Sub: - Magnet valve maintenance.

Recently Loco No. 16167  failed on 8/7 due to reverser magnet valve defective.

          Sheds are advised to incorporate following maintenance practices in magnet valve checking & OVH to ensure reliability.

·          Measure operation time of power contactor & reverser. Note operation timing variation amongst different power contactors. Magnet valves linked to sluggish operation should be replaced. Uniform lower application timing in all contactors is desirable. Trend of application time should be monitored as predictive maintenance tool.

·         Look for sign of oil, moisture & dirt in magnet valve & attend in every schedule.

·         Measure air inlet pressure of magnet valves. If air pressure is less than 5kg/cm2, look for leakage in pipe lines and arrest the same.

·         Use of Bhel type modified magnet valve & checking condition of thread & adapter of pneumatic pipe.

·         Lapping of magnet valve during OVH. Lapping machine should be procured/fabricated in every test room.

·         Identical operation time of valve and power contactor in MEP locomotives to avoid logging of fault .

·         Ensure proper locking of fasteners and provide a locking plate to avoid loosening on run. It must be ensured during pre-commissioning of locomotives after POH/IOH/ rebuilding.

·         Clean nose compartment air filter every month & replace filter in M4 and above schedules.

·         Test bench checking of magnet valves.

·         Training of minor schedule electrical staff on tell tale sign of malfunctioning of power contactor on sluggish operation, variable application timing, presence of oil in air and inadequate air pressure.

OVERHAULING PROCEDURE OF MAGNET VALVE

1.    Magnet valve overhauling to be done in M24 Sch and above.

2.    After dismantling, clean all spares with Orion/petrol and compressed air to upper & lower interior and valve seat.

3.    Check operating coil resistance and conduct inter turn short circuit test.

4.    Visually check inlet valve, exhaust valve, spring etc for sign of damage corrosion and pitting.

5.    If any groove is observed in mating face, lapping of both the valves are to be done with lapping paste in lapping machine.

6.    During assembly, replace rubber shim to tighten the op. coil.

7.    Replace nylon washer under the plug.

8.    If spring is found short in length or having less stiffness, it should be replaced.

9.    Check armature stop at corner point using magnifying glass for any crack.

10. Fit armatures stop mounting screws with proper spring washer and seal it with a MS thin strip so that if loosened, should not drop on run.

11. Test m/valve with 5 kg/sq. Cm. air pressure. No air should leak from exhaust port or anywhere.     

 (Foam or soap with water can be used for the purpose)

12. Operate coil with 72 v DC supply and check. Air should come through outlet port only.

 If leakage is observed, rework is required.

NB- * Care should be taken to avoid mixing of valves.

·  Also care should be taken during fitment in loco, to ensure proper seating of rubber O ring. 

NB- shed should strive to replace Magnet Valves assuming 10 years life of magnet valves.

Sub:- Testing of capacitors.

         

          Proper testing of capacitor is essential for ensuring reliable performance of capacitors.

 EC1 & EC 2 capacitors in the stabilisation circuit are critical and if not replaced regularly, may lead to loco failure.

          Whenever, panels need schedule inspection, following steps would lead to better performance of capacitors.

a.      Measurement of parameters by a calibrated instrument.

b.      Confirming critical parameters as per technical specification.

c.      Replacing capacitors in regular intervals.

d.      Life of the capacitor: Normally, life of capacitors is between 3-4 years. It has been observed the Capacitors are not changed in regular intervals of time.

e.      Critical Parameters: Quality of the capacitor can’t be ascertained by simply measuring Capacitance. Other important parameters to be checked are the measurement of Power Factor, ESR(equivalent series resistance), Leakage current and Voltage Buildup.

f.       Instruments to be used for measurement are

I     Capacitance meter

II    Leakage current tester

g.      Technical specification and Test procedure for electrolytic capacitors are mentioned at Annexure-A. Procedure as laid down should also be referred in addition to BHEL maintenance practice.

h.     It is requested to organize technical audit of Capacitor testing and checking procedure in Diesel shed in consultation with OEM.

Technical specification for electrolytic capacitors with casing of heavy duty moulded phenolic with integral safety valve and temperature range of -25 o C to + 85 o C:

Type of  capacitors	Capacitance ©	Working voltage	Tolerance	Leakage current	Power factor	Surge
100 ufd/250 VDC(non polar)	100 ufd	250 VDC	-10% to +25%	0.03 CV + 20 uA or 4 mA whichever is less	15% max	400 volts
500 ufd/125(non polar)	500 ufd	125 VDC	-10% to +25%	0.03 CV + 20 uA or 4 mA whichever is less	15% max	200 volts
1000 ufd     ( polar)	1000 ufd	150/200 VDC	-10% to +50%	0.03 CV + 20 uA or 4 mA whichever is less	15% max	200/300 volts
1300 ufd/100VDC    ( polar)	1300 ufd	100/150 VDC	-10% to +50%	0.03 CV + 20 uA or 4 mA whichever is less	15% max	160 volts
1500 ufd  ( polar)	1500 ufd	100/150 VDC	-10% to +50%	0.03 CV + 20 uA or 4 mA whichever is less	15% max	160/200 volts

Note

Surge voltage as per IS standards is 115 times rated voltage. However, considering the application is critical and to improve reliability, the surge voltage is specified in higher side.

          Sub:-  CTRB  & Roller Bearing Maintenance practices.

        Recent failure of Loco No. WDP₄ 20016 due to CTRB, failure has highlighted the need to ensure proper examination of CTRB. 

Trip examination

1.    Predictive maintenance – Measure CTRB temperature of each wheel both ends quickly with non-contact type laser temperature gun.

        Readings are best taken in yard. All readings must be taken quickly at identical location in axle box & it should be checked that temperature readings are not vitiated due to effect of sun on one side of axle box in stationary loco.

        Though practice of temperature recording has been started in sheds, interpretation of result & corrective action is lacking in most of sheds.

2.    Periodical measurement in yard/mainline fueling point should be organized.

3.    O.E.M. recommends change of bearing, when it becomes difficult to touch bearings by hand or if bearing temperature is more than 90⁰ Centigrade.

 As these are limiting rejection criteria and bearings will be irreversibly damaged in line most probably before loco touching the shed, it is necessary to use predictive maintenance technique to predict impending failure before actual failure in line.

4.    Temperature difference across each wheel should not exceed 3-4⁰ C. Temperature difference between any two axle-boxes should not exceed  7-8⁰ C. If excess temperature difference is observed than axle box should be examined for unusual rise in temperature.

5.    During trip examination, under-gear checking staff & wheel gauger should be trained to look for broken back cover bolt, oozing out of grease. Wheel/axle box should be replaced in case of any irregularity  noticed.

6.    If no fault is noticed in shed despite higher temperature difference is obtained, then one staff should be booked in footplate along with temperature gun to record the temperature after 100, 200, 300 km of run. 

7.    If no variation in temperature rise is observed than loco can be permitted to run, if higher variation > 9⁰ C is obtained then wheel requires to be replaced.

Axle box maintenance/ in shed.

1.  Axle box attention is shed should be avoided. CTRB should be sent to workshop for overhauling as per periodicity laid down by O.E.M.(6 years)

2.    No overdue Axle box should be permitted in service. Date of OVH should be painted in axle box cover for case of identification.

3.    Any wear or damage to end cap or packing is an indication that adapter has been out of position & bearing may have sustained damage. Bearings having external parts visibly cracked, damaged or bent must be removed from service.

4.     Wheels must be free from built up deposition trend & several slid flats.

5.    Use temperature indicating acrylic strip/crayon of 90⁰ centigrade; if it is found black then bearing must be removed from service.

Tell tale signs for identifying defective CTRB

1.    Loose backing ring. A backing ring that can be rotated by hand is considered as loose.

2.    Loose, cocked or visibly damaged, grease seal of the cartridge tempered roller bearing.

3.    Missing cap screws or missing locking plate.

4.    Grease leakage between cup counter bore & seal may be an indication of loose seal. Grease leakage between the backing ring & axle fitted radius is an indicator of loose backing ring & must be removed.

5.    RDSO has identified less torque value for tightening axle cap screw as one of the most probable cause of failure. Axle cap screws must be tightened to a torque of 420 ft-lbs. As a special drive all existing EMD locos must be tightened with revised torque value ( RDSO Instruction Bulletin No.MP.IB.VL-08.30.09   (Rev 00).

6.    Mounted end play (MEP) should be measured by using magnetic base dial indicator. If the bearing end play is less than .001” or more than .015 ”. Bearing should be removed.

7.    After conducting UST of axle as per the recommended procedure, apply a new locking plate and tighten all axle cap  screws to a torque value of 420 ft. lbs using a suitable torque wrench which must be accurate within ± 4%.

8.    Check for Noise(Rough Ride Check)

a.    On rotation by hand, the noise produced, if any, should be interpreted as follows:

·         Hissing: Hissing noise is normal. This noise is basically generated due to running of seals on the seal wear ring.

·         Rattling: Rattling noise is also normal.  It is due to hitting of roller to the cage pocket during running.

·         Cyclic: If the noise is cyclic and abnormal, bearing should be removed from service.

9.    Checking proper seating of CTRBs.

It should be checked by inserting a feeler gauge inside the backing ring.           A 0.0025” feeler should not go in.

10.              Adapter examination:

·               Cracked or broken adapters must be scrapped. Repair by weld or brazing is not permitted.

·               Warped, twisted or distorted adapters must be scrapped.

·               Worn Adapters, adapters having groove, not meeting gauge specification must be scrapped.

·               If wear on both sides exceeds 1/8” (3 mm), adapter should not be reused.

                 Shed should identify overdue and defective CTRBs running in service and make an action plan to replace/overhaul them on priority.

Sub – Checking   tappet    clearance and valve timings.

       Recent cases of unusual sound in engine and change in its beat was observed during foot plate inspections (16386 WDM3A  & 16078 WDM3A .

       Tappet clearances were found disturbed during detailed shed investigation.

       The term valve clearance or tappet clearance refers to the "gap" between the cam and the cam follower, or between the top of the valve and the tappet or rocker arm that pushes the valve open. Due to change in tappet clearance engine sounds noisy, rattly , "tappety" or misses its beat . 

       There has to be some free play here as the valve will expand when hot and take up the gap, with disastrous consequences. The valve will not seal correctly and will overheat and burn, while causing pre-ignition, detonation, valve and seat damage and less power

Checking and ensuring correct tappet clearance is essential for proper functioning of engine.

       It is hereby advised to ensure following points during schedule maintenance in shed.

·            Clearance between valve stem and equalizing yoke should be 34 thou (0.034”).

·            Tappet clearance & valve timing should be checked in every M2 and above schedules.

·            If tappet clearance is found less or more than 0.034” then check

o   Thread profile of adjusting screw and self locking nut.

o   Less clearance shows the possibility of loose adjusting screw, coming out of bushing on upper end or thrust ball at lower end of push rod and excess carbon deposition on valves.

o   More tappet clearance also indicates probability of bent push rod/valve/push rod lifter, worn out cam lobe/cam roller/seat push rod or other mating parts.

·               Replacing adjusting screw and self locking nut in M-24 and above schedules.

·               Repeated variation of tappet clearance on particular cylinder head needs to be thoroughly investigated after replacing valve lever assembly and FIP support.

·               Ensure use of thread locking compound on adjusting screws of non adjustable push rod end and valve lever for adjustable end. One round drive should be done in M4 & above schedule.

·               The timing mark must not go out of sight at either the top or bottom of the window.

·               Check fuel pump tappet lift in M-24 and above schedules, it should be 0.101” – 0.118” for 251 B (WDM2, WDM3 or WDG3) and 0107” – 0.090” for 251 D engine (YDM4).

·                Listening of engine sound through engineers’ stethoscope during schedule maintenance. 

·                                             Checking of valve timing and measurement of tappet clearance shall be done as per MI( 11034-C/Tappet & 11032-A/Timing).

·                                             Training of sectional staff should be organised on above.

Pr

Enclo:-Checking of valve timing & tappet clearance procedure.

                        

Checking procedure for tappet clearance and FIP timing:

Following procedure may be followed for checking valve timing and measuring tappet clearance.

Install cylinder head, FIP support and FIP and valve lever mechanism along with push rod (two nos. for each cyl head).

·         Bar the engine over in the direction of rotation (counter clock wise when viewed from generator end) until the timing mark of any one fuel pump spring guide cup is beginning to rise. Continue to bar the engine over until the hole of the generator fan ring coincides with the half hole in the lower portion of the pointer i.e. the point of injection.

·         The piston of this cylinder is approaching top dead center on its compression stroke and is at the correct crank shaft angle. At this position check tappet clearance and timing of that particular cylinder. First set the timing and then tappet clearance in the following process.

·         Fuel pump guide cup should be line in line with the stationary mark on the pump window. If it is not aligned, adjust the timing after loosening lock nut and turn adjusting screw up or down until the mark on the plunger guide cup coincides with the reference mark on the pump housing.

·         After adjusting, bar the engine and watch the timing mark on the guide cup.   The timing mark must not go out of sight at either the top or bottom of the window. If the guide cup line disappears out of the top of window, delivery valve may damage. And if it disappears out of bottom of the window, the snap ring may shear.

·         Check the tappet clearance between valve stem & equalizing yoke at non adjustable end and between valve stem & adjusting screw at adjustable end, if it is found less or more than 0.034” adjustment is required.

·         First adjust non adjustable end, turn the adjusting screw at push rod end of the valve lever until 0.034” feeler can be inserted between the non adjustable end of equalizing yoke and the valve stem. Leave this feeler in place and tighten the lock nut at push rod end, holding the adjusting screw while tightening the lock nut.

·         Without removing feeler from non adjustable end check and adjust clearance between adjusting screw and valve stem of adjustable end by inserting another feeler.

·         Recheck both clearances to make certain that the proper clearance exists on both valves. Continue through the firing order on subsequent cylinders.