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.

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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.