the valve spindle nearest to the rocker arm bracket see fig 1.

5. Adjust the clearance between valve bridge and valve spindle by means of adjustment screw on the rocker arm (above the push rod) and tighten th lock nut.

The feeler gauge is to remain in this position when adjusting the clearance of the other valve.

6. Place another feeler gauge, at the same size 0.50 mm above the other valve spindle, see fig 2.

7. Adjust the clearance between valve bridge and valve spindle by means of the adjustment screw and valve bridge, and tighten the lock nut, see fig 2.

8. Check that the clearance is correct simultaneously at both valve spindles.

Adusting at Exhaust Valve Clearance;

9. Carry out adjustment in yhe same way as describe for the inlet valves, but using the feeler gauge for the exhaust valve clearance 0.90 mm.

10. The feeler gauge for checking the clearance have two gauge which are marjes "incorrect" and "correct", the latter to be used when adjusting the valve clearance, see fig 3.

After tightening up the counter nuts on rocker arms and valves bridge, be sure that the feeler gauges marked "correct" can be inserted into the two clearances simultaneously as where it must not be posible to insert the gauges marked "incorrect".

Note:
Keep the feeler gauge all the time between them, to get the perfect clearance.

Tip:
When you move feeler gauges while adjusting for particular clearance, you should be able to slide it smoothly (not too tight and not too loose). After adjustment, tight the nut with given torque. Keep the record for future use. Hope this will be useful for you.

EXCESSIVE TAPPET CLEARANCE
will cause the valve to open late and close early in the cycle and will reduce maximum lift it will also noise and get damage from the impact of the working surface.

LESS CLEARANCE
will cause the valve to open early and close late with increased maximum lift it may prevent the valve from closing completely as it expands this may cause valve burning and low compression.

Fuel Injection Pump for DAIHATSU DIESEL ENGINE DC-17