General Engine Knowledge



QUESTION : (1) What direction do you turn a distributor to advance the ignition timing?

Opposite direction to the rotation of the distributor.


QUESTION : (2) At what speed does the camshaft turn compared to the crankshaft on a single camshaft engine?

The camshaft turns at ½ the speed of the crankshaft.


QUESTION : (3) Name the 4 different strokes of a 4 stroke engine in order, starting from the stroke that carries air into the cylinder.

Intake stroke…… piston traveling down the bore with inlet valve open.
Compression stroke…… closed valves, piston traveling up the bore.
Power stroke…… closed valves, combustion pushing piston down the bore.
Exhaust stroke…… piston traveling up the bore with exhaust valve open.


QUESTION : (4) What are the three main purposes of glycol in radiator coolant when mixed at between 30% to 70 % by volume?

There are two groups of coolant manufactured for passenger vehicles.
They are simply called type A and type B.
To simplify the difference with the two coolants would be to say that type B coolants are only suitable where aluminum corrosion and hot spot boiling are not a concern. This would make type B unsuitable for use in most post 1980 motor vehicles. Type A coolants give the best protection from hot spot boiling erosion and the inhibitors used are designed to protect a system containing a large amount of aluminum.
The component that controls the hot spot boiling erosion is glycol.So the main reason that type A and type B coolants have different capabilities to control hot spot boiling erosion is the % of glycol used. Almost all type B coolants have very little % of glycol when mixed in their recommended dosages. Types A coolants when mixed will have between 30% to 70% of glycol by volume. This % of glycol is required in the cooling system before any hot spot boiling protection is given.
Hot spot boiling occurs in isolated areas in an engine where the casting is thin and the temperature transfer high, such as the exhaust port waterways. Glycol’s effect on these problem areas is to decrease the erosive action by reducing the size of the oxygen bubbles formed at these hot spots.
Glycol in type A coolants also acts as an anti-freeze. So glycol increases the boiling point and also lowers the freezing point of the coolant.


QUESTION : (5) What action causes a wet liner in a diesel to suffer from erosion?

Cavitation Erosion.

This is caused by the entrapment of tiny air bubbles in the cooling system and their subsequent action on the liner. The tiny vapour bubbles are formed by the mechanical vibrations caused by combustion and the action of the piston slapping against the bore. The action of the vapour bubbles imploding against the inside of the liner cause cavitation erosion.


QUESTION : (6) What position on the diesel wet liner is more likely to show evidence of erosion?

The erosion is predominately on the thrust side of the liner.

This condition is again caused by the implosion of small oxygen bubbles on the cylinder walls. The difference in diesels is that the bubbles are formed by the violent action of diesel combustion.( similar to the bubbles that form in a drum of water if you were to bang on the side of the drum with a hammer.) This diesel liner erosion has the appearance of a multitude of small holes in a concentrated area.
Even with the use of the correct heavy duty coolant, the aggressiveness of this type of erosion necessitates the repositioning of the liner at service intervals. The erosion is predominately on the thrust side of the liner. If the wet liner is operated in the same position for long enough the erosion will eventually form a hole into the cylinder with disastrous results.(hydraulic bending of the con rod and severe overheating)


QUESTION : (7) What side is the thrust side of a cylinder in an engine that turns clockwise if you are looking from the front?

The left side

The crankshaft is powered to the right or from 12 o’clock to 6 o’clock clockwise as combustion forces the piston down and across to the left


QUESTION : (8) What three common methods are used to drive a camshaft?

Gear driven…… chain driven…… belt driven


QUESTION : (9) When repairing an engine and a single piston has to be renewed out of a set, what 5 important points must be addressed?

Weight…… new piston has to be a balanced weight to the other pistons.
Size…… piston to bore clearance has to be maintained.(some manufacturers have graded pistons allowing choice to correct piston to bore clearance) compression
Height…… some engines have pistons with different compression heights for different model vehicles.(e.g. Industrial or passenger car engine)
Crown type…… the same engine used in different models often has different shape piston crowns. (e.g. naturally aspirated or turbo, super or unleaded)
Pin size…… often engines that are used in passenger cars and also in industrial applications may have different pin sizes for each application. Engine types can also have upgrades if the engine has been produced over a long period.



QUESTION : (10) What method is necessary to final wash a re-honed bore?

Always wash the bores with hot soapy water. (test cleanliness with white oiled rag rubbed up and down the bores). This process is best achieved using a soft brush.(bottle type brush).

The reason for using hot soapy water is that no other method removes the abrasive residue left in the hone finish on a cylinder bore.Some times the bore has to be washed several times before an acceptable standard is achieved. The method of checking this standard is to rub a clean oiled white rag up all the bores. The rag must have no trace of black hone residue before the bore can be called clean.
Another area that is mistakenly neglected is the inside of the crankcase area. this area is very rough cast finished and tends to trap the honing abrasive residue. This area should also be rechecked with the white rag test to ensure a complete clean. Again the block should be blown off with air giving special attention to the tapped threads. All machined surfaces should be protected from surface rust by the application of a rust inhibitor. (e.g. RP7)


QUESTION : (11) What jingle is used as a general rule to determine the direction rings have to be fitted to a piston?

Inner chamfer upward, outer chamfer down, unless otherwise marked


QUESTION : (12) How do you calculate the compression ratio of an engine?

Compression ratio is the ratio between the total or combined area above the piston at bottom dead centre (BDC.) and the un-swept or combustion area above the piston at top dead centre. (TDC)
To calculate this ratio use this formula: add the swept volume and the un-swept and divide by the un-swept volume. (sw + un-sw) ÷ un-sw = ratio : 1

Swept volume…… is the area through which the piston travels during one stroke. It is calculated by multiplying the area of the cross section of the bore by the length of the stroke.
The formula to calculate the swept volume of one cylinder is: Pi × r × r × stroke = the swept volume of a cylinder. (area of travel of the piston from BDC. To TDC.) or more simply:
3.142 × (½ the bore size) × (½ the bore size) × stroke = sw

Un-swept volume…… is the area above the piston at TDC where combustion takes place. This area is irregular in shape and has to be measured by the use of fluid and a burette. All areas including spark-plug cavity, pre-combustion chambers and compressed head-gasket thickness are included. Convex or concave piston crowns become part of the measurement calculation. No formula can exist for this calculation except to add and subtract the measurements made to parts of the combustion area with the piston at TDC.

Total engine capacity…… Is the measurement of the swept volume of all cylinders in an engine. e.g. a 173 cubic inch Holden red motor is a 6 cylinder with a bore diameter of 3.5 inches and a stroke of 3 inches. Using the same formula as for swept volume, multiply the answer by the number of cylinders. Check the calculation below.

3.142 × (½ the bore size) × (½ the bore size) × stroke × number of cylinders.
So using this formula for a Holden 173 we will re-check it’s stated capacity.
3.142 × (3.5 ÷ 2) × (3.5 ÷ 2) × 3 × 6 = capacity
3.142 × 1.75 × 1.75 × 3 × 6 = 173.2 ci


QUESTION : 13) Super or premium fuel has a higher octane rating than regular fuel, which fuel burns the slowest?

Super / premium fuel burns slower than regular fuel. The higher the octane rating the slower the rate of burn. If you consider this carefully the answer to question (14) becomes very obvious.


QUESTION : (14) If an engine is pinging, would you advance or retard the ignition timing?

Retard the ignition timing.

Pinging is a word used to describe the noise created in an engine when detonation occurs. Detonation is when combustion starts on two flame fronts and collide violently together. (heard as a rattling sound as the throttle is opened)The audible pinging noise is a result of the sudden increase in combustion pressure being reached before the piston is in the correct position to convert it to power. So retarding the timing will move the maximum combustion pressure point to a position where no second flame front spontaneously ignites.


QUESTION : 15) If you had an engine pinging and the ignition timing was set correctly (including the advance curve), what would be the two most obvious things to check as the possible cause?

Compression ratio too high. If the compression ratio is too high the combustion pressure will reach a point where a second flame front spontaneously ignites. As these two flame fronts collide the combustion pressure is abnormally high resulting in the pinging noise. The noise itself is not the problem , it is the resultant damage to rings ,pistons and bearings that warrants the removal of the cause.
Octane rating of fuel too low. Again if the octane rating is too low the ignited flame front burns too fast causing the maximum combustion pressure to be reached at a position where a second spontaneous flame front occurs. As these two flame fronts collide, pinging is evident.


QUESTION : (16) What does air/fuel ratio represent?

Air /fuel ratio is a measurement of the ratio between the available air and the amount of delivered fuel supplied to the combustion chamber. When a ratio of say 15:1 is measured the ratio indicates a lean mixture. (not enough fuel delivered) when a ratio of 12:1 is measured the ratio indicates a rich mixture. (too much fuel is delivered)


QUESTION : (17) What air fuel ratio is required by a petrol engine to achieve perfect combustion?

The ideal air /fuel ratio for petrol engines is 14.7:1.
( that is 14.7 equal portions of available air to 1 equal portion of petrol)


QUESTION : (18) What is the term used to measure combustion quality?

“Lambda.” The perfect combustion is measured at 1 (ONE) lambda. When tuning engines the lambda reading on a exhaust gas-analyser corresponds directly to the air /fuel ratio. As the air fuel ratio is adjusted closer to 14.7 : 1 the lambda reading edges closer to 1 (ONE) lambda.


QUESTION : (19) What two elements make up all fossil fuels?

Carbon and Hydrogen. All fossil fuels are formed out of decayed living matter and the list includes coal, oil and natural gas. Out of crude oil we refine by a method called fractional distillation many products. These products include lubricating oils, diesel, and petrol etc.


QUESTION : (20) What is greater, horsepower measured at the flywheel or at the rear wheels? And why?

Greater horsepower is available at the flywheel than at the rear wheels. Power is consumed when ever it is applied to a any component to perform any action. Power is lost or consumed in the action of the drive train. All driven components use power including alternators, water-pumps, air pumps and fans. The transmission and differential are no exception.


QUESTION : (21) When is manifold vacuum greater, at wide open throttle or at idle?

Manifold vacuum is greater at idle. The pistons operate as a pump to charge up the cylinder with air. If we close the air intake(throttle butterfly) and continue to suck and at the same time exhaust air from the cylinders a vacuum of up to 26 inches of mercury can be created. As soon as the throttle butterfly is opened manifold vacuum lowers as air at atmospheric pressure rushes.



QUESTION : (22) What is the basic difference in operation of a petrol engine and a diesel engine?

The basic difference is the method of ignition of the fuel mixture.
Petrol engines use spark ignition, diesel engines use compression ignition


QUESTION : (23) What does the term “valve- bounce” describe?

Valve bounce is a condition that describes the action of the valve hitting the seat at high revs and bouncing of the seat again before being controlled by the camshaft.
The valve spring is designed to close the valve onto the seat and hold the valve in that position until the action of the camshaft is positioned to open it again. If the spring is below specifications the spring will not keep the valve seated and valve bounce will occur. In modified engines valve springs have to be selected with higher specifications to cope with the higher revs developed by the modified engine. valves can also bounce simply because the engine is being over-revved due to driving conditions. (sustained full throttle operation in lower gears or free revving.)


QUESTION : (24) Why can loose tappets cause valve damage?

Loose tappets cause the valve to seat at a much greater speed than they were designed to.
Camshaft lobe profiles have an opening and closing ramp as part of their design. The purpose of these ramps is to soften the start of the lift of the valve and to soften the end of closing of the valve. If the tappet clearance is wider than designed the valve contacts the valve seat before the cam follower or bucket reaches the closing ramp. This means instead of the valve being eased on to the seat by the action of the closing ramp, seat contact is made while the follower is on the steep profile of the lobe. If left unattended serious valve and seat damage can occur. Valves can become stressed to the point where they snap at the valve neck. Pounded seats, mushroomed tips and tuliped valve heads can also develop from loose tappets over a long term.


QUESTION : (25) Why can tight tappets cause burnt valves?

Tappet clearance is the manufacturers designed dwell time required for the valve to sit firmly on its’ seat dissipating the heat out of the valve head to the water jacket. Exhaust valves in particular suffer from burning if the heat is not allowed to be dissipated out of the valve head during operation. The only opportunity for an exhaust valve to do this is while it is firmly closed on the valve seat. If this dwell time is shortened or the seat pressure reduced exhaust valves will run so hot that they will be burnt or melted away.


QUESTION : (26) Describe the principal behind angle tightening of torque to yield head bolts.

Angle tensioning was introduced to eliminate incorrect tensioning of bolts due to the inconsistent friction forces that are measured by the traditional torque wrench. When angle tensioning is used the effect of friction at the spot face and threads has no effect on the clamping pressure applied to the gasket or component. The tension wrench does not measure clamping pressure, it is only measuring the friction forces created by each bolt as it is tightened. As each bolt can produce uneven friction forces the clamping pressure attained by this traditional method is also uneven. Angle tensioning relies totally on the principal of using a starting point established by a tension wrench that is even for every bolt in the series. The starting point is evenly established by tightening up all the bolts to a very low torque setting where friction is negligible. From that point the bolts are tightened in a series of angle steps. These angle steps ensure all bolts exert even pressure to the component being clamped, irrespective of the friction created during tightening.


QUESTION : (27) What does the term “glazed up bore’s” describe and what causes it?

Light loads on initial run-in will allow combustion to pass by the rings. This escaping combustion burns & oxidises the oil & bore fragments forming a chemical coating on the honed bore. This chemical coating is known as “Glazing” and has the appearance of golden varnish with the original hone finish being very visibly. Once an engine is glazed up it is usually impossible to achieve complete bed-in of rings. The glazed coating prevents the ring to bore contact required to match up or bed-in rings.


QUESTION : (28) What is the clearance between a big-end bearing and the crankshaft referred to as?

Vertical oil clearance.
The calculation is as simple as adding the measurement of two bearing shells to the measurement of the journal and subtracting the total from the tunnel measurement.This will give you the calculated or actual vertical oil clearance.


QUESTION : (29) What causes the problem referred to as “ring spin”?

Ring spin is usually a result of Unidirectional Honing. Ring spin causes severe localised wear at the top or bottom of the bore. It is usually more pronounced at the bottom where less pressure is forced on the rings. This hone pattern moves the ring around the piston during its travel up and down the bore. When the piston ring reaches bottom dead centre little or no pressure is applied to the ring so it can keep turning or spinning while the piston stops to change direction. This problem will cause pre-mature wear and is very easily recognisable upon strip down.



QUESTION : (30) What name is given to compression ring that has the upper face set at an angle and the lower face square?

Trapezoidal rings. This style of ring is found in diesel engines and is sometimes referred to as a half keystone. A full keystone ring is also designed for heavy duty diesel use and is designed with both the upper and lower faces angled. (wedge shape)



QUESTION : (31) The compression ring described in question 30 is used in some diesel engines. Why is it used in preference to a square shaped ring?

Trapezoidal rings were designed to ensure the ring is free in the ring land. Diesel fuel is a dirty fuel that produces a lot of waste carbon and tar. This style of ring was designed to move in the ring land breaking away any carbon keeping the ring free from sticking in the groove.


QUESTION : (32) What general rule can be applied to rings that fit bore size’s 2 inch to 4 inch in regard to minimum “end gap clearance”?

The minimum end gap is calculated using a general rule of .004″ of an inch per inch of bore. (0.1 mm per 25mm of bore) This general rule is fine for bores from 2.5 inches to 4.5 inches. So a 3 inch bore should have a minimum ring gap of .012 of an inch.(0.3mm). Different ring manufacturers use nominal bore size to manufacture their rings and as pistons can vary in size from one manufacturer to another the minimum is often not achieved. Up to 50% above these specifications will usually be acceptable. It is more important not to be under the minimum clearance as ring seizure and breakage will occur as the rings heat up to normal operating temperature. If ring end gap is under minimum and piston to bore clearance is correct the rings should be replaced or the end gaps filed to size.


QUESTION : (33) The most common cause of engine failures due to faulty workmanship arise from loose nuts and bolts. With this fact in mind what policy should be adopted in regard to the fitting of nuts and bolts?

Don’t fit bolts without tensioning immediately.
Tighten all series of bolts evenly in a criss-cross pattern, in 2 or 3 stages.
Lubricate all threads and bolt head contact points. Use tension wrench where necessary. (big ends, mains, head, rockers, flywheel, cam gears etc. etc.)
Use locktite where bolts require safety lock. (cam thrust screws, chain adjusters, oil pick up mount, camgear, etc.)
Never fit sump plug without new washer and tightened. (either tighten or leave out, this applies at any stage from dismantling to final assembly) Setting up should involve the placement and counting of every nut, bolt and washer in an order. All parts should be accounted for before any assembly is attempted. The last thing you want to be doing during assembly is wandering around looking for bits and pieces. This will only lead to frustration and the possibility of mistakes will increase.


QUESTION : (34) Describe how you would fit a dome welsh plug?

When fitting saucer type Welsh plugs such as the camshaft plug in some V8’s. use a solid flat punch to flatten 2/3’s of the dome area in the centre only. Don’t reshape from convex to concave, just go to flat as at this point maximum size and sealing pressure has been achieved. Don’t use the ball of a hammer to butcher the plug into submission as the quality of the seal will be suspect.


QUESTION : (35) What simple rule can be used when selecting the position to adjust valve clearance on the same cylinder?

Adjust the exhaust clearance when the inlet valve just finishes closing.
Adjust the inlet clearance when the exhaust just starts to open.


QUESTION : (36) On a test what visual exhaust smoke indicates worn rings? Name the colour and time of emission?

Blue smoke at constant medium to high revs. Run the engine at medium to high revs with constant throttle opening. If worn rings are the cause the smoke will increase to a set level and will continue at that level for the duration of the test. If the blue smoke disappears a few seconds into this test worn rings are usually eliminated. Always redo the test several times to confirm your observations.


QUESTION : (37) In a diesel engine what is usually indicated by the appearance of white exhaust smoke on cold starts?

White smoke in a diesel usually indicates un-burnt fuel. Low compression can be the reason as insufficient compression heat is created to correctly burn the fuel. Glow plug engines will blow white smoke on cold starts if one or more glow plugs is faulty. Often the glow plugs are ok but the timer is faulty so insufficient heat is introduced from the glow plugs to aid cold starting.


QUESTION : (38) What is the main design difference between a direct injection diesel and an indirect injection diesel?

Direct injection diesels inject the diesel fuel directly onto the piston crown. Most direct injection diesels have a swirl chamber designed into the piston. Due to the high compression required for a direct injection diesel engine to operate diesel noise is usually more pronounce. The higher compression creates more compression heat so the use of glow plugs is not required for cold starts.
Indirect injection diesel engines inject the diesel fuel into a pre- combustion chamber. This chamber has a glow plug that aids the compression heat to assist with cold starts. Indirect injection diesels usually have a lower compression ratio and are much quieter running.


QUESTION : (39) Simply describe the difference between these induction methods (a) normally aspirated. (b) Turbo charged. (c) supercharged.

Normally aspirated…… is totally unassisted and uses manifold vacuum to induct air into the engine. Turbo-charged…… use an exhaust driven turbine to force air under pressure into the intake. The turbo is mounted into the exhaust engine pipe and has a waste gate valve to control the amount of boost. As the air is forced into the cylinder above atmospheric pressure the air is denser giving more available oxygen. This increases the power output of the engine. Super-charged…… uses a belt or gear driven air pump to force air under pressure into the intake. The power advantages due to forcing air into the cylinders from a belt driven pump are much better at low revs than a turbo. This system is more positive than turbo charging and does not suffer the lag problems associated with turbo charging.


QUESTION : (40) What 2 substances in the cooling system are measured with a chemical tester and gas-analyser to indicate a leakage from combustion to water jacket? ( blown head gasket )

CO2 (chemical tester) & Hydrocarbons (exhaust gas analyser)


90% to 100% correct answers indicate a good understanding of engine problems and functions. This web site is full of information that may improve your knowledge and skill.

Disclaimer Agreement

: Every care has been taken in writing this information and procedures, but no responsibility can be excepted for errors, omissions or misuse of this information and procedures. The information available on this site is for your instruction only and cannot be copied for sale, © copyright 2001 UMR Engines