INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIACO-CURRICULAR ACTIVITIES CENTER

CCAS 3382 - AUTOSKILL 2

:: VALVE SETTING ::

Introduction

Valves are used in most piston engines to open and close the intake and exhaust ports. Valves are

round in shape for mechanical reasons, among which are self-aligning, easy manufacture and have the ability

to rotate without compromising sealing. Since the valve stem extends into lubrication in the cam chamber, it

must be sealed against blow-by to prevent cylinder gases from escaping into the mechanical part of the

engine.

Modern internal combustion engines are using either four-stroke, two-stroke or six-stroke cycle

with spark ignition and compression ignition, use poppet valves to allow air to flow through the cylinder

head cylinder and exhaust gases out. The earliest engines used alternative valve types such as D slide valves

that proved to be unsatisfactory, especially at higher speeds. The actuation of these valves is the subject at

hand.

Some automobile engines use more than one inlet and/or exhaust valve to reduce individual

reciprocating mass for separate valves. For a given valve lift it also increases open passage area, improving

power to the engine. F1 racing car engines use pneumatic valve springs with compressed gas rather than

metal springs to close their valves because it have faster response through lower mass than metal springs and

thereby allowing greater engine speed.

For instance,

• a properly running engine needs exact valve clearance

• If the intake or exhaust valves are not sealing properly, result in a leak during compression.

• What you are doing is adjusting the clearance between the rocker arms and valve stems

Name of parts and components

Hand Tools:

19mm socket & Rachet handle

12mm open common ring spanner

Screwdrivers, flat-blade -- medium and large

Feeler gauge blade with a 0.25" intake & 0.30” exhaust

Functions and Working Systems

Nowadays, internal combustion engines in cars, trucks, motorcycles, construction machinery and

many others most commonly use a four-stroke cycle. The four strokes refer to intake, compression, and

combustion and exhaust strokes that occur during two crankshaft rotations per working cycle of Otto Cycle

and Diesel engines. The four steps in this cycle are often informally referred to as "suck, squeeze, bang, and

blow."

The cycle begins at top dead center (TDC), when the piston is the furthest away from the crankshaft.

On the first stroke (intake/induction) of the piston, as the piston descends it reduces the pressure in the

cylinder, a mixture of fuel and air is forced by atmospheric pressure, into the cylinder through the intake

(inlet) port. The intake (inlet) valve (or valves) then close(s) and the following stroke (compression)

compresses the fuel-air mixture.

The air-fuel mixture is then ignited, usually by a spark plug for a gasoline or Otto cycle engine or by

the heat and pressure of compression for a Diesel cycle or compression ignition engine, at approximately the

top of the compression stroke. The result of expansion of burning gases pushes the piston downward for the

third stroke (power) and in the fourth stroke (exhaust), the piston pushes the products of combustion from the

cylinder through an exhaust valve or valves.

Four-stroke cycle (Otto cycles)

Starting position, intake stroke, and compression stroke.

Ignition of fuel, power stroke, and exhaust stroke.

Valve clearance adjustment

Valve clearance refers to the small gap between valve lifter and valve stem (or rocker arm and valve

stem) that ensures the valve completely closes an expansion joint in the valve train. Most engines have the

valve clearance set by grinding the end of the valve stem during engine assembly, overhead cams not needing

subsequent adjustment. In earlier engines which mostly with push rods and rocker arms used adjustable

tappets or hydraulic tappets to adjust for valve and cam wear. Lack of valve clearance will prevent valve

closure causing leakage and valve damage.

Valve Clearance Measurement

Valve clearance is measured with the valve closed, typically at Top dead centre of the compression

stroke. The tappet will be resting on the heel of the cam lobe. A feeler gauge must pass through the clearance

space. The feeler gauge should fit in and out with a slight drag. If the feeler gauge does not fit in, it means the

clearance is too small. If the blade of the feeler gauge fits in loosely then the clearance is too big.

i. Valve clearance too wide

Too wide valve clearance will cause excessive wear to the camshaft and valve lifter contact areas, the

pushrods can also bend and the engine will be making much noise. If the clearance becomes wide enough,

valve timings will change and results in poor performance.

ii. Valve clearance too narrow

A narrow valve clearance will not allow heat expansion and result in the failure of the valve to close

on its seat. The combustion chamber will not seal properly, producing poor compression and power. It is also

possible that the valve can become hot enough to melt.

Valve Adjustment Procedure

1. Valves can be set on a hot or cold engine. A cold engine is a lot more comfortable to work on. Major

camshaft manufacturers recommend setting valves cold, to avoid erroneous adjustments on lifters that

may be "pumped up" If you are setting valves on a fresh engine that has not been run, everything

should be well lubricated before you begin.

2. Remove valve covers, timing belt cover and remove the spark plugs to make the engine easier to turn

over.

3. Turn the crankshaft pulley at the correct point [ T -- ]. Also make sure that camshaft shown at

[ > < ] by using a ratchet handle or breaker bar attached to the crank bolt (size ’19), turn the engine

over in the clockwise direction.

4. At this point, only adjust 6pcs valves which start by 3pcs from cylinder 1, 2pcs from cylinder 2 and

1pc from cylinder 3.

5. Use Open ring spanner + Screwdriver + filler guage to adjust the valve clearance. Adjust 25mm for

intake valve and 30mm for exhaust valve.

6. While holding the adjusting bolt in place with the screwdriver, tighten the lock nut. (The screwdriver

is running through the box end (ring end) of the wrench (spanner) as you do this.) This process is

tricky, so take your time. The bolt will sometimes try to tighten up as you tighten the locking nut, so

it's best to hold it with the screwdriver while you tighten the nut.

7. To complete another 6pcs valve need to turn the crankshaft for 1 clockwise rotation. Then apply same

procedures as step before. Re-check the clearance to make sure tightening it hasn't changed the

adjustment. Repeat the process if necessary (time and patience are important here).

8. Re-install your valve covers and your valve adjustment procedure is finished

Problems

Lack of compression

If the charge of air and fuel cannot be compressed properly, the combustion process will not work like it

should. Lack of compression might occur for these reasons:

Your piston rings are worn (allowing air/fuel to leak past the piston during compression).

The intake or exhaust valves are not sealing properly, again allowing a leak during compression.

Incorrectly adjusted valves can cause the engine to stall.

Too tight, and they don't seal/seat down properly, so that cylinder isn't working hard enough and will

eventually burn that valve.

Too loose and the valve timing changes, so the engine sounds rattly and runs rough.

i. Poor running engine and low performance

iii. Burnt exhaust valve(s)

iv. Broken valve train components (springs, pushrods, lifters, camshaft)

v. Limited lifespan of valve train components

vi. Excessive valve guide and seat wear

vii. Blown up engine

REFERENCES

Http://en.wikipedia.org/wiki/car

Http://howstuffwork.com

http://vwtrends.com