Haryana BSEH Senior Secondary NSQF Automotive cheat sheet

Fire classes: A = solid combustibles (water/foam), B = flammable liquids (foam, CO2, dry powder), C = flammable gases (dry powder), D = combustible metals (dry powder only), E = electrical (CO2, dry powder; never water).

Compressed air for cleaning must be limited to 30 psi (approx. 2 bar) with a chip guard; higher pressure can force debris through skin.

Jack stands are rated in pairs; a 2-tonne pair supports 2 tonnes total, and the vehicle must be chocked on the opposite axle before any work under it.

Battery charging releases hydrogen; keep flames and sparks at least 1 m away and ventilate the area because hydrogen ignites between 4% and 75% in air.

CO is odourless and binds haemoglobin about 200-250 times more strongly than oxygen; never run an engine in a closed bay - use a hose to the outside.

PPE decision rule: eye protection for grinding, cutting, drilling, battery and brake work; gloves for solvents, hot metal and sharp edges; never wear gloves or loose sleeves near a rotating shaft or bench grinder.

Refrigerant R-134a must never be vented; recovery is required, and liquid refrigerant contacting skin causes frostbite at about -26 C.

Brake linings and clutch facings may contain asbestos in older vehicles: use wet methods or vacuum extraction, never dry compressed air.

Torque = force x perpendicular distance (T = F x d); a 40 N force on a 0.5 m wrench gives 20 N·m.

Torque wrench accuracy is typically +/-4% of setting over the upper 20-100% of scale; never use a torque wrench to loosen fasteners or drop it.

Micrometer reading = main scale + thimble: 0.5 mm main divisions, 50 thimble divisions on a 0.5 mm lead give 0.01 mm per division.

Vernier caliper least count = main scale division / number of vernier divisions; typical metric caliper: 1 mm / 20 = 0.05 mm, or 1 mm / 50 = 0.02 mm.

Bore gauge or inside micrometer measures cylinder bore; measure at three heights and two planes (thrust and axial) to detect taper and out-of-round.

Feeler gauge blades are marked in mm or inches; combine blades additively, and a 0.05 mm difference between go and no-go indicates correct clearance.

Tap drill size for metric coarse threads: drill diameter = major diameter - pitch (e.g., M8 x 1.25 uses 6.75 mm, usually 6.8 mm).

Hydraulic press capacity rule: force = pressure x piston area; a 10-tonne press with a 50 mm ram needs about 500 bar at full load.

Four-stroke cycle order: intake, compression, power, expansion/exhaust; crankshaft makes two revolutions per cycle, camshaft one (2:1 ratio).

Compression ratio = (swept volume + clearance volume) / clearance volume; a 500 cc cylinder with 50 cc clearance gives 11:1.

Engine displacement = cylinder area x stroke x number of cylinders; a 4-cylinder engine with 80 mm bore and 90 mm stroke displaces about 1,810 cc.

Valve clearance is set with the engine cold unless specified; typical clearance 0.15-0.30 mm intake and 0.25-0.35 mm exhaust, checked at TDC on compression for that cylinder.

Cylinder taper limit is usually 0.05-0.10 mm and out-of-round 0.02-0.05 mm; beyond limits requires reboring or replacement.

Piston ring end gap rule of thumb: 0.003-0.004 mm per mm of bore for top ring; a 90 mm bore gives about 0.27-0.36 mm.

Head bolt tightening is usually torque-to-yield or a torque-plus-angle sequence, always from centre outward in a spiral to avoid head distortion.

Oil pressure warning at idle below about 0.5-1.0 bar indicates worn bearings, a faulty relief valve, or a blocked pickup; normal hot idle is 1-2 bar.

Manual gearbox ratio = driven gear teeth / driving gear teeth; overall ratio = gearbox ratio x final drive ratio.

Clutch free play is typically 10-25 mm at the pedal; too little causes slip, too much causes incomplete disengagement and gear clash.

Synchroniser rings must have a clearance of about 0.5-1.5 mm to the gear cone; less than 0.5 mm indicates worn rings and gear crunch.

Differential ratio = ring gear teeth / pinion teeth; hypoid pinion depth and backlash are set with shims, typical backlash 0.10-0.20 mm.

In an open differential, both wheels receive equal torque but can rotate at different speeds; a locked or welded diff forces equal speed and causes tyre scrub in turns.

CV joint boot split causes grease loss and grit entry; clicking on full lock indicates worn outer CV joint, vibration under acceleration indicates inner joint.

Automatic transmission fluid level is checked with the engine running in Park or Neutral at operating temperature (about 70-80 C) per the dipstick marking.

Propshaft universal joint phasing: yokes must be aligned in the same plane to avoid vibration; a 180-degree misalignment produces a twice-per-revolution vibration.

Hydraulic pressure = force / area; a 200 N pedal force on a 20 mm master cylinder gives about 0.64 N/mm², multiplied by caliper piston area for clamping force.

Brake fluid DOT 3 and DOT 4 are glycol-based and hygroscopic; DOT 5 is silicone and must not be mixed with glycol fluids.

Brake fluid boiling point drops with absorbed water: DOT 4 dry about 230 C, wet about 155 C; typical replacement interval is 2 years.

Disc runout limit is usually 0.05 mm or less; excessive runout causes pedal pulsation and requires machining or replacement.

Minimum brake pad friction material thickness is typically 2-3 mm; replace pads before the backing plate contacts the disc.

Steering wheel free play should not exceed about 25 mm (1 inch) measured at the rim; excess indicates worn tie rods, steering box, or column joints.

Wheel alignment: camber is vertical tilt, caster is steering axis tilt fore/aft, toe is the difference in front/rear distance between wheels; total toe is usually within +/-0.2 degrees.

Tyre rotation and balance: imbalance shows as vibration at a road-speed-related frequency; static imbalance causes hop, dynamic imbalance causes shimmy.

Ohm's law: V = I x R; power P = V x I = I²R. A 12 V circuit drawing 5 A has 2.4 ohm resistance and dissipates 60 W.

Series circuit: total resistance adds, current is common, voltage divides. Parallel circuit: voltage is common, current divides, total resistance is less than the smallest branch.

Battery capacity in Ah = current x time; a 60 Ah battery can supply 3 A for about 20 hours at the 20-hour rate.

Alternator output is regulated to about 13.8-14.4 V at 20 C; below 13.2 V suggests a faulty regulator, diode, or belt slip.

Starter current draw on a small petrol engine is typically 150-250 A; a voltage drop test should show less than 0.5 V on the positive and ground paths under load.

A fully charged lead-acid cell reads about 2.1 V open circuit; a 12 V battery at 12.6 V is about 100% state of charge, 12.0 V about 25%.

LED and ECU circuits are polarity sensitive; never test with a high-current test lamp - use a high-impedance multimeter (10 MΩ or more).

Fuse rating must match the circuit; a 10 A fuse protects wiring rated for about 10 A continuous; never upsize a fuse to stop it blowing.

Petrol stoichiometric air-fuel ratio is about 14.7:1 by mass; diesel is about 14.5:1; rich mixtures (below 14.7) raise CO and HC.

Lambda = actual AFR / stoichiometric AFR; lambda 1.00 is ideal, and the oxygen sensor switches around 0.45 V at stoichiometry.

Three-way catalytic converter reduces CO, HC and NOx only within a narrow lambda window near 1.00; lead and sulphur poison the catalyst.

EGR reduces NOx by lowering combustion temperature; excessive EGR causes rough idle and misfire, insufficient EGR raises NOx.

PCV valve recirculates crankcase blow-by gases into the intake; a blocked PCV raises crankcase pressure and causes oil seal leaks.

Diesel smoke: black = over-fuelling or restricted air, blue = lube oil burning, white = unburnt fuel or coolant ingress.

CNG and LPG have higher octane than petrol (CNG about 120 RON) but lower volumetric energy density, reducing power by roughly 10-15%.

Biodiesel blends above B5 may degrade older rubber seals; ethanol E10 is hygroscopic and requires compatible fuel-system materials.

Paint system layers: pretreatment/phosphate, primer, base coat, clear coat; total dry film thickness typically 80-120 micrometres.

Surface preparation grades: 80-120 grit for stripping, 180-240 grit for primer sanding, 400-600 grit before base coat, 1000-1500 grit for blending.

Orange peel is caused by too-fast thinner, low spray pressure, or too-thick coats; runs are caused by too much material per pass or a too-close gun.

Spray gun distance is typically 15-20 cm with 50% overlap; a 1.3-1.4 mm fluid tip suits base coat, 1.4-1.8 mm suits primer or high-build.

Colour match requires checking a spray-out card under daylight (D65) and comparing metallic orientation; flop angle changes the face colour.

Body filler must be applied over bare metal or properly sanded primer, never over paint or rust; maximum thickness is usually 3-5 mm per application.

Panel gap and flushness targets are typically 4-6 mm gap and +/-1 mm flush; check with a gap gauge before final paint.

MIG welding thin body steel (0.7-1.0 mm) uses 0.6-0.8 mm wire, 40-90 A, and short stitch welds to limit heat distortion.

Diagnostic sequence: verify the complaint, gather symptoms, check for DTCs, confirm with a functional test, then repair and re-test; never replace parts on a guess.

OBD-II DTC format: P = powertrain, B = body, C = chassis, U = network; the second character 0 = generic, 1 = manufacturer-specific.

Fuel trim: positive long-term trim (above +10%) indicates a lean condition (vacuum leak, weak pump); negative trim indicates rich.

Vacuum gauge readings: steady 17-22 inHg at idle is normal; a fluctuating needle suggests a vacuum leak or valve problem; a low steady reading suggests a restriction.

Compression test: cranking with throttle open and all plugs removed; a variation of more than 10% between cylinders indicates a problem.

Cylinder leakage test: air at about 100 psi; leakage past the intake = intake valve, past the exhaust = exhaust valve, into the crankcase = rings.

Brake inspection includes pad thickness, disc thickness and runout, hose condition, fluid level and moisture, and a road test for pull or pulsation.

Tyre tread minimum in India is 1.6 mm; check wear indicators and uneven wear patterns (centre = over-inflation, edges = under-inflation, one side = alignment).

Break-even quantity = fixed cost / (selling price per unit - variable cost per unit); a workshop with 50,000 fixed cost and 500 contribution per job needs 100 jobs.

Gross profit = revenue - cost of goods sold; net profit = gross profit - operating expenses; margin % = profit / revenue x 100.

GST registration threshold for most Indian states is 40 lakh turnover for goods and 20 lakh for services; composition scheme limits differ.

Quotation must state scope, parts, labour hours, taxes, warranty and payment terms; a verbal estimate is not a contract.

Job card fields: customer details, vehicle registration, odometer, complaint, work authorised, parts used, technician signature, delivery date.

Customer complaint handling: acknowledge, listen without interruption, confirm the facts, offer options, agree a resolution and follow up.

MSME Udyam registration gives access to collateral-free loans under CGTMSE and priority-sector lending; keep records for at least 8 years.

Workplace ethics: never fit used parts as new, disclose additional faults before repair, and return replaced parts to the customer on request.

Torque specification lookup: use the manufacturer's value for the fastener grade and lubrication state; dry and lubricated torques differ by about 20-30%.

Fastener grade marking: 8.8 means tensile strength 800 MPa and yield 80% of tensile; 10.9 means 1000 MPa and 90% yield.

Measurement uncertainty: use the instrument with resolution at least 10 times finer than the tolerance being checked (e.g., 0.01 mm for a 0.1 mm tolerance).

Locking methods: thread-locking compound for vibration, split pins and lock wire for critical joints, and never reuse torque-to-yield bolts.

Project report structure: title, objective, literature/background, method, observations with tables, calculations, results, conclusion, references.

Record observations in a table with units and instrument used; repeat each measurement three times and report the mean and range.

Run-in after overhaul: change oil and filter after the first 500-1,000 km, re-torque head bolts if specified, and check for leaks at operating temperature.

5S in the workshop: sort, set in order, shine, standardise, sustain; tools returned to marked locations reduce lost time and injury.