.
FOREWORD
This
~
program
is designed
procedures
for
an
engine
NH/NT
rent
methods
setting
of
process
for
D) and
PT (type
We hope
standing and
to
overhead the
D) Top
to use the injector justing
injectors
model
rdentifyrng
to teach
you the theories
and valves.
establish
the
We've
two
adjustment.
We'll
differences
between
Stop injectors.
type for determining
and used
most
cur-
drscuss
the
PT (type
You'll
see how
the correct
ad-
method
this
program
about
provides
how overhead
you
with
settings
a better
affect
under-
engine
life
performance
~ Produced
by:
J. E. Mobley Distribution Training
~
Copyright@ 1983 Cummins Engine
Company,
I nc
1
This program covers the most current injector and valve adjustment procedures for Cummins NH/NT engine models with PT (type D) Top Stop or non Top Stop injectors.
2.
Shown here lated parts. cam followers, and valves the overhead.
3
We'll discuss the theory and procedures for setting injector plunger travel using the dial indicator method (D.I.M. ).
4.
Included is the recommended procedure for checking and adjusting crossheads. We'll discuss the effects of crosshead adjustment related to valve operation.
~ 0,
are specific valve train reThe injectors, push rods, rocker levers, crossheads are commonly referred to as
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2
5
This is a Top Stop adjustment fixture (3375160). It's required to set Top Stop plunger travel, and to torque the splined locknut to 55 ft.lbs. The plunger travel is set by preloading the injector spring with the weighted handle at a prescribed travel.
6.
Plunger travel for Top Stop injectors cannot be set in the engine. Always use the adjustment fixture (3375160) to set Top Stop injector plunger travel. Travel is changed by turning the adjusting nut. The upward travel stops when the sprin-g washer contacts the nut. The downward travel stop is the injector cup.
7.
This program uses an NH/NT right-hand-rotation engirie, firing order 1-5-3-6-2-4. We'll fi rst explain piston movement relative to cran kshaft rotation . Understanding the relationship of the crankshaft to firing order will help you identify injector and valve adjustment positions .
8.
Piston movement is actuated by the crankshaft connecting rod journals. The two upward strokes are compression and exhaust, the downward strokes are intake and power. In a 4 stroke cycle the two pistons traveling together in the same direction are called companion cylinders.
9
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Crankshaft firing order positions are identified by the valve set marks. They are located on the accessory drive pulley. When it is rotated in the di rection of cran kshaft rotation, any "VS" mark A, B, or C may be aligned with the cast-in pointer on the gear cover. At any "VS" mark the pistons in the cylinders to be adjusted are moving upward. Note, when the "TC" or top-center mark is aligned, cylinders 1 and 6 are at top-dead-center.
10. Valve set marks are geometrically spaced in accordance with the connecting rod journals. The journals and marks are spaced 120° apart. This spacing accounts for the relationship between crank angle degrees and piston travel locations .
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11.
,,-.
The following slides will help you more thoroughly understand how the valve set marks relate to cran k and piston positions. When the accessory drive is positioned at the "A" mark, cylinders 1 and 6 have traveled 900 on their downward stroke. Remember, the two downward strokes are intake and power.
12. With the "A" mark still at the pointer, cylinders 2 and 5 are 300 before-topcenter in an upward stroke position . Notice the cran kshaft rod jou rnals for cylinders .2 and 5 relate to the "8" mark.
13.
The
" A ., mark
is still
aligned
with
the
pointer. At this time pistons 3 and 4 are positioned 1500 before-top-center. They have just passed bottom-dead-center beginning their upward strokes. The crankshaft rod journals for cylinders 3 and 4 relate to the "C" mark.
14.
Remember, the valve set marks, A, B, and C relate to the spacing of the crankshaft connecting rod jou rnals .Each set of cylinders A, B, and C are companion cylinders. When any "VS" mark is aligned, the pistons in the corresponding cylinders to be adjusted are moving upward.
15
This circle represents a crankshaft. It is spaced in degrees which relate to the 4 cycles of piston travel. It takes two revolutions of the cran kshaft, or 720°, to complete a full fuel injection cycle. The circles are incremented to the 2 upward strokes, exhaust and compression and the 2 downward strokes, intake and power.
16.
The "Vs" adjustment marks also serve as point locators for the camshaft. The injector and valve camshaft lobes have definite surface positions. The lobe surfaces are: INJECTOR .Inner Base .I njection Ramp .Cam Nose .Outer Base .Retraction Ramp
VALVE .Closing Ramp .Base Ci rcle .Opening .Pea k
Ramp Lift
17.
Like the relationship of the "V5" marks to the crankshaft rod journals, these marks relate in the same manner to the injector and valve lobes. It takes two crank revolutions to equal one camshaft revolution (3600). The marks on the accessory drive indicate the points on the cam lobes where the roller must be positioned to ensure correct overhead adjustments.
18. When properly aligned, the "VS" marks locate the correct camshaft position that is requi red for making injector and valve adjustments for all Cummins methods. Cummins NH/NT models produced prior to 1971, and small vees will require the torque method of overhead set ti ng . However, where the application permits, the D.I.M. camshaft positions are preferred for most models.
19
The torque method of adjustment requi res precise alignment of the "VS" marks. The torque adjustment point is located on the outer-base-circle of the injector lobe at 900 after-top-center during the power stroke. If the adjustment point is passed, the valve lobe roller will have started up the ramp and clearance will be loose because the exhaust valves will have started to open .
20.
The dial indicator method uses two separate adjustment points, both located on the inner base circle of the camshaft lobes. This method requires that the injector and valves be set on separate cylinders, the injector at the beginning of the compression stroke, the valves at the end of the same stroke on the corre-
~
sponding
cylinder.
21
Use this drawing to aquaint yourself with the injector "VS" adjustment point. The injector is metering; the plunger is positioned at rts uppermost travel in the cup. The piston is moving upward on the compression stroke at or near 1500 B.T.C. The roller is positioned on the inner base circle of the injector lobe.
22.
The exhaust lobe adjustment point occurs at or near 300 B.T.C. near the end of the compression stroke. At this position both the jntake and exhaust valves are closed, providihg lash in the valve train to ensu re correct clearance settings. If positioned past the adjustment point, the intake valves will start to open, causing loose clearance settings.
23
This slide highlights the injector and exhaust roller-to-lobe positions at the "A" valve set adjustment point. The injector lobe is positioned on the inner base circle, or 1500 B.T.C. The exhaust valve lobe is positioned prior to the opening ramp at 30° B.T.C.
24. This
valve lift graph shows the relationship between cam lobe positioning and crank stroke. The exhaust valve is directly related to the power and exhaust strokes. The exhaust valve is closed on the base circle and is fully open at peak lift. The arrows depict the di rection of cam roller travel.
6
25.
This graph illustrates the approximate position of the exhaust valve adjustment point for any given cylinder. The "VS" point occurs during the compression stroke, when both the exhaust and intake valves are closed. The crosshatched section represents valve overlap. During valve overlap both valves are slightly open .
26
We've overlayed an injector profile to provide you a guide for seeing the relationship between intake valve and injector travel. Note the relationship between the "VS" adjustment points . The injector roller has just passed B.D.C. The exhaust lobe is nearing T. D. C. Du ring injection both sets of valves are closed.
27
Before we get into setting valves and injectors, let's ask- ourselves a question . What determines the setting method? Recognizing the unique parts of the Top Stop will provide you the clues. The two methods are torquing to preload the Top Stop plunger link and setting the non Top Stop plunger travel with the dial indicator.
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28. Top Stop injectors are easily identified by the splined locknut on top of the injector body. Top Stops are preloaded to produce a no-lash condition between the plunger link and the rocker lever. -
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29.
Being able to identify the injector type will aid you in determining the correct overhead adjustment procedu res. With the Top Stop, the data plate reads T.S. Zero Lash.
30 This
injector and valve adjustment table will aid you in finding the two cylinders that are beginning and ending the compression stroke. The numbers represent the cylinders to be adjusted when the pointer is aligned with one of the "VS" marks. Adjustment procedures can be made starting at any "VS'I mark, then proceeding through the firing order. For example, if the pointer is at IIA II ,
check for closed valves on cylinders 5 and 2; the injector will be metering on 3 or 4.
31
Cummins recommends adjustment when the engine is cold (1400 because temperature variations cylinders can affect clearances.
be made or less); across
32.
Use this check to identify the closed valves. With your thumb and index finger, try to raise and lower the exhaust and intake rocker levers. When both levers move, the valves are free from spring tension. This condition indicates (1) the valves are closed, (2) the cylinder is on the compression stroke and (3) the companion cylinder valves are open .
If you fail to locate the compression stroke using the rocker lever check, try this procedure: Loosen the intake and exhaust adjusting screws 1/2-1 turn; this introduces lash in the valve train . Once again, try the rocker lever check.
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34. To ~
locate the compression stroke in an engine with newly-installed rocker boxes, follow these procedures: Check the torque on the rocker box capscrews to make sure it's within recommended specifications. Then, with the valve set mark " A II aligned, tu rn down the rocker lever adjusting screws on cylinders 2 and 5 to remove all valve lash. Note, any "VS" mark may be aligned and its corresponding adjusting screws tightened.
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To determine whether cylinder 2 or 5 is on the compression stroke, observe the height at which the intake and exhaust adjusting screws protrude above the locknut. The set of screws that protrudes at approximately the same height identifies the compression stroke. The exhaust stroke shows a slightly higher protrusion on the exhaust adjusting screw.
To begin the adjusting procedures, rotate the accessory drive in a clockwise direction. Align the valve set mark "A" with the pointer. CAUTION, be sure when rotating from the accessory drive that it has a 3/4" flanged nut; otherwise, rotate from the cran kshaft because you may overtorque the old-style nut. ('
37
Once again by referencing our valve and injector adjustment table, we know to check for loose rocker levers on 5 and 2. By using the rocker lever test, we find the valves are closed on 5. Looking at ou r table we see plunger travel for the standard PT (type D) injector should be checked and set on cylinder number 3.
38.
To set plunger travel use service tool kit (3375842). Before setting the injector plunger travel, check the torque on the rocker box housing and injector hold-down capscrews. When necessary, retorque them to maintain tolerances.
39. To set up the
dial indicator, position it in the mounting bracket so that the gauge mounts flush and the extension moves freely. Securely tighten the hold down into place in the rocker box housing. Position the extension securely on top of the injector plunger flange. CAUTION, be sure the extension clears the rocker lever.
40.
Using the actuator, compress the rocker lever 2 or 3 times to completely seat the injector plunger. With the plunger seated, zero the indicator. Slowly release the rocker lever. Now, compare the indicator reading to the recommended plunger travel. If the travel is within plus or minus .001" of the specification, it is not necessary to re-set. CAUTION, injector plunger travel settings vary according to engine model.
41.
If injector plunger travel is out of specification limits, loosen the locknut on the injector adjusting screw. Compress the rocker lever until the plunger is seated to assure a zero indicator reading. Allow the plunger to rise, then tu rn the screw until plunger travel matches the specification.
42.
Hold the adjusting screw in place while you tighten the locknut, or plunger travel may be altered during torquing. If threads of adjusting screws are mutilated or galled, they may not hold or torque correctly, due to the increased friction between metal parts. If you find unacceptable wear conditions on the adjusting components, replace them.
43.
Torque the (54-61 N.m).
44.
Note, Cummins service tool ST -669 torque wrench adapter can be used to simultaneously hold the adjusting screw and torque the locknut. CAUTION, when using the ST-669, torque values are lower. Torque the locknut to 35-40 ft.lbs. (47-54 N.m). Once you've completed th.e torquing procedu re, recheck the plunger travel reading. If you obtain an inaccurate reading, repeat the adjust-
~
locknut
to
40-45
ft.lbs.
'"""'
ing
procedure.
45.
After setting injector plunger travel, check and set the crossheads and valve clearances on cylinder number 5. Always check the engine data plate and other cu rrent service publications for adjustment specifications .
46.
Before we adjust valves, let's take our present valve
the crossheads and a moment to reflect on set mark " A " location .
(1) The valves are closed on cylinder number 5, (2) The roller is positioned on the base circle, (3) The piston is traveling upward, positioned 300 beforetop-center on the compression stroke.
47.
To begin the crosshead and valve adjustment procedu res always check the crossheads first. The crossheads are exposed here to illustrate that one rocker lever operates two intake or two exhaust valves with equal tension. A misadjusted crosshead causes contact surface wear, thereby increasing stress on the valve train.
48.
To adjust the crossheads, back off the intake and exhaust valve locknuts and adjusting screws. Inspect the crosshead contact surfaces for wear. Hold the crosshead in place and lightly turn down the adjusting screw until you feel contact. Advance the screw slightly and lock it down .
49.
Torque the locknut to 25-30 ft.lbs. (34-41 N.m). Be careful not to turn the screw; if its position changes, back off the locknut and screw, and readjust. NOTE: When using the ST -669 Torque Wrench adapter, torque the locknut to 22-26 ft.lbs (30-35 N.m).
50.
Valve clearance, or lash, is the space between the crosshead surface and the rocker lever. Incorrect clearances affect overall engine performance, emisson levels, and valve train wear. With the en~ine positioned at the valve set mark A", set the clearances on cylinder number 5.
51.
The intake and exhaust valve clearances differ. Check the data plate or shop manual for correct clearances.
52.
Now insert the feeler gauge between the rocker lever and the crosshead contact surface. With the feeler gauge in place, tighten the adjusting screw until you feel it contact. Advance the screw slightly and lock it down. This process prevents the loss of clearance during torquing, and helps to provide consistent clearance settings throughout the engine. When the gauge is moved you should feel a slight drag .
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53.
Torque the locknut to 40-45 ft.lbs. (54-61 N.m). When removing the gauge, you should still feel a slight drag. If you do not, repeat the valve clearance procedure. Be sure to use the correct clearance specifications.
54.
Now rotate the accessory drive in the direction of engine rotation to valve set mark "8" and repeat the injector and valve adjustments. The "8" indicates the valves may be set on 3 and the injector on 6. Each valve set mark is used twice to set all 6 cylinders .
55
When preloading Top Stop injectors, use the D.I.M. adjustment points. At this time, let's take a moment to reflect on our present "Atf valve set mark position. The injector for cylinder number 3 is metering and the cam' roller is positioned on the inner base circle.
56.
Preloading Top Stop injectors helps to provide consistent injection timing for all 6 cylinders. The process consists of torquing the injector adjusting screw to preload the link between the plunger and the rocker lever. ~
57. To perform the adjusting procedure, first loosen the injector adjusting locknut and screw on cylinder number 3.
58.
Now tighten the injector adjusting screw until all the clearance is removed from the injector train. Turn the screw down one additional tu rn to squeeze excess oil from the contact surfaces. This procedure does not bottom the plunger in the cup., but partially compresses the spring.
59.
Now you are ready to set a 5-6 in.lb. preload on the injector train. To do this, back out the injector adjusting screw until you feel the spring washer contact the stop nut. The injector rocker lever is now unloaded.
60.
Using service tool (3376592), torque the adjusting screw to 5-6 in.lbs. NOTE: If this service tool is not available, use a torque wrench with an in.lb. reading that does not exceed 12 in.lbs. CAUTION: An overtorqued setting on the injector adjusting screw will produce increased stress on the injector train.
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61.
Hold the adjusting screw in place with a screwdriver 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 screw position changed, repeat the procedu re.
62.
To adjust the crosshead and ances, refer to frames 45 clearance settin~ procedures. ber, each "VS' mark is to set all 6 cylinders.
valve clearthru 54 for Rememused twice
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63. Mechanical variable timed engines use Top Stop injectors. When making overhead adjustments, the actuator must be in a fully retarded mode. To retard, idle the engine and gently disconnect the electrical wire from the air solenoid. This action depresses the actuator. ~
64.
MVT models use a special camshaft design. This design requi res that a specia! bolt-on-pointer bracket be used to align the "VS" marks. The pointer is positioned 400 clockwise from the pre-cast pointer. CAUTION, do not use the "TC" marks in reference with the bolt-on-pointer.
65.
Correctly adjusted overheads impact on fuel economy, power, emission levels, engine life, and the reliability and durability of engine performance.
66. The
Top Stop design offers several advantages: (1) injector plunger travel is pre-set and does not require setting in the engine, (2) tests show that plunger travel remains calibrated longer because it improves train and joint lubrication, thereby, causing less wear on the camshaft and other related parts, and (3) offers improved emission levels .
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67. Misadjusted plunger travel produces a noticeable difference in fuel consumption. Travel distances and time contribute to effective meteri ng at the fuel port. Fuel arriving late produces an incomplete burn, which leads to carboning and black smoke. /"""
68.
Improperly torqued preload and/or misadjusted plunger travel can also produce an excessive load on the cam. Other results are bent push rods, camshaft lobe wear due to roller contact fatigue, and higher particulate and smoke levels.
69.
Incorrect crosshead and valve adjustment affect engine performance and reliability. Tight valve clearances can cause burnt valves. Loose clearance settings can cause air restrictions, low power, black smoke, increased impact loading on the valve train, and increased overhead noise levels .
70.
Remember, always check overhead settings at the recommended scheduled maintenance intervals for optimum engine life. Use the prescribed methods per injector type and engine model. The injector type designates the method of overhead adjustment.
71
We have thoroughly discussed the theories and procedures for adjusting the PT (type D) Top Stop and non Top Stop injectors, as well as the crossheads and valves. We're confident that each of you has gained a better understanding of these procedures, not only HOW to set the overhead, but WHY it must be done this way.
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