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FOREWORD

This program is designed to teach you the theories and

procedures for setting injectors and valves. We've used

an NH/NT engine model to establish the two most cur-

~ rent methods of overhead adjustment. We'll drscuss the

process for rdentifyrng the differences between PT (type

You'll see howD) and PT (type D) Top Stop injectors.

to use the injector type for determining the correct ad-

justing method

We hope this program provides you with a better under-

standing about how overhead settings affect engine life

and performance

~Produced by:

J. E. MobleyDistribution Training

~ Copyright@ 1983Cummins Engine Company, I nc

1 This program covers the most current in-jector and valve adjustment proceduresfor Cummins NH/NT engine models withPT (type D) Top Stop or non Top Stop

injectors.

2. Shown here are specific valve train re-lated parts. The injectors, push rods,cam followers, rocker levers, crossheadsand valves are commonly referred to asthe overhead.

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3 We'll discuss the theory and proceduresfor setting injector plunger travel usingthe dial indicator method (D.I.M. ) .

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4. Included is the recommended procedurefor checking and adjusting crossheads.We'll discuss the effects of crosshead ad-justment related to valve operation.

5 This is a Top Stop adjustment fixture(3375160). It's required to set Top Stopplunger travel, and to torque the splinedlocknut to 55 ft.lbs. The plunger travelis set by preloading the injector springwith the weighted handle at a prescribedtravel.

6. Plunger travel for Top Stop injectorscannot be set in the engine. Always usethe adjustment fixture (3375160) to setTop Stop injector plunger travel. Travelis changed by turning the adjusting nut.The upward travel stops when the sprin-gwasher contacts the nut. The downwardtravel stop is the injector cup.

This program uses an NH/NTright-hand-rotation engirie, firing order1-5-3-6-2-4. We'll fi rst explain pistonmovement relative to cran kshaft rotation .Understanding the relationship of thecrankshaft to firing order will help youidentify injector and valve adjustmentpositions .

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8. Piston movement is actuated by thecrankshaft connecting rod journals. Thetwo upward strokes are compression andexhaust, the downward strokes are in-take and power. In a 4 stroke cycle thetwo pistons traveling together in thesame direction are called companion cyl-inders.

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9 Crankshaft firing order positions areidentified by the valve set marks. Theyare located on the accessory drivepulley. When it is rotated in the di rec-tion of cran kshaft rotation, any "VS"mark A, B, or C may be aligned with thecast-in pointer on the gear cover. Atany "VS" mark the pistons in the cylin-ders to be adjusted are moving upward.Note, when the "TC" or top-center markis aligned, cylinders 1 and 6 are attop-dead-center.

10. Valve set marks are geometrically spacedin accordance with the connecting rodjournals. The journals and marks arespaced 120° apart. This spacing ac-counts for the relationship betweencrank angle degrees and piston travel lo-cations .

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11. The following slides will help you morethoroughly understand how the valve setmarks relate to cran k and piston posi-tions. When the accessory drive is posi-tioned at the "A" mark, cylinders 1 and6 have traveled 900 on their downwardstroke. Remember, the two downwardstrokes are intake and power.,,-.

12. With the "A" mark still at the pointer,cylinders 2 and 5 are 300 before-top-center in an upward stroke position .Notice the cran kshaft rod jou rnals forcylinders .2 and 5 relate to the "8" mark.

The " A ., mark is still aligned with the

pointer. At this time pistons 3 and 4 arepositioned 1500 before-top-center. Theyhave just passed bottom-dead-center be-ginning their upward strokes. Thecrankshaft rod journals for cylinders 3and 4 relate to the "C" mark.

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14. Remember, the valve set marks, A, B,and C relate to the spacing of the crank-shaft connecting rod jou rnals .Each setof cylinders A, B, and C are companioncylinders. When any "VS" mark isaligned, the pistons in the correspondingcylinders to be adjusted are moving up-ward.

15 This circle represents a crankshaft. Itis spaced in degrees which relate to the4 cycles of piston travel. It takes tworevolutions of the cran kshaft, or 720°,to complete a full fuel injection cycle.The circles are incremented to the 2 up-ward strokes, exhaust and compressionand the 2 downward strokes, intake andpower.

16. The "Vs" adjustment marks also serve aspoint locators for the camshaft. The in-jector and valve camshaft lobes have def-inite surface positions. The lobesurfaces are:

INJECTOR.Inner Base.I njection Ramp.Cam Nose.Outer Base.Retraction Ramp

VALVE

.Closing Ramp

.Base Ci rcle

.Opening Ramp

.Pea k Lift

17. Like the relationship of the "V5" marksto the crankshaft rod journals, thesemarks relate in the same manner to theinjector and valve lobes. It takes twocrank revolutions to equal one camshaftrevolution (3600). The marks on the ac-cessory drive indicate the points on thecam lobes where the roller must be posi-tioned to ensure correct overhead

adjustments.

18. When properly aligned, the "VS" markslocate the correct camshaft position thatis requi red for making injector and valveadjustments for all Cummins methods.Cummins NH/NT models produced priorto 1971, and small vees will require thetorque method of overhead set ti ng .However, where the application permits,the D.I.M. camshaft positions are pre-ferred for most models.

19 The torque method of adjustment re-qui res precise alignment of the "VS"marks. The torque adjustment point islocated on the outer-base-circle of theinjector lobe at 900 after-top-center dur-ing the power stroke. If the adjustmentpoint is passed, the valve lobe roller willhave started up the ramp and clearancewill be loose because the exhaust valveswill have started to open .

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20. The dial indicator method uses two sepa-rate adjustment points, both located onthe inner base circle of the camshaftlobes. This method requires that the in-jector and valves be set on separate cyl-inders, the injector at the beginning ofthe compression stroke, the valves at theend of the same stroke on the corre-

sponding cylinder.

Use this drawing to aquaint yourself withthe injector "VS" adjustment point. Theinjector is metering; the plunger is posi-tioned at rts uppermost travel in thecup. The piston is moving upward onthe compression stroke at or near 1500B.T.C. The roller is positioned on theinner base circle of the injector lobe.

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22. The exhaust lobe adjustment point occursat or near 300 B.T.C. near the end ofthe compression stroke. At this positionboth the jntake and exhaust valves areclosed, providihg lash in the valve trainto ensu re correct clearance settings. Ifpositioned past the adjustment point, theintake valves will start to open, causingloose clearance settings.

23 This slide highlights the injector and ex-haust roller-to-lobe positions at the "A"valve set adjustment point. The in-jector lobe is positioned on the innerbase circle, or 1500 B.T.C. The ex-haust valve lobe is positioned prior tothe opening ramp at 30° B.T.C.

This valve lift graph shows the relation-ship between cam lobe positioning andcrank stroke. The exhaust valve is di-rectly related to the power and exhauststrokes. The exhaust valve is closed onthe base circle and is fully open at peaklift. The arrows depict the di rection ofcam roller travel.

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25. This graph illustrates the approximateposition of the exhaust valve adjustmentpoint for any given cylinder. The "VS"point occurs during the compressionstroke, when both the exhaust and in-take valves are closed. Thecrosshatched section represents valveoverlap. During valve overlap bothvalves are slightly open .

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26 We've overlayed an injector profile toprovide you a guide for seeing the re-lationship between intake valve and in-jector travel. Note the relationshipbetween the "VS" adjustment points .The injector roller has just passedB.D.C. The exhaust lobe is nearingT. D. C. Du ring injection both sets ofvalves are closed.

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27 Before we get into setting valves and in-jectors, let's ask- ourselves a question .What determines the setting method?Recognizing the unique parts of the TopStop will provide you the clues. The twomethods are torquing to preload the TopStop plunger link and setting the nonTop Stop plunger travel with the dialindicator.

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28. Top Stop injectors are easily identifiedby the splined locknut on top of the in-jector body. Top Stops are preloaded toproduce a no-lash condition between theplunger link and the rocker lever.

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29. Being able to identify the injector typewill aid you in determining the correctoverhead adjustment procedu res. Withthe Top Stop, the data plate reads T.S.Zero Lash.

30 This injector and valve adjustment tablewill aid you in finding the two cylindersthat are beginning and ending the com-pression stroke. The numbers representthe cylinders to be adjusted when thepointer is aligned with one of the "VS"marks. Adjustment procedures can bemade starting at any "VS'I mark, thenproceeding through the firing order.For example, if the pointer is at II A II ,

check for closed valves on cylinders 5and 2; the injector will be metering on 3or 4.

31 Cummins recommends adjustment be madewhen the engine is cold (1400 or less);because temperature variations acrosscylinders can affect clearances.

32. Use this check to identify the closedvalves. With your thumb and index fin-ger, try to raise and lower the exhaustand intake rocker levers. When both le-vers move, the valves are free fromspring tension. This condition indicates(1) the valves are closed, (2) the cylin-der is on the compression stroke and (3)the companion cylinder valves are open .

If you fail to locate the compressionstroke using the rocker lever check, trythis procedure: Loosen the intake andexhaust adjusting screws 1/2-1 turn;this introduces lash in the valve train .Once again, try the rocker lever check.

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To locate the compression stroke in anengine with newly-installed rockerboxes, follow these procedures: Checkthe torque on the rocker box capscrewsto make sure it's within recommendedspecifications. Then, with the valve setmark " A II aligned, tu rn down the rocker

lever adjusting screws on cylinders 2and 5 to remove all valve lash. Note,any "VS" mark may be aligned and itscorresponding adjusting screws tight-ened.

34.

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r'To determine whether cylinder 2 or 5 ison the compression stroke, observe theheight at which the intake and exhaustadjusting screws protrude above thelocknut. The set of screws that pro-trudes at approximately the same heightidentifies the compression stroke. Theexhaust stroke shows a slightly higherprotrusion on the exhaust adjustingscrew.

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To begin the adjusting procedures, ro-tate the accessory drive in a clockwisedirection. Align the valve set mark "A"with the pointer. CAUTION, be surewhen rotating from the accessory drivethat it has a 3/4" flanged nut;otherwise, rotate from the cran kshaftbecause you may overtorque theold-style nut.

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37 Once again by referencing our valve andinjector adjustment table, we know tocheck for loose rocker levers on 5 and 2.By using the rocker lever test, we findthe valves are closed on 5. Looking atou r table we see plunger travel for thestandard PT (type D) injector should bechecked and set on cylinder number 3.

38. To set plunger travel use service tool kit(3375842). Before setting the injectorplunger travel, check the torque on therocker box housing and injectorhold-down capscrews. When necessary,retorque them to maintain tolerances.

39. To set up the dial indicator, position itin the mounting bracket so that thegauge mounts flush and the extensionmoves freely. Securely tighten the holddown into place in the rocker box hous-ing. Position the extension securely ontop of the injector plunger flange.CAUTION, be sure the extension clearsthe rocker lever.

40. Using the actuator, compress the rock-er lever 2 or 3 times to completely seatthe injector plunger. With the plungerseated, zero the indicator. Slowly releasethe rocker lever. Now, compare the in-dicator reading to the recommendedplunger travel. If the travel is withinplus or minus .001" of the specification,it is not necessary to re-set. CAUTION,injector plunger travel settings vary ac-cording to engine model.

41. If injector plunger travel is out of spec-ification limits, loosen the locknut on theinjector adjusting screw. Compress therocker lever until the plunger is seatedto assure a zero indicator reading. Al-low the plunger to rise, then tu rn thescrew until plunger travel matches thespecification.

42. Hold the adjusting screw in place whileyou tighten the locknut, or plungertravel may be altered during torquing.If threads of adjusting screws are muti-lated or galled, they may not hold ortorque correctly, due to the increasedfriction between metal parts. If you findunacceptable wear conditions on the ad-justing components, replace them.

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43. Torque the(54-61 N.m).

40-45 ft.lbs.locknut to

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44. Note, Cummins service tool ST -669torque wrench adapter can be used tosimultaneously hold the adjusting screwand torque the locknut. CAUTION,when using the ST-669, torque valuesare lower. Torque the locknut to 35-40ft.lbs. (47-54 N.m). Once you've com-pleted th.e torquing procedu re, recheckthe plunger travel reading. If you obtainan inaccurate reading, repeat the adjust-

ing procedure.

45. After setting injector plunger travel,check and set the crossheads and valveclearances on cylinder number 5. Al-ways check the engine data plate andother cu rrent service publications foradjustment specifications .

46. Before we adjust the crossheads andvalves, let's take a moment to reflect onour present valve set mark " A " location .

(1) The valves are closed on cylindernumber 5, (2) The roller is positioned onthe base circle, (3) The piston is travel-ing upward, positioned 300 before-top-center on the compression stroke.

47. To begin the crosshead and valve ad-justment procedu res always check thecrossheads first. The crossheads areexposed here to illustrate that one rock-er lever operates two intake or two ex-haust valves with equal tension. Amisadjusted crosshead causes contactsurface wear, thereby increasing stresson the valve train.

48. To adjust the crossheads, back off theintake and exhaust valve locknuts andadjusting screws. Inspect the crossheadcontact surfaces for wear. Hold thecrosshead in place and lightly turn downthe adjusting screw until you feelcontact. Advance the screw slightly andlock it down .

49. Torque the locknut to 25-30 ft.lbs.(34-41 N.m). Be careful not to turn thescrew; if its position changes, back offthe locknut and screw, and readjust.NOTE: When using the ST -669 TorqueWrench adapter, torque the locknut to22-26 ft.lbs (30-35 N.m).

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50. Valve clearance, or lash, is the spacebetween the crosshead surface and therocker lever. Incorrect clearances affectoverall engine performance, emisson lev-els, and valve train wear. With the en-~ine positioned at the valve set mark

A", set the clearances on cylinder num-ber 5.

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The intake and exhaust valve clearancesdiffer. Check the data plate or shopmanual for correct clearances.

51.

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52. Now insert the feeler gauge between therocker lever and the crosshead contactsurface. With the feeler gauge in place,tighten the adjusting screw until you feelit contact. Advance the screw slightlyand lock it down. This process preventsthe loss of clearance during torquing,and helps to provide consistent clearancesettings throughout the engine. Whenthe gauge is moved you should feel aslight drag .

53. Torque the locknut to 40-45 ft.lbs.(54-61 N.m). When removing the gauge,you should still feel a slight drag. Ifyou do not, repeat the valve clearanceprocedure. Be sure to use the correctclearance specifications.

54. Now rotate the accessory drive in the di-rection of engine rotation to valve setmark "8" and repeat the injector andvalve adjustments. The "8" indicatesthe valves may be set on 3 and the injec-tor on 6. Each valve set mark is usedtwice to set all 6 cylinders .

55 When preloading Top Stop injectors, usethe D.I.M. adjustment points. At thistime, let's take a moment to reflect onour present "Atf valve set mark position.The injector for cylinder number 3 is me-tering and the cam' roller is positionedon the inner base circle.

56. Preloading Top Stop injectors helps toprovide consistent injection timing for all6 cylinders. The process consists oftorquing the injector adjusting screw topreload the link between the plunger andthe rocker lever. ~

57. To perform the adjusting procedure,first loosen the injector adjusting locknutand screw on cylinder number 3.

58. Now tighten the injector adjusting screwuntil all the clearance is removed fromthe injector train. Turn the screw downone additional tu rn to squeeze excess oilfrom the contact surfaces. This proce-dure does not bottom the plunger in thecup., but partially compresses thespring.

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59. Now you are ready to set a 5-6 in.lb.preload on the injector train. To dothis, back out the injector adjustingscrew until you feel the spring washercontact the stop nut. The injector rock-er lever is now unloaded.

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60. Using service tool (3376592), torque theadjusting screw to 5-6 in.lbs. NOTE: Ifthis service tool is not available, use atorque wrench with an in.lb. readingthat does not exceed 12 in.lbs. CAU-TION: An overtorqued setting on theinjector adjusting screw will produce in-creased stress on the injector train.

61. Hold the adjusting screw in place with ascrewdriver and tighten the locknut.Note the position of the screw slot.Torque the locknut to 40-45 ft.lbs.(47-54 N.m) .CAUTION: If the screwposition changed, repeat the procedu re.

62. To adjust the crosshead and valve clear-ances, refer to frames 45 thru 54 forclearance settin~ procedures. Remem-ber, each "VS' mark is used twiceto set all 6 cylinders.

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63. Mechanical variable timed engines useTop Stop injectors. When making over-head adjustments, the actuator must bein a fully retarded mode. To retard,idle the engine and gently disconnect theelectrical wire from the air solenoid.This action depresses the actuator.

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64. MVT models use a special camshaft de-sign. This design requi res that a spe-cia! bolt-on-pointer bracket be used toalign the "VS" marks. The pointer ispositioned 400 clockwise from thepre-cast pointer. CAUTION, do not usethe "TC" marks in reference with thebolt-on-pointer.

65. Correctly adjusted overheads impact onfuel economy, power, emission levels,engine life, and the reliability and dura-bility of engine performance.

The Top Stop design offers several ad-vantages: (1) injector plunger travel ispre-set and does not require setting inthe engine, (2) tests show that plungertravel remains calibrated longer becauseit improves train and joint lubrication,thereby, causing less wear on the cam-shaft and other related parts, and (3)offers improved emission levels .

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67. Misadjusted plunger travel produces anoticeable difference in fuel consump-tion. Travel distances and time contrib-ute to effective meteri ng at the fuelport. Fuel arriving late produces an in-complete burn, which leads to carbon-ing and black smoke.

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68. Improperly torqued preload and/or mis-adjusted plunger travel can also producean excessive load on the cam. Other re-sults are bent push rods, camshaft lobewear due to roller contact fatigue, andhigher particulate and smoke levels.

69. Incorrect crosshead and valve adjustmentaffect engine performance and reliability.Tight valve clearances can cause burntvalves. Loose clearance settings cancause air restrictions, low power, blacksmoke, increased impact loading on thevalve train, and increased overheadnoise levels .

70. Remember, always check overhead set-tings at the recommended scheduledmaintenance intervals for optimum enginelife. Use the prescribed methods per in-jector type and engine model. The injec-tor type designates the method ofoverhead adjustment.

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71 We have thoroughly discussed the theo-ries and procedures for adjusting the PT(type D) Top Stop and non Top Stop in-jectors, as well as the crossheads andvalves. We're confident that each of youhas gained a better understanding ofthese procedures, not only HOW to setthe overhead, but WHY it must be donethis way.

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