Tappet clearance is a space between the top of the stem and the rocker arm. This clearance is also called valve lash. Tappet clearance are necessary to allow for thermal expansion of valve spindle length at working temperature. It also ensures the positive closing of the valve as it wears down. Clearance should be set when the engine is cold and the cam follower is off the cam peak. Amount of clearance should be monitored as excessive and minimal clearance both have adverse effect on normal functioning of engine. Too much clearance means the valves will likely clatter and, over the long term, cause damage to the valves, camshaft lobes or rocker arms. If there's too little valve clearance, the valves won't fully close, causing excessive heat, and the engine will lose power.

1. Valve Tappet Clearance
Ali Raza
Engr.raza.ali@gmail.com
MAN 14V32/40
MAN Ssang Yong 12V 28/32

2. Sequence of PPt
1. What is Tappet?
2. Excessive clearance leads to,
3. Minimal clearance will leads to,
4. How to adjust tappets?
5. Why does an inlet valve have less clearance than an exhaust valve?
6. Why Valve Tappet Clearance important?
7. Valve Tappet Clearance Limits.

3. Tappet clearance is a space between the top of the stem and the
rocker arm. This clearance is also called valve lash.
Tappet clearance are necessary to allow for thermal expansion of
valve spindle length at working temperature.
It also ensures the positive closing of the valve as it wears down.
Clearance should be set when the engine is cold and the cam
follower is off the cam peak.
Amount of clearance should be monitored as excessive and minimal
clearance both have adverse effect on normal functioning of engine.
Valve Tappet Clearance/ What is Tappet?

4. Excessive clearance leads to
1. Valve opens late.
2. Valve closes early.
3. Cylinder head noise will increase due to tapping effect on valve stem tips.
4. Engine fuel consumption will increase due to improper scavenging.
5. In worst case valve stem can bend and valve will not be able to operate, to
open inlet / exhaust port(s).
6. There are chances for more lubricating oil consumption due to temperature
rise within combustion chamber (due to improper scavenging) and valve stem.
7. It will lead to frequent failure of rocker arms and damaging push rod tips.

5. Minimal clearance will leads to
1. Valve will open early and closes late
2. leaking of valve leading to burning of valve seat.
3. Fuel consumption will increase, engine may become unbalanced,
increased in exhaust temperature
4. Compression pressure will also decrease due to leakage.
5. In worst condition, valve may remain open, resulting in loss of
compression pressure burning of exhaust valve
Clearance should be monitored regularly using feeler gauge for
excessive or insufficient clearance

6. How to adjust tappets?
1.Taking all safety precautions
2.Open indicator cock valve.
3.Engage turning device.
4.Open tappet covers.
5.Make sure the piston is on TDC,
I. From the marking on the flywheel
II.From the fuel cam.
III.Push rod should be free. (Both INT & EXH)

7. Step 1 – Insert Feeler Gauge
Before adjusting tappets you should always
refer to the manufacturer’s instructions for the
correct tappet gap clearance setting, and how to
position the tappet for measurement.
Place the feeler gauge between the tappet and
valve stem.
How to adjust tappets?

8. Step 2 – Read Measurement
Read the measurement on the feeler gauge for a
description of the clearance. If you are trying to
set a gap of 0.4mm, (INT) for example, begin
with this gauge.
If the gauge will not go in or loose, the tappet
will require adjusting.
How to adjust tappets?

9. Step 3 – Select Next Size Up
If the gauge enters without resistance, use a
gauge the next size up to make sure the tappet
clearance gap is no larger than required.
Here, for example, the clearance is too large
because the 0.5mm feeler gauge is easily
inserted and so the tappet will require
adjusting..
How to adjust tappets?

10. Step 4 – Adjust Valve
To adjust the valve, place a ring spanner over
the nut and a screwdriver into the tappet.
The nut is used to lock the tappet at the correct
setting.
Loosen the nut just enough to allow adjustment
of the tappet.
How to adjust tappets ?

11. Step 4 – Adjust Valve
Turning the tappet clockwise with the
screwdriver will decrease the clearance
(counter-clockwise to increase clearance if
clearance is too small).
Only a small turn is needed to adjust the
clearance by a few thousandths of an inch or
hundredths of a millimeter.
How to adjust tappets?

12. Why does an inlet valve have less clearance
than an exhaust valve?
The inlet valve has a near constant flow of cool air.
The exhaust valve has a near constant flow of very hot
air.
Therefore the exhaust valve will expand more then the
inlet valve and need more clearance because it will be at
a higher operating temperature.

13. Why Valve Tappet Clearance important
 Too much clearance means the valves will likely clatter
and, over the long term, cause damage to the valves,
camshaft lobes or rocker arms.
 If there's too little valve clearance, the valves won't fully
close, causing excessive heat, and the engine will lose power.

14. Valve Tappet Clearance Limits
MAN 14V32/40 Clearance (new) (mm)
INT 0.2 +0.1
EXH 0.9 +0.1
MAN Ssang Yong 12V 28/32 Clearance (new) (mm)
INT 0.4 +0.1
EXH 0.9+0.1