Before proceeding to overhauling of engine it is desirable to have a preliminary inspection of the engine to ascertain whether an overhaul is necessary and to what extent. Check vehicle log book and check total kilometre covered by engine after last major overhaul and since inducted in service. Check for any major component change or repair carried out. Check if any defect was repetitive in nature and what repair was carried out. Check general condition of chassis and body of vehicle. At present in Air Force minimum life of diesel engine is 75,000 KM and life of TATA Sumo vehicle is 1,20,000 KM. By studying all above facts decision should be taken for carrying out major overhaul and to make the vehicle road worthy.
Inspection of Engine Before Overhauling
Most common reasons for which engine is overhauled are.
(a) Loss of power. Loss of engine power may be due to.
(i) Defective Fuel System. Check condition of fuel filter elements, fuel injection timing, injection nozzles and fuel injection pump for proper functioning.
(ii) Clogged Air Cleaner / Exhaust Silencer. Loss of power with unusual black smoke from engine exhaust indicates lack of air or low air charging pressure to engine cylinders. Clean the air cleaner. Check all joints for air leakage. If power loss with black smoke is still felt, check exhaust silencer for choking. Check and replace silencer if necessary.
(iii) Clutch Slippage. Clutch slipping can be confirmed by any of the following two methods.
(aa) Drive vehicle in 1st and 2nd gear at maximum speed corresponding to that gear. With accelerator pedal fully pressed, apply brake gradually with left foot. If the engine stalls, it means that clutch does not slip.
(ab) Drive loaded vehicle in 3rd gear on level ground and let the speed drop down to approximately 15 kmph. Now press accelerator pedal fully. With slipping clutch, the vehicle speed will not pick up and also clutch burning smell will be noticed. If this does not occur and vehicle picks up speed, it indicates that clutch does not slip.
(iv) Brake Binding. During driving apply brakes number of times and then shift gear to neutral position. Check brake drums for over-heating and if necessary jack up axles and check wheels for free rotation.
(v) Loss of Engine Compression. If loss of power is not on account of defective fuel system, lack of air, choked exhaust silencer, clutch slipping and brake binding, check engine compression.
Low compression pressure may be due to leakage past valves / piston rings / blown cylinder head gasket. To ascertain the point of leakage, spray small quantity of clean engine oil in to cylinder showing low pressure and re-check compression pressure. If it improves, wear in piston rings / cylinder bore is indicated. If it does not, leakage past the valves is indicated. If compression pressure of adjacent cylinder is also on lower side, it may be due to blown cylinder head gasket.
(b) Excessive Engine Oil Consumption. Overhauling of engine may also be necessary due to high engine oil consumption. Since the oil consumption depends upon the various factors i.e. method of driving, pay load and speed, road conditions etc, therefore, before dismantling the engine, the oil consumption value need to be ascertained by conducting vehicle trials under normal conditions as follows:
(i) Check the external oil leakages and rectify them before commencing trials.
(ii) Take a clean vessel of 10 litres capacity and weigh it.
(iii) Place vehicle on level ground. This location will be the reference point for every measurement of oil.
(iv) Warm up engine. Cooling system temperature should be 75º – 80º C. Switch off the engine.
(v) Immediately unscrew drain plug of oil sump and let warm oil drain for 20 minutes into previously prepared clean vessel.
(vi) Check the engine for 10 seconds without accelerating engine. Allow oil to drain for 5 more minutes and repeat it 3 – 4 times.
(vii) Refit drain plug and tighten it.
(viii) Weigh the vessel with drained oil. Add or remove engine oil to obtain weight corresponding to maximum oil capacity. Weight of oil ‘X’ (gms) = Weight measured – Weight of vessel.
(ix) Pour weighed oil carefully into engine avoiding any spilling.
(x) Load the vehicle approximately to rated GVW. Drive vehicle for at least 200 km under normal operating conditions.
(xi) At the end of test drive, park the vehicle at reference point and drain the oil in same vessel as per draining procedure mentioned.
(xii) Again weigh the vessel with drained.
* Specific gravity of oil
These trials to be repeated to ascertain the oil consumption value. If oil consumption value is more than 0.15 ltr/100 km, then engine needs to be overhauled.
(c) Excessive Low Engine Oil Pressure. Check the following:
(i) External leakages.
(ii) Oil level in sump upto maximum mark on dipstick.
(iii) Oil pressure indicator for proper functioning.
(iv) Functioning of pressure relief valve on oil pump.
(v) Oil pump performance.
If oil pressure is found to be less than 2.8 bar at maximum speed and 1.2 bar at idling speed, this may be due to improper functioning of oil pump or defect in oil pump relief valve.
If low oil pressure is not on account of above factors, wear of journals / bearings is indicated for which overhaul of engine may be considered.
(d) Mechanical Failures Metallic knocking sound from an engine may be due to faulty injection, excessive clearance in main and big end bearings, small end bush, tappets, piston slap, seizing of piston rings, scored cylinder bore or breakage of any moving parts. Noise due to defective fuel injection equipment is generally termed as ‘DIESEL KNOCK’ and can be eliminated by attending to fuel injection equipment. By cutting off high pressure line to individual injectors with engine running will pin point the cylinder with Diesel Knock. Overhauling of fuel system will set right Diesel Knock.
Removal of Radiator
(a) Before proceeding for removal of radiator, ensure that cooling system is at room temperature.
(b) Remove the radiator cap.
(c) Drain coolant from the cooling system through radiator drain cock.
(d) Fit back the radiator cap and drain cock.
(e) Remove the radiator hoses connected to the water pump and upper cooling line.
(f) Disconnect pipe from radiator to auxiliary tank.
(g) Remove fan shroud bottom and top halves.
(h) Dismount the mountings bolt and remove the radiator.
Removal of Engine
(a) Remove bonnet.
(b) Disconnect electrical cable connections from:-
(ii) Starter motor.
(iv) Fuel injection pump solenoid switch.
(v) Oil pressure switch.
(vi) Glow plugs.
(vii) Water temperature transducer.
(viii) Reversing switch.
(c) Disconnect cables from:-
(ii) Speedometer drive
(d) Disconnect pipe lines from.
(i) Fuel filter to fuel injection pump.
(ii) Fuel injection pump to fuel tank
(iii) Vacuum pump to vacuum booster
(iv) Power steering pump (if fitted)
(e) Disconnect exhaust pipe from exhaust manifold.
(f) Drain engine lubricating oil from oil sump.
(g) Drain coolant from cooling system.
(h) Disconnect hoses from and to radiator.
(j) Disconnect pipe from radiator to auxiliary tank.
(k) Remove hose from air filter to air distributor.
(l) Disconnect propeller shaft front end.
(m) Remove the following sub assemblies:
(i) Air filter, if necessary.
(ii) Starter motor.
(iii) Radiator with fan shroud.
(iv) Clutch slave cylinder.
(v) Gear shift lever.
(vi) Gear box with clutch housing.
(n) Fix chain to front and rear engine lifting hooks and hold chain in position with crane.
(o) Unscrew and remove engine mounting bolts.
(p) Lift engine from vehicle with the help of crane.
(q) Mount engine on work stand.
Dismantling of the Engine
Remove all left over sub components from engine and dismantle the engine in following sequence.
(a) Cylinder Head Removal
(i) Remove high pressure pipelines and FIP with bracket.
(ii) Remove exhaust manifold.
(iii) Remove cylinder head cover.
(iv) Remove front gear cover and remove camshaft gear.
(v) Remove belt tensioner.
(vi) Loosen the cylinder head bolts and remove in sequence from centre to outward.
(vii) Remove the cylinder head and place it on work bench.
(b) Piston Removal
(i) Keep the engine up side down on the workbench.
(ii) Uniformly and evenly unscrew oil sump mounting screws and remove oil sump.
(iii) Remove crank case front cover with crankshaft oil seal.
(iv) Unscrew oil pump mounting bolts and remove oil pump with chain.
(v) Remove carbon deposit from top of cylinder bore with broken piston ring.
(vi) Turn the crankshaft and bring pair of pistons at BDC.
(vii) Unscrew connecting rod bearing cap bolts and remove it with bearing shells.
(viii) Push the piston assemblies out of cylinder bore using wooden handle of mallet.
(ix) Remove other two pistons in same way.
(x) Remove piston rings from piston and circlip from piston pin. Remove piston pin and detach piston from connecting rod.
(c) Crankshaft Removal As cylinder head and pistons are removed, for removing crankshaft proceed as following.
(i) Unstake lock plates and remove flywheel-mounting bolts. Remove the flywheel.
(ii) Remove main bearing caps with bearing shells
(iii) Mark shell bearing rear side with paint in case bearings are to be re-used.
(iv) Remove the crankshaft from cylinder block.
(v) Clean the crankshaft and inspect for wear, damage, breakage and overheating.
(d) Liner Removal. For removing liner from cylinder block proceed as follows.
(i) Keep the cylinder block up side down on hydraulic press so that bore from which liner is to be removed lies clear in table slot.
(ii) Ensure that cylinder block is resting squarely on the machine bed.
(iii) Keep special tool and press out the liner with the help of hydraulic press.
(iv) Remove other three liners in same way.
(v) Remove oil cooler from right side of cylinder block.
(vi) Clean cylinder block and inspect for any defect or damage.
Dismantling of Cylinder Head
For dismantling cylinder head proceed as following.
(a) Remove glow plugs and injectors.
(b) Remove camshaft-bearing caps. Remove camshaft with oil seal.
(c) Remove tappets and shims. Keep them in sequence at a safe place.
(d) With the help of spring compressor compress spring and remove valve half locks.
(e) Remove valve springs and valves.
(f) Remove valve guides with help of special drift. If required remove valve seats also.
(g) Use copper punch through injector hole and press out pre – combustion chamber.
(h) Clean the cylinder head properly and inspect for any defect or damage.
Servicing of Sub Components
For carrying major overhaul each component should be serviced and assembled. In case some parts are worn out excessively should be replaced by new one. Assemble the main components in following manner.
(a) Servicing of Cylinder Head.
(i) After cleaning the cylinder head properly place it on suitable workbench.
(ii) Use straight edge and filler gauge, check cylinder head mating surface with cylinder head
(iii) Maximum permissible unevenness lengthwise is 0.030mm and crosswise 0.015mm. If unevenness is more than these limits, cylinder head needs replacement.
(iv) Check valve guides and valve seats, for correctness and replace if required.
(v) Carry out valve grinding and change valves in case they are burnt, bent, scored or seats pitted.
(vi) Install pre-combustion chamber and measure the collar height.
(b) Camshaft Inspection. (Check camshaft for the followings).
(i) Carry out visual inspection of camshaft for over- heating of journals, which are indicated by brown colour.
(ii) Deep scoring marks on journals and cam lobes.
(iii) Inspect camshaft for scoring and over heating of journals, check cracks with magnetic detector.
(iv) Check hardness of camshaft journals and cam lobes. It should be 48.54 HRC.
(v) Check camshaft run out at 2nd and 4th journals by supporting on V blocks.
(vi) Check camshaft journal dimensions in case these are beyond permitted limits change the camshaft.
(c) Assembly of Cylinder Head. When all cylinder head parts are inspected and serviced, start assembling the cylinder head as follows.
(i) Fit back the valves with their springs and locking half’s.
(ii) For fitting tappets, install thinnest size of shims and apply light coat of molly paste grease over shims.
(iii) Smear tappet out side diameter with engine oil. Install the tappets in their respective positions.
(iv) Smear camshaft journals and cam lobes with molly paste grease and install camshaft with arrow marks pointing towards engine front.
(v) Install camshaft bearing with caps in their respective position with arrow marks pointing towards engine front.
(vi) Tighten the camshaft bearing cap nuts with new washers to torque 1.5mkg.
(vii) Check camshaft axial play it should be within specified limits.
(viii) Check camshaft for rotation the friction force should be 1.8 to 2.2 mkg.
(ix) Install woodruff key and camshaft gear with spacer. Tighten the camshaft gear mounting to 4.5 mkg torque.
(d) Tappet Adjustment In TATA Sumo vehicle tappet clearance can be adjusted when cylinder head is removed or installed in vehicle. Here we will adjust tappet clearance in cylinder head removed condition.
(i) Turn the camshaft and note down the valve clearance and adjust as follows.
(ii) Note respective valve clearances in sequence. It can be measured by inserting the feeler gauge between camshaft eccentric low heel and valve top portion.
(iii) If valve clearance is beyond the correct sizes. Calculate correct size of shims from range of 2.400 to 3.550 mm in steps of 0.050 mm to specified valve clearance.
(iv) Apply molly paste grease on both sides of determined shims and install them on there respective positions.
(v) Recheck the valve clearance and if found incorrect, readjust the valve clearance in same manner.
(e) Servicing of Pistons In case cylinder bore taperness and ovality is within specified limits, same pistons can be re-used. Service the pistons in following manner.
(i) Clean the pistons and remove the carbon deposit with broken piston ring and wooden chisel.
(ii) Examine pistons for cracks, scoring, ring groove wear, piston pin bore wear and spring clip groove wear.
(iii) In case one piston is worn out complete piston set should be changed.
(iv) Piston size is stamped on its crown.
(v) Examine piston rings for scoring, lateral clearance in piston ring groove and butt clearance in bore.
(vi) Always change piston rings in set only.
(f) Connecting Rod Inspection Inspect and service connecting rod in the following manner.
(i) Check connecting rod for excessive wear, bend, twist or damage.
(ii) Check connecting rod small end and big end parent bore.
(iii) Install connecting rod bearing caps with bearing shells and tighten to torque 5.0 mkg.
(iv) Loosen one nut of big end and measure pre- tension of connecting rod.
(v) Connecting rod bearings shells are precision finished and should not be bored or scraped.
(g) Inspecting crankshaft
(i) Clean the crankshaft and carry out visual inspection.
(ii) Check over-heating, scoring or any damage. Check cracks with magnetic crack detector.
(iii) Check hardness of the crankshaft.
(iv) Check crankshaft for bend, bow and twist by supporting it on V blocks at 1st and 5th main bearing journals.
(v) Check main bearing and crank pin journal dimensions. If necessary grind it to next under size.
(vi) Ensure that during grinding the width of the journals should not increase.
(vii) Re-chamfers the oil holes on journals to avoid scoring of new bearing shells.
(viii) Finish Journals by lapping with 32 grade lapping cloth of suitable width.
(ix) After regrinding check main bearing and crank pin journal diameter and run out.
(x) Clean crankshaft in kerosene use wire brush for cleaning oil holes.
(xi) Check the crankshaft dimensions are within these limits. If wear out is more, change the crankshaft.
(h) Servicing of Flywheel.
(i) Check wear out, scoring and colour of flywheel facing. The maximum permissible radial or lateral run out of the flywheel should not exceed 0.10 mm.
(ii) Check condition of flywheel ring, if teeth are damaged remove old ring by heating it with the help of blow lamp.
(iii) When flywheel cools down heat new flywheel ring to 200º C and install it facing chamfered portion towards front.
(iv) Check flywheel-mounting holes for elongation.
(v) Re-machine friction surface up to 1.00 mm, If scoring is beyond the limit of skimming change the flywheel.
(i) Cylinder Block Checking.
(i) Check cylinder block for cracks by pressure testing method.
(ii) Check crankcase, mating surface with cylinder head for unevenness. If required grind the surface just to clear unevenness.
(iii) Clean thoroughly main bearing caps by mating serial numbers and tighten the bolts to 7.0 mkg torque. Check main bearing parent bore dimensions.
(iv) Fit new bearing shells and tighten the bearings to specified 7.0 mkg torque and measure the parent bore of bearing.
(j) Cylinder Bores. Clean cylinder bores thoroughly and check cylinder bores dimensions for taperness and ovality. If taperness and ovality is more than specified limits or bore is worn out excessively re-bore it to next over size. Selection of bore size to which bore should be machined should be done as following:-
(i) Bore diameter of worn out cylinder.
(ii) Size of next over size piston available.
(iii) Recommended clearance between piston and bore.
(iv) Required bore diameter.
(v) Machine bores leaving 0.050 to 0.070 mm for honing.
(vi) In case it is observed that liner cannot be serviced by reboring, new liner should be replaced with hydraulic press.
(k) Installation of Liners In case liners are removed install the liners in following manner.
(i) Thoroughly clean bores of cylinder and liner.
(ii) Place cylinder block in hydraulic press ensuring oil sump mating surface is resting evenly and squarely on horizontal bed.
(iii) Do not smear cylinder bore of block or liner outside with oil.
(iv) Place liners with proper orientation (matching minimum/maximum ovality axis) in the cylinder bores and make it right angles to cylinder block top surface in longitudinal and crosswise direction.
(v) Press liner using special drift and a wooden spacer between press-ram and drift. Pressing force should be 4 to 6 ton.
(vi) Press other liners in same way.
Assembling of Engine
In last chapter we have learned dismantling of engine and servicing of sub components. When all sub components are serviced assembling of engine is done in following sequence.
(vii) Apply a thin coat of maxi fix adhesive in groove and allow drying for 10 minutes.
(viii)Assemble both side seals on 5th main bearing avoiding air bubbles and press firmly. Cut off the extra seal keeping 2 mm projection above cap height.
(ix)Install 5th main bearing by applying ‘Annabond’ 611 between mating surfaces of 5th main bearing and cylinder block.
(x)Tighten main bearing cap bolts to a torque of 7 mkg as per sequence.
(xi) Check the end float and install rear oil seal.
(xii) Install fly wheel and check the free rotation
(ii) Insert piston pin and fit circlip.
(iii)Turn crankshaft and bring crank pin journal to top most position on which piston is to be installed.
(iv)Position the piston ring gap and insert piston with connecting rod in cylinder bore with arrow on the piston facing to front.
(v)Install piston with piston ring compressor. Push over piston gradually inside the cylinder bore using wooden handle of mallet till connecting rod big end locates on crank pin journal.
(vi)Slowly rotate crankshaft and push piston till it reaches at BDC.
(viii) Tighten the bearing cap bolts to 5 mkg torque.
(ix)Install other piston in same manner and check free rotation of crankshaft.
(ii) Fit idler roller and fan mounting bearing block, tension spring, plunger and tension rollers.
(iii) Install woodruff keys on crankshaft front end.
(iv) Slightly tap timing gear and push it on crankshaft.
(v) Install crank shaft pulley in position
(vi) Screw in the crankshaft-mounting bolts with spacer and tighten it to 4 mkg torque.
(ii) Ensure that cylinder head locating hollow dowel is in position in crankcase.
(iii) Ensure that timing pin is installed in position.
(iv) Install cylinder head and tighten cylinder head mountings to 5 mkg torque from centre to outwards then retighten to 7 mkg torque in same sequence.
(vi) Fit cylinder head cover.
(ii) Fit alternator top and bottom bracket and alternator.
(iii) Fit water pump with new gasket.
(iv) Fit oil cooler with new gasket.
(v) Fit new oil filter.
(vi) Fit oil pipes for vacuum pump.
(vii) Install clutch plate and pressure plate.
(viii) Fit inlet and exhaust manifold.
(ix) Fit thermostat, upper and lower cooling line.
Installation of Engine on Vehicle and Engine Testing
(a) Check engine mounting pads for wear. Replace them if necessary.
(b) Install the engine in reverse sequence of removal.
(c) Tighten engine mounting bolts to specified torque.
(d) Connect all pipes, hoses and electrical connections.
(e) Fill coolant in the cooling system through radiator.
(f) Crank the engine momentarily. Let oil and coolant circulate through the system.
(g) Confirm whether oil pressure gauge is indicating the correct reading.
(h) Check for any leakage, rectify if necessary.
(j) Top up coolant upto FULL mark in auxiliary tank, if necessary.
(k) Start the engine and run for 10 minutes at 3000 rpm observe for any abnormal noise coming from running engine.
(l) Allow the engine to cool down for 2 hour 30 min.
(m) Remove radiator cap to release any excess pressure.
(n) Loosen one cylinder head bolt at a time by quarter turn and retorque to 7 mkg. This operation is to be carried out from centre to outward sequence only.