Entries Tagged 'Maintenance & Knowhow' ↓

Preamble
Ever since the first single-cylinder petrol engine driven Car appeared on the roads during late 19th century, a ‘Carburettor’ became synonymous with it. Later on with the advent of multi-cylinder Engines, so did the ‘Distributor’ or ‘Delco’s.

During the last Century, both evolved considerably – till the ‘Euro-II’ like Pollution Norms got the better of them. For, the Carbs worked on a fundamental principle of ‘reaction’, which could easily get stifled for many reasons. Whereas man, wanted to be literally in the Driver’s Seat – as always.

And thus, as the cliché of necessity being the mother of invention goes, a System of ‘controlled-feeding’ of Fuel + Air + Ignition Spark to the ICE Cylinders in the early ‘80s evolved. A ‘system’ like that had to be based on the engine’s ‘needs of the moment’, such as the load on it, its rpm, vehicle’s road speed etc.

Such a ‘system’ had to ensure that the ‘ob-Nox-ious’ Pollutants were kept to a bare minimum all over it’s operating range – not to mention squeezing the maximum ‘mileage’ out of the last drop of fuel that went into it. Thus ‘fuel-injection’ systems were born – replacing nearly a century old Carburettors.

For the uninitiated, ‘MPFi’ stands for ‘Multi point fuel injection’. Such a system ‘injects’ fuel into individual cylinders, based on commands from the ‘on board engine management system’ Computer – popularly known as the Engine Control Unit or the ECU.

MPFi Systems can either be: a) ‘Sequential’ i.e. direct injection into individual cylinders against their suction strokes, or b) ‘Simultaneous’ i.e. together or all the four or whatever the number of cylinders, or c) ‘Group’ i.e. into Cylinder-Pairs.

These techniques result not only in better ‘power balance’ amongst the cylinders but also in higher output from each one of them, along with faster throttle response.

Of these variants of MPFi, ‘Sequential’ is the best from the above considerations of power balance/output.

‘SEFi’’, as advertised by Ford, stands for ‘Sequential Electronic Fuel Injection’, which technically is the best of the above variants of ‘MPFi’. Hyundai/Maruti ‘MPFi’ systems are in fact ‘SEFi’ too. The erstwhile Cielo’s and Matiz’s had the (b) or (c) variants of above MPFi systems.

On the other hand, older Opel-Astra’s had a ’single point’ fuel injection system, which is in between an Mpfi and the now obsolete Single-Carburettor systems.

The ‘Fuel Injectors’ are precision built ‘Solenoid Valves’, something like Washing Machine Water inlet Valves. These have either single or multiple ‘Orifices’ which ‘spray’ fuel into the Fuel inlet manifold of a Cylinder upon actuation, from a common Rail/Header pressurised to around 3 bar, fed by a high pressure electrically driven fuel pump inside the Petrol tank of the Car.

The ‘on-board’ ECU primarily controls the Ignition Timing and quantity of fuel to be injected. The latter is achieved by means of controlling the ‘duration’ for which the Injector solenoid valve coil is kept energized – popularly known as the ‘pulse-width’.

In general, an ECU in turn is controlled by the ‘data input’ from a set of ‘SENSORS’ located all over the Engine and its Auxiliaries. These detect the various ‘operating states’ of the Engine and the performance desired out of it. Such Sensors constantly monitor: 1. Ambient Air Temperature, 2. Engine/Coolant Temp., 3. Exhaust/manifold temp., 4. Exhaust ‘O2’ content, 5. Inlet manifold vacuum, 6. Throttle position, 7. Engine rpm, 8. Vehicle road speed, 9. Crankshaft position, 10. Camshaft position, etc.

Based on a ‘programmed’ interpretation of all this input data, the ECU gives the various ‘commands’ to the Engine’s fuel intake and spark ignition timing systems, to deliver an overall satisfactory performance of the Engine from start to shut down, including ‘emission control’.

This/Part-1 of a 4-part Article is an attempt to familiarise the average ‘BS-II/III’ Car Owner as to what actually lies beneath their Bonnets. In Part-2, we’ll talk about the do’s and don’ts relating to MPFi Cars. In Part-3, for the more curious ones, we’ll see how the stuff works and in Part-4, we’ll explore the commonly encountered problems and DIY-Trouble Shooting.

Immediately, to get the best out of an MPFi System, one should always use – a) The OE recommended Petrol Additives with the ‘Regular’ Unleaded or the new generation ‘Premium’ Petrol’s and b) NEVER Tamper with the OE Wiring Harness of the Car – EVEN to install the ubiquitous Music System OR any other Electrical Accessory - other than those ‘approved’ by the OEM/Dealer and ‘installed’ by him, as these are designed to suit the Car’s OE Central Wiring Harness ‘Couplers’ provided for the purpose. ‘BUTCHERING’ OF THE OE-CWH IS AN ABSOLUTE TABOO FOR MPFi CARS.

Preamble:
In the 12th March article, if not most, some of you may have read about the interesting facts behind AirCraft Tyres. We even invited Readers to answer at the end, as to what makes an ACT burst at take-off, as distinctly different than a more probable one during landing. However, there was hardly any response – barring one and that too not entirely correct.

So yours truly again e-picked the brains of his TyreGuru – Mr. Sudershan Gusain – and this is how he enlightened me…

Tyre burst or explosion, two different things tho’, is an interesting topic and internationally, very few studies have been made in this direction. Here are some general explanations about them and they apply equally to automotive as well as ACTs:

A tyre burst/explosion is not so common a phenomenon but:
• It is difficult to detect before it happens.
• It may have multiple causes.
• It can have tragic consequences.

Some figures from Canada indicate that tyre explosions account for 1% of all accidents leading to deaths over there.

Before we proceed further, we should distinguish a BURST from an EXPLOSION:

BURST
A Tyre Burst can be defined as due to ‘mechanical deterioration’ of tyre material, thus weakening its ‘structure’, resulting in a sudden and violent release of the air.

The causes of a tyre burst can be classified into 2 categories:

MECHANICAL CAUSES
• Excessive tyre inflation.
• Improper bead seating on the Rim.
• Structural fatigue of the casing.

CHEMICAL CAUSES
HEAT is the main cause that can lead to a burst of chemical origin. Various chemical reactions can happen when heat inside the tyre builds up. Thermal decomposition of rubber then occurs and it chemically breaks the tyre material into its original components viz oil, gas and char.

EXPLOSION
Explosion is a sudden expansion of a gas under pressure. Flammable gases with relatively low self-ignition temperatures can get formed inside a tyre due to heat and/or decomposition of tyre material due to many other causes. And when the internal temperature of a tyre becomes higher than the self-ignition temperature of such gases, an ‘explosion’ can occur. However, for it to happen, the following conditions are to be met:
• Concentration of enough inflammable gas.
• Inside tyre temperature higher than the self-ignition temperature of the gases formed within.
• Oxygen concentration inside the tyre higher than 5.5%.

A chemical explosion of such a nature is much more violent than a burst, as it occurs at much higher pressures - usually ~ 500psi or more.

For a tyre explosion to occur, a high degree of heat is required. The causes of such high heat generation are due to following possibilities:

The most common cause is ‘wheel welding’. Rubber will start to decompose around 250°C. With the increase in internal temperature, the mix of oxygen and flammable gas auto-ignites at around 450°C and an Explosion can occur.

Use of a welding torch to release bolt/nut.

Use of petroleum lubricant or solvent during tyre mounting.

Brakes’ overheat.

Electric discharge either from a high voltage line or lightning.

Fire in ambience.

Severe under inflation or overloading.

Presence of contaminants inside the tyre.

Oil or other combustible fluid ‘absorbed’ by the tire.

If we now go back to the original question i.e. Tyre burst or explosion during take-off, one can probably understand that we should first determine whether it is a burst or an explosion. They key causes in case of an aircraft would be:

These are also the reasons why ‘Nitrogen’ inflation as well as disc brakes is mandatory on Aircrafts.

Preamble
As is not unusual, the last week’s Article on the Life Cycle of an Automobile Engine evoked some pertinent questions from one of the regular e-readers of this column. I won’t be surprised if most of you had similar reactions. So this is how it went…

Question
Just went through your article on ‘Engine life’ and was curious about the line ‘Maximum dry CR 13.5 kg/cm @ 400 rpm’. I assume ‘dry’ means cranking the engine without allowing ignition to take place and ‘CR’ means compression ratio, but what does the figure 13.5 kg/cm stand for? Is it pressure (i.e. kg/sq. cm)? VG/Mumbai

Answer
‘Compression’ Tests are of 2-types - i) ‘Dry’ meaning as done below and - ii) ‘Wet’ meaning after injecting a 10-20 ml of engine oil thro’ the spark plug opening ‘before’ cranking the engine for the test. Ideally speaking, in a healthy engine, there shldn’t be much difference between the two. However, if the piston/rings are worn out, there will be significant difference. So a ‘wet’ test is a sort of double check before concluding that the p/r’s are gone.

It’s a std procedure when taking the ‘compression’ readings to - i) remove all the spark plugs/Air Filters, ii) depress the Accl Pedal fully and iii) crank the engine by the starter motor, which is usually 400 rpm per typical petrol engine starter motor design, till the pressure gauge screwed in place of a spark plug/cyl registers a max reading (2-fellows needed). The PG used is a ‘Stay-Put’ type, like a Tyre Pressure Gauge, which permits one to read it accurately and then ‘reset’ to zero.

The fig ‘13.5′ is - i) the ‘pressure’, either in psi or kg/cmsq here, recorded by the PG used as above and ii) ‘13.5′ is the fig for a healthy engine having a compression ratio of 9:1 - as per Suzuki Work Shop Manuals.

Question
Also, would the pressure not depend on the compression ratio, as well as the inlet pressure (in supercharged/turbocharged engines, this would be above atmospheric).

Answer
Obviously it’ll be higher for engines having ‘Compression Ratio’ higher than 9:1. At 400 rpm, atleast a Turbo Charger will have no effect coz the engine is prevented from firing by removal of its Spark Plugs and in a Super-Charged engine, the pressure build-up will be negligible at such a low rpm. May be they recommend taking off the S-C drive belt in such a case but I won’t know off hand as I’ve yet to come across a work shop manual an S-C car!

Question
Wouldn’t it also not depend on the condition of the air filter and the inlet/exhaust valves (more the fouling, less the pressure)?

Answer
As I’ve said above, the air filter is removed for such a test. I suppose valve/seat wear goes hand in hand with piston/rings wear, as far as an engine performance is concerned.

Subsequent Responses
Thanks for the very precise answers to my queries! It has improved my understanding of automobile engines. I remember I had the chance to witness a ‘dry’ test, after the garage had done a ‘carbon clean’ chemical process on my Maruti-800 a few years back.

However, instead of the ’stay-put type’ pressure gauge you mentioned, they had an instrument that took the compression readings on ‘cards’, much like an engine indicator (used in marine engines). He claimed that the improvement in readings was due to the ‘carbon cleaning’ of the valves/valve seats and pistons/rings. He even inserted a sort of probe inside the spark plug hole, to show me on a video screen the cleaned insides - an instrument similar to what ENT Doctors use to look inside one’s ears/throat! VG.

That was an interesting experience you shared with me VG. However, this ‘Carbon-Clean’ using machines for the purpose can be dicey and do more harm than good, as certain minimum carbon deposits at ‘strategic’ locations within an engine are actually necessary, to enable it achieve its highest possible/designed compression ratio. SKG.

Preamble
I’m often asked what’d be the estimated life of a car engine, say an M800 or for that matter even a Honda City. Needless to say I find myself at a loss for words when pitted against such ones. Sample the following QnA that had with a fairly knowledgeable guy…

Question
What’s the funda for an ICE’s life i.e. how much should I expect a used Honda 1.3 DX engine to last - given that it shows 42 Kkm on the odo as of now. I have heard that 1-Grand Mark is the near end of a Car engine and time for an overhaul. Would that mean I only have another 58 Kkm or so to see before I have to visit the garage for an expensive overhaul? Or does it also depend on the way one drives and maintains the engine??

Answer
A question like this is difficult to answer with reasonable accuracy. It’s some what like asking why some Guys croak at 30 and some > 75, when the average life expectancy in India is 50!

For example, I have seen any # of M800s in DLH with engines killed by 70 kkm whereas I had a ‘91 std with a Retrofit AC, driven by atleast 6-members of the family over a period of 10 yrs/144 Kkm, with engine still in full pep/nil oil consumption – to the extent none could figure out that the odo had once turned over!

For starters, consider the following extract from my Article ‘Funda’s of Automobile Engg.’

Q: What is Engine Life Factor (ELF)? How can it be calculated?

A: It’s a ‘Factor’ given by the Formula ‘ELF = 100,000/Max RPM x Compression Ratio’ of an ICE. Since it’s a ‘number’ only, it’s devised to ‘compare’ the Life and Reliability amongst comparable ICEs.

Now where does that leave one - gasping for breath or waiting to exhale!?

On the other hand, it’s been my experience, based on funda’s of A-E, that the life of a Car Engine largely depends on the following - perhaps in that order:

1) Its basic design/materials, ‘workmanship’, and OEM-QC standards.
2) How well mated it’s to the Car by way of ‘Power to Weight Ratio’ - anything below 70 is an ‘edge’ design.
3) The proverbial ‘nut behind the wheel’.
4) How well it’s been ‘run-in’ and subsequently driven/serviced/oil-changed.
5) How often and for how long it’s been driven at >75% of its max rating - rpm/bhp. Cars in India lose out on this front compared to their western counterparts that log most of their mileage in 5th gear a/a ours in 3rd - typically translating to 1.66:1 ELF wise!

It’s my reckoning that OE Engines of most present day cars with PWRs > 70 can easily do 200 Kkm+ if ‘well looked after’. However, when it comes to assessing the ‘residual life’ of a used car engine, one can go about it scientifically as follows:

A typical expression found in various W/S Manuals in respect of the ‘health’ of a 9:1 Compression Ratio (87 Octane) Petrol Engine states:

i) Max ‘dry’ CR - 13.5 kg/cm @ 400 rpm/normal Starter cranking speed.
ii) Permissible Inter-cyl variation - (+/-) 1.0 kg/cm.
iii) Wear-down/service limit - 10.0 kg/cm.

Therefore, by implication, one can predict the remaining useful life of an engine by comparing its present CR with its values under (i) and (iii) above, vis a vis its ‘true’ Odo reading at the time of such a Test.

However, this will tell you about the state of its pistons/rings and valves only and not about its various other wear prone parts, such as journals/bearings etc. Only a ‘trained’ ear can tell the latter to some extent, by listening to its ‘noise spectrum’ at various loads/speeds.

A guide to all it does, and how it does it. The more we know about engine oils, the more wisely we can choose the best oil for our cars and MUV/SUVs.

Engine oils do more than you think. It’s easy to name the main function of engine oil: to lubricate every moving part of your engine with a protective film that reduces friction. But engine oil has at least four other duties, and failure to perform them all can seriously reduce the performance and life of your engine.

First, your engine oil cleans your engine. Gasoline and diesel engines can produce soot, ash, acids, and moisture that eventually form sludge, varnish, and resins. If they collect on critical engine parts, it means serious trouble. A quality engine oil keeps them suspended until filtered out or drained away when you change your oil.

Next, oil seals microscopic hills and valleys on piston rings and cylinder walls. Without proper sealing action, you’ll lose power and waste fuel.

Further, engine oil also protects your engine against rust and corrosion.

And finally, oil cools vital parts such as camshaft, rods, and pistons that the engine coolant in your radiator cannot reach. As much as 40% of the cooling job in your engine is performed by the oil in your crankcase.

Some facts about viscosity index

The Viscosity Index or ‘VI’ measures the change of an oil’s viscosity over a wide range of temperatures. The higher the VI of an oil, the less it will thicken when cold, and the less it will thin out when hot. A high VI oil will be more effective when lubricating your engine over a wide temperature range. Changes in viscosity and VI result in different viscosity grades, so you can pick the best grade for your vehicle.

Here’s a description of the five most common ‘SAE’ multi-grade oils:

0W-30: Premium winter grade oil. Provides year-round protection and fuel economy. Can be used where SAE 5W-30 is recommended.

5W-30: Premium multi-grade oil for easier cold-weather starts, maximum protection, excellent fuel economy and added engine life. The preferred grade for most cars built after 1989.

10W-30: The most commonly recommended multi-grade oil by OEMs in India. Delivers excellent all-round performance for the average driver.

10W-40: A premium multi-grade oil for hotter-than-normal running conditions, say where ambient temperatures exceed 40°C. It’s capable of providing extended engine life under such high temperature conditions.

20W-50: Thicker premium multi-grade oil for added protection against metal-to-metal contact; specially formulated to meet the needs of high performance Engines.

Making a change for the better

Today’s engines are efficient and sophisticated machines, often using multiple camshafts, turbo-chargers and other features. They also run faster and hotter, placing tremendous demands on engine oil performance.
That’s why it is essential to follow a strict oil-and-filter change schedule for your car. Changing the oil and filter remove harmful contaminants that may build up in your oil.

A fresh supply of engine oil with its specially selected additives will restore the protection your engine needs against corrosion, gum deposits, excessive wear, and other problems.

The oil and filter should be changed at the interval recommended in your owner’s manual. Every 5000 -10,000 km or 6-12 months is a common recommendation in India, especially for the BS-III Engines.

Speaking of performance additives

Most oils look, feel, and smell the same but their performance can be vastly different, thanks in part to their ‘in-built’ additives. Additives suspend dirt, inhibit foam, improve cold-weather flow, prevent corrosion, reduce friction, and add other qualities.

Many specialty additives or oil treatments are sold separately as brand names and promise longer life or extra performance for your engine. Remember that modern oils are recipes with measured portions of ingredients. Upsetting the recipe balance could lead to problems.

An oil formula may include a little anti-wear additive the same way a cake includes a pinch of salt to bring out flavour. If a little salt works, should you add more? Probably not, and the same goes for oil additives.

Believe in choosing the best quality oil you can afford and change it according to your Owners’ Manual is wiser in the long run.

Preamble
Prior to the ‘3-part series on F1 machines‘, we had a look at the philosophies behind F1 and Stock Cars’ tyres. So it occurred to me that a peep into the world of ‘Aircraft Tyres’ could be as interesting. I thus spoke at length with my ‘Tyre Guru’ – Mr. Sudershan S Gusain – and this is what transpired…

Today’s Aircrafts are a culmination of the state of art engineering know how of all disciplines – be it mechanical, structural, electrical or electronics. They more than ably fulfill mankind’s eternal desire to fly – literally around the world and in much less than 80-hours!

Present day commercial Jets have some unique features when it comes to their Tyres. For without their required ‘functionality’ AND ‘reliability’, they may perish at the drop of a hat – not to mention carrying hundreds of lives alongwith. Therefore, these two requirements take precedence over aesthetics.

Tread design of ACTs is ‘plain/rib’ type, since such patterns result in great ‘straight-line’ stability, smooth rolling, lower noise levels, less prone to irregular wear, along with very good ability in channeling out water on wet runways to eliminate loss of control while landing/take-off due to ‘aqua-planing’.

You may recall that this is similar to ‘wet’ F1 tyres. Besides, since Aircrafts do not zigzag or are called upon to traverse through soft ground, they don’t need to have Stock Car like tread patterns.

Tread rubbers of ACTs (as well as F1) tyres have to have great braking efficiency and high temperature withstand abilities. As a result, unlike Stock Cars, durability takes a back seat here. Besides, ACTs have also to face extreme operating conditions, such as:

1. They have to withstand very wide range of temperatures and that too within a short span of time. For example, at a cruising altitude of 10,000 meters, their ‘hold’ temperature can be low as (-) 45°C. Within half an hour or so upon ‘approach’ to landing, it changes from this to near ambient at ground level. And soon after ‘touch down’, their tread surface can rise to (+) 250°C or more! And nearly the same is true in reverse after a take off!
2. Load on an ACT is around 25-30 tons ‘per tyre’, as against a typical SUV @ ~800 kg per tyre and a typical truck @ ~ 4-6 tons per tyre.
3. Consequently, ‘inflation pressure’ in an ACT is very high. For commercial jets, it’s around 220 psi, as against 30~35 Psi of a stock car. For such reasons, ACTs (and F1’s) are filled with pure nitrogen out of necessity and this philosophy is trickling down to demanding stock car users as well.
4. The takeoff speed of an Aircraft depends on many parameters such as its ‘laden-weight’, the ambient air temp/density, wind direction/velocity etc. The take off speed of common jetliners these days is around 300 km/h and landing around 240 km/h.

Apart from the above/extreme operating conditions that ACTs have to withstand, their manufacturers have to keep their weight to minimum possible so as to minimize the aircraft’s fuel consumption. This is far from easy and one of the reasons why so few Companies around the world successfully produce ACTs to today’s demands. Because of such extreme requirements and limited tread depths, ACT tread wear’s are much faster and surprising as it may seem, it’s viable to ‘re-tread’ them today, as opposed to ‘Not Recommended’ for Stock Cars.

Accordingly, ACTs are sent for retreading after around 350 landings for Radial and 200 landings for Bias Ply tyres. On an average, a Radial ACT can be retreaded upto 3 times (350×3=1050 landings) and a Bias type upto 6 times (6×200=1200 landings). Quite like Stock Cars, Radial ACTs are preferred due to better rolling resistance, traction and the fact that they offer almost 150% higher number of landings between retreads.

However, unlike conventional retreading techniques, retreading an ACT is a highly evolved task. For example, after a retread, their balance and uniformity in all the domains has to be checked such that it conforms to the ‘original’ spec again. It’s for such reasons that leading ACT mfrs have plants dedicated just to retreads.

To conclude for present, it may interest you to know that the worlds most advanced commercial jetliner as on date, the ‘Airbus-A380’ has 20 nos tyres of size 1400×530R23/40PR in its rear under carriages and 2 nos 1270×455R22/32PR for the nose. Bridgestone Japan is the chosen vendor for these, producing them at their Plant in Kurume, Japan.
And, for a change, I’ll ask readers a question this time. Most of you may have read of ACTs bursting at take off, also. WHY? If you know the answer, e-mail it to expert@indiaautomobile.com ALONGWITH your full name and address. The correct ones received by Sunday the 16th March ’08 will be published in these columns next week i.e. Friday the 21st March ’08.

Preamble:
Having had a look earlier at the philosophy behind F1 vs Stock Cars Tyre designs, we had a glimpse last week behind reasons for constant need to maintain one’s tyre pressures ‘correctly’.

Contrary to what I said last week, I’ve just realised that I’ve already written about the importance of Wheel Balancing AND Alignment during the month of August ’07 itself. For those who tuned in later, please browse thro’ www.indiaautomobile.com/articles/archives/August.

So this week, let’s talk about other related issues, such as ‘Steering Wobbles’ and ‘Steering Rattles’…

Steering Wobbles

These are basically a) those occurring at cruising speeds and b) ones that occur at slower speeds, such as at take off and braking. While the former can largely be attributed to ‘dynamically-unbalanced’ wheels and to a lesser degree to ‘wheel-alignment’, the latter are caused by different reasons, such as – i) Unevenly worn front Tyres, ii) Out of true Wheel Rims, iii) Internally Damaged Radial Tyre Casing, iv) Worn-out Steering/Track Linkages/Suspension Bushes/Members, v) Damaged ‘Knuckle’ Joint, vi) Damaged Wheel End Axle Assy, vii) ‘Out of true’ Front Disc Brake Rotors, vii) Faulty/Worn out Caliper Assys OR sticky Hydraulic Piston/Rings thereof and viii) Defective Engine/GB Foundations, etc.

Steering Rattles

The real crunch here lies in identifying the source of such rattles as more often than not, with wear and tear setting in, a steering rattle gets sort of ‘progressive’ i.e. it can ‘shake’ other members of the ‘system’ into rattling which on their own may not! Such rattles can originate from one or more parts of the steering system as a whole.

Here’s how one can systematically analyse them, as those caused by – i) Premature wear of Tie-rod end/Rack ball joint: These can set in by ignoring the need to have all the five Wheels in good ‘dynamic balance’ all the time. This can be checked out by hoisting the vehicle on a 2-post lift and ‘yawing’ each front wheel horizontally - to ‘feel’ if there’s any slack around them; ii) Rack and/or Pinion wear: This again is a consequence of neglecting to keep one’s wheels in good balance all the times. These can be checked out by – a) parking the vehicle with wheels ‘st-ahead’ on a level ground and b) standing out side the driver side, gently rocking the steering wheel to the left/right. If there’s no slack per (i) above, then a slight steering wheel motion will reflect in front wheels’ motion also. If it doesn’t, it’s an indication of excessive slack between the rack and pinion. If it cannot be rectified by suitably tightening the rack ‘damper-bush’, the only remedy is to replace both with genuine parts at one go; iii) Rack ‘Bush’ Rattles: These are ‘softer-sounding’ in nature and can be pinned down by – a) parking the car on a level ground with engine off and b) ‘rocking’ the stg wheel gently. If one can hear soft thuds from the LHS end of the car even while sitting in the driver seat, the rack bush is the culprit and the only way to get rid of it is to replace with a genuine spare part; iv) St Column Rattles: These are relatively easier to identify as their origin is close by and one can hear them as ‘metallic’ in nature – may be extending upto the pinion. Since most Cars’ steering columns these days have ball bearings at its both ends, the main culprit of such noises is invariably the one or more of the ‘universal joints’ deployed between the steering column and the rack-pinion. This can be set right by getting the stg column suitably ‘tensioned’ at a skilled Garage.

With the foregoing trouble-shoot, most steering rattles can be overcome with lasting success. If not, one is left with no choice but to have one’s steering system suitably overhauled, including replacement of ‘all’ the wear prone parts at one go.

Cutting corners here is not advisable since a half-worn part which was otherwise ‘silent’ will now start rattling due to greater thrusts on it from the replaced/new parts!

Preamble:
Last week we had a glimpse into the philosophy behind the design of Tyres for F1 Racing Machines vs a Stock Car.

Considering the fact that your tyres are the only means of your communication with the road you drive on, they can either save you or kill you – depending upon what care you take in choosing AND maintaining them.

Here’s some more on how to look after your tyres…

Tyre Pressures – Do they Matter?

YES - they more than do! Here’re some basic facts:

1. The Tyres that come with your Car are the best suited for the purpose it’s intended for.
2. There’s an uncalled for mania in our Country to run down such OE Tyre specs, especially on the 80Bhp+ Cars.
3. When I say uncalled for, check out multitude of street cars in developed countries where none dare ‘up grading’ OE tyres coz then their Insurance Policies will become invalid and a crash out there, whether coz of tyres or not, can set one back by thousands in hard cash – assuming no life is lost!
4. Every ‘chosen’ Tyre has a ‘safe’ load bearing capacity - say 1/4th the ‘weight’ of a Car.
5. The Weight of a Car varies - from ‘Kerb’ to ‘fully loaded’ - for understandable reasons. This difference can be as much as 500 kgs!
6. The ‘ideal foot-print’ of a Tyre is a function of its inflation pressure when ‘cold’, AS WELL AS the load on it.
7. While in motion even a ‘correctly’ inflated tyre ‘warms-up’, coz of internal heat generation due it’s inevitable ‘flexing’ AND friction with the road surface. Consequently, the ‘cold’ pressures go up by as much as 15% on a high-speed cruise after some time.
8. All this is taken care of when carmakers stipulate ‘cold’ inflation pressures. They, however, take a medium route - by specifying cold pressures for ‘part load’, which is usually the case, and strike a compromise between fuel consumption - higher the cold pressures the better - and ride quality - lower the better.
9. Therefore, when going on a long trip, ‘fully loaded’ as is usually the case, inflation by +10% over the recommended cold pressures is highly recommended. The ‘effects’ of various degrees of ‘inflation’ are illustrated in the sketches below:
   
10. It’s obvious that one has to aim at correct pressures to give the best ‘foot-print’ between the tyre and the road.
11. Looking at above sketches, it may be noted that ‘under-inflated’ tyres will wear out faster from their outer edges and over-inflated ones from the middle. Only properly inflated ones can ensure even tread wear.

So how do we go about it!

Actually, it’s not that difficult, considering ‘Cold’ means when the tyres are at ‘Ambient’ temperature – ideally the first thing in the morning before one rolls off. Now that’s where crux of the problem lies. To overcome it, this is what you can do:

1. Ideally, you need a Tyre Pump and a reliable TP Gauge of your own - as most at the roadside are out of ‘synch’. If you find a foot pump bit of a bother, there are Battery operated ones available for ~ Rs: 500/-, which plug into the cigarette lighter socket.
2. Similarly, a good ‘dial type’ TPG can be had for ~ Rs: 100/- and a digital/self-calibrating type around Rs: 300/-. It’s strongly recommend that you buy your own tyre pressure gauge. Armed with this, you could also fill-up air at any pump, using your TPG.
3. What one can do and it works fine is that you get your Pressures corrected to, say (+) 10% per your Gauge’. Next morning before rolling off, check again with your TPG and let off excess pressure, if any.

Remember that Tyres under-inflated by as little as 4 psi can raise your fuel consumption by as much as 6% - besides seriously jeopardising their lives and thus your safety!

Next week we’ll discuss the importance of ‘Wheel Balancing’ and the need for their ‘alignment’.

Preamble:
Considering the fact that your tyres are the only means of your communication with the road you drive on, they can either save your life or kill you – depending upon what care you exercise in choosing AND maintaining them.

With a new car, the first part is taken care of beyond doubt, as other wise it won’t qualify as ‘street-legal’ for sale to public at large. Trouble comes when people mindlessly try to ‘upgrade’ them – leave alone neglecting them by way of properly maintaining their inflation pressures round the year, not to mention their ‘concentricity’, dynamic-balance and alignment.

So let’s first talk about the philosophy behind the design of our stock car tyres as explained to me by a Sr. Exec of a prominent MNC Tyre Co., when I picked his brains with the following questions posed by an enlightened visitor…

Questions
Regarding tyres, I’ve seen on TV and in Books that F1 tyres have 3-5 plain treads around or are completly plain, having full contact to the track. But in real life for our cars, we have lots of gaps, in the form of different tread designs. If these are worn out, i.e. when the tyre becomes bald we change it, which is in contrast with the idea on F1 machines where they run mostly on smooth tyres. Why can’t we use smooth tyres provided we run our cars only on metalled roads and not off-roads?

Answers
Our compliments to you on your observations and conclusions. Regrettably, what’s good for the Goose is seldom so for the Gander as well! Consider the following:

The ‘Road-Grip’ a tyre provides is directly related to the ‘Friction’ generated between road and the tyres. And ‘Friction’ is directly proportional to the ‘Coefficient of Friction’ and the ‘area’ in contact. Worn out tyres thus have more ‘area of contact’ on ‘flat’ roads whereas ‘CoF’ varies with road material (Tar, rubber mix or concrete), its finish (smooth, coarse) and of course tyre tread rubber ‘composition’ AND condition.

Tyres exposed to strong Sun/UV light for long or aged over time makes their rubber hard, leading to reduced CoF. CoF also reduces if it has just rained and again increases if it continues to rain for some time and water gets drained out from the road surface.

Let’s break your query into two now:

Q1. Why do the stock tyres have treads while F1’s don’t, and
Q2. Why is it not recommended to use worn out tyres i.e. that have no tread left.

A1.
F1 tyres for dry tracks do not have any tread for the reasons stated above i.e. max contact area and the fact that F1 tracks are clean - no mud, no dust etc. However, F1 tyres for wet surfaces do have grooves i.e. ‘Ribs’ which run circumferentially on tread, to channel out water so that there’s no water trapped between tread and road. If dry/flat tyres are used on wet tracks, there will be ‘hydro or aquaplaning’, which will result in skidding/loss of control. In reality, public roads are not exactly that flat and free of loose material. There is loose dust, sand, small stones and gravel all over the road.

So in stock tyres, we have to have tread patterns to assist channeling out of water, dirt and air (to reduce ‘rolling noise’) as in reality, we have to drive the same car/tyres in rainy season, on roads with dust particles, surface irregularities, and of course off the road some times. One more thing - to judge a worn out F1 tyre, expert inspection is needed, whereas in real life, any one can see if a treaded-tyre is worn out, tho’ most penny-wise pound-foolish types ignore it and keep on driving until steel wires come out or worse still, till the tube itself starts showing up!

A2.
A worn out tyre has better braking and traction on plain clean roads but it is not recommended to use worn out tyres on Stock as well as F1 vehicles because the roadside tyre-wall thickness reduces considerably. After such a degree of wear, chances of hydroplaning increase manifolds and even if there is no water on road or other obstacles, a tyre can burst due to sheer centrifugal force alone at high speeds.

Further, in Indian road conditions, due to their vulnerability towards cuts and bruises, worn out tyres have more chances of moisture seeping into steel belts, leading to their rusting and consequent loss of adhesion with rubber, causing belt separation and ultimately leading to tyre burst.

To sum-up, for F1 racing, all that matters is ‘grip’ and they’re no bothered about the costs of changing even up to 4-sets during one race that may not last even a few hundred kms. In real life, at average speeds that may not even be 1/10th of the F1, ‘cost per km’ to the owner is the overriding factor and a pax car tyre in India is expected to last at least 40-50 kkm - besides expectation of ‘reasonable’ grip under all possible surfaces that an average motorist is likely to drive on – hence a multitude of ‘tread designs’, each one claiming to be superior than other!

Preamble
A couple of months ago, I wrote about the Electrical Systems of present day cars and how they are a far cry today from the Amby’s and Fiat’s of yore. While the advent of ‘Alternators’ solved a lot of problems, but as was to be expected, people got confronted with new ones they hadn’t faced before.

Well, as usual some intelligent fellow asked me some more Q’s on the last week’s writing. This is how it went with him this time…

Question:
As per what this Indica gentleman had to say, he observed that the engine temp. gauge gradually increases (to the red zone) and then decreases. If Voltage Regulator is defective, shouldn’t it remain ‘high’ all the time? VG/Mumbai.

Answer
Having personally experienced Voltage Regulator malfunctions on M800s more than once, the Alternator over-voltages are ‘transient’ in nature and occur almost ‘instantaneously’ for all practical purposes. These manifest as brightening up of head lamps, if driving at night, and shrilling up of the horn - which are on day and night in our scenario, accompanied by ‘consequential and pronounced’ drag on a small engine like the M800’s. The latter is caused by the Alternator imposing greater load on the engine, as it’s called upon to push more Amps due to the over-voltage condition, through whatever loads it’s connected to at that time.

Such over voltages last for a few seconds and then settle down, only to happen again unpredictably - due to the malfunction of the IC-controlled/in-built all solid state Voltage Regulators.

However, since the Temp Gauge and the Fuel Gauge now a days are of ‘viscous-damped’ type, the former being ’stay-put’ in addition, they don’t respond to the over voltage condition ‘instantaneously’ but will register a ‘well-damped rise’ to their max position – something like the fuel gauge after you’ve filled up to ‘F’ from ‘E’ and drive off. .

Likewise when the over voltage condition disappears after a while - entirely at the sweet will of the VR. In petrol Mpfi’s, the ECU may shut off too, due to its in-built over voltage protection. In that case, it’ll switch over to ‘limp-home’ mode as programmed, with the engine/RCU light coming up on the Dashboard. However, I’ve yet to experience such a condition either on my 7 yr+/80Kkm old Santro or ~ 4 yr/12K km old Baleno.