Principles
To provide the necessary alignment between the diesel engine and all mechanically dri-ven components, an understanding of the types of misalignment and the methods of measurement is required.
Many crankshaft and bearing failures are the result of improper alignment of drive
systems at the time of initial engine instal-lation. Misalignment always results in
some type of vibration or stress loading.
CAUTION: BEFORE MAKING ANY ATTEMPTS TO MEASURE RUN OUT OR
ALIGNMENT, IT IS IMPORTANT THAT ALL SURFACES TO BE MEASURED OR MATED BE COMPLETELY CLEAN AND FREE FROM GREASE, PAINT, OXIDA-TION, OR RUST AND DIRT — ALL OF WHICH CAN CAUSE INACCURATE MEA-SUREMENTS.
Common mistakes include failure to detect “run out” of rotating assemblies and paral-lel or angular misalignment of the engineand driven machine.
The run out of a hub or flywheel can be measured by turning the part in question
while measuring from any stationary point to the surface being checked. This can be
done with a dial indicator. Note: Measure to the pilot surface being used, not to an
adjacent surface, because surfaces not used for pilots normally are not machined
as closely.
This check should be made first on the face of the wheel or hub, as illustrated in
Figure 1. Whenever making a face check, make sure the shaft end play does not
change as you rotate it. The crankshaft must be moved within the diesel engine to
remove all end play and that position must be maintained throughout the alignment
procedures.
Checking Face Run Out
While turning the wheel 360°, note any change in the dial indicator reading. Anychange is caused by face run out. Face run out may be caused by foreign
material between a crankshaft flange and flywheel, uneven torquing or from machining variations.
“Cocking” of the wheel being measured may cause indications of outside diameter
run out in addition to face run out. For this reason the face run out is checked first.
After the face run out has been eliminated, outside diameter run out can be checked.
This must also be done with a dial indicator.(See Figure 2.(
Checking Outside Diameter Run Out
While turning the hub through 360°of rotation, check for any change in indicator reading. The indicator is held stationary and, if the reading changes, the outside
diameter is off center.
After the flywheel or driving hub has been checked for run out, the same procedure
should be followed on the driven side of the coupling.
After the run out of both the driving and driven sides of the coupling have been found within limits, the engine and load alignment can be checked. There are two kinds of misalignment: parallel and angular (bore and face). (See Figure 3).
Checking Parallel Alignment
Parallel misalignment can be detected by attaching a dial indicator, as shown in Figure 4, and observing the dial indicator readings at several points around the out-
side diameter of the flywheel as the wheel holding the indicator is turned.
As a rule of thumb, the load shaft should indicate to be higher than the engine shaft
because:
A-Engine bearings have more clearance than most bearings on driven equipment.
B-The flywheel or front drive rotates in a“drooped” position below the center-line of rotation.
C-The vertical thermal growth of the engine is usually more than that of the driven equipment. Engine main bearing clearance should be considered when adjusting for parallel alignment.
Note: Both parts can be rotated together if desired. This would eliminate any out-of- roundness of the parts from showing up in the dial indicator reading. In most cases rubber driving elements must be removed or disconnected on one end during alignment since they can give false parallel readings.
Checking Angular Alignment
Angular misalignment can be determined by measuring between the two parts to be
joined. The measurement can be easily made with a feeler gauge, and it should be the same at four points around the hubs Figure 5.
If the coupling is installed, a dial indicator from one face to the other will indicate any angular misalignment. In either case, the readings will be influenced by how far from the center of rotation the measurement is made.
Note: the face and bore alignment affect each other. Thus, the face alignment should be rechecked after the bore alignment and vice versa.
After determining that the engine and load are in alignment, the crankshaft end play
should be checked to see that bolting and coupling together does not cause end thrust.
Torque Reaction
The tendency of the engine to twist in the opposite direction of shaft rotation and the
tendency of the driven machine to turn in the direction of shaft rotation is torque reaction. It naturally increases with load and may cause a torque vibration. This type of vibration will not be noticeable at idle but will be felt with load. This usually is caused by a change in alignment due to insufficient base strength allowing excessive base deflection under torque reaction load. This has the effect of introducing a side to side centerline offset which disappears when the engine is idled (unloaded)
or stopped.
Belt and Chain Drives
Belt and chain drives may also cause the engine or driven machine to shift or change
position when a heavy load is applied.
Belts and chains may also cause PTO shaft or crankshaft deflection, which can cause bearing failures and shaft bending failures. The driving sprocket or pulley must always be mounted as close to the supporting bearing as possible. Side load limits must not be exceeded. Sometimes, due to heavy side load, it is necessary to provide additional support for the driving pulley or sprocket. This can be done by providing a separate shaft which is supported by a pillow block bearing on each side of the pulley or sprocket. This shaft can then be driven by the engine or clutch through an appropriate coupling.
The size of the driving and driven sprockets or pulleys is also important. A larger pulley or sprocket will give a higher chain or belt speed. This allows more horsepower to be transmitted with less chain or belt tension.
If it is suspected that the engine or the driven machine is shifting under load, it can
be checked by measuring from a fixed point with a dial indicator while loading and unloading the engine. Torque reactive vibrations or torque reactive misalignment
will always occur under load.
Couplings
A coupling must be torsionally compatible with engine and driven load so that torsional vibration amplitudes are kept within acceptable limits. A mathematical study
called a torsional vibration analysis should be done on any combination of engine drive-line-load for which successful experience doesn’t already exist. A coupling with the wrong torsional stiffness can cause serious damage to engine or driven equipment.
All couplings have certain operating ranges of misalignment, and the manufacturers
should be contacted for this information.
Some drives, such as U-joint couplings, have different operating angle limits for different speeds.
As a general rule, the angle should be the same on each end of the shaft. (See Figure6.) The yokes must be properly aligned and sliding spline connections should move freely. If there is no angle at all, the bearings will brinell due to lack of movement.
ALIGNMENT INSTRUCTIONS
General Considerations
Alignment methods will vary depending on the coupling method selected. On Caterpillar Diesel Engines either a flexible-type or rigid-type coupling is acceptable, depending on the specific installation characteristics and the results of the Torsional Analysis.
CAUTION: IT IS IMPORTANT THAT THEPACKAGE ALIGNMENT BE CARRIED OUT AND COMPLETED WITHIN THE PERMISSIBLE TOLERANCES OF THE DRIVEN EQUIPMENT MANUFACTURER.
Alignment Instructions — Single-Bearing Driven Equipment
A. Flexible-Type Couplings — Flywheel
Housing-Mounted Driven Equipment
1-Droop
Mount a dial indicator on the engine flywheel housing. Mark the engine flywheel housing. Mark the flywheel at points A, B, C, and D in 90°increments as shown in Figure 7. The indicator tip must contact the pilot diameter of the flywheel assembly.
With the dial indicator in position (A), set the reading to zero. Place a pry bar under the flywheel assembly at position (C) and, by prying against a floor mounted support, raise the flywheel until it is stopped by the main bearings. (Caution: Do not pry against the flywheel housing.) Record the reading of the dial indicator. This is the amount of droop in the crankshaft, which results from engine bearing clearances and natural droop as a result of the overhung weight of the flywheel. The flywheel should be raised several times to get a “feel” for the bearing clearance to prevent excessive lift which means reverse bending of the crankshaft.
2-Flywheel Concentricity
Remove the pry bar and check to ensure that the dial indicator has returned to zero. If not, reset. Rotate the crankshaft, in the normal direction only, and record the Total Indicator Reading (TIR) when the flywheel positions (A), (B), (C), and (D) are at the top. (Refer to Page 58 for proper tolerances).
3-Crankshaft End Play
Ensure the crankshaft-flywheel assembly is completely to the rear- most position of the engine assembly. Reset the dial indicator to zero.
Relocate the pry bar and move crankshaft-flywheel assembly forward in the engine assembly. The dial indicator reading in this position is the crankshaft end play.
4-Flywheel Face Run Out
Set the tip of the indicator on the face of the flywheel Figure 8. Position the crankshaft to the front of its end play and zero the indicator. Shift the crankshaft to the rear of its end play, and record the TIR. With the crankshaft to the rear of its end play, zero the indicator.
Rotate the crankshaft and record the TIR when the flywheel positions (A), (B), (C), and (D) are at the top. Be sure to remove the crankshaft end play before recording these readings. Remove the flywheel housing access cover and place a pry bar between the rear face of the flywheel housing and the front face of the flywheel assembly. Move the crankshaft flywheel assembly to the rear of the engine to remove all end play.
5-Flywheel Housing Concentricity
Mount the dial indicator on the flywheel assembly with the tip located on the pilot bore of the flywheel housing and set the reading to zero.
Rotate the crankshaft in the direction of normal engine rotation and record the indicator readings at positions (A),(B), (C), and (D).
Subtract the droop dimension (Step 1) from the reading indicated at position (C) and subtract one-half the droop dimension from the reading indicated at positions (B)and (D) on the flywheel housing to determine the true concentricity.
6-Engine Mounting Face Depth
With the crankshaft-flywheel assembly moved to the frontmost position, place a straight edge across the mounting face of the flywheel housing, from position (A) to (C). With a scale measure the distance from the rear face of the flywheel housing to
the coupling mounting face of the flywheel as shown in Figure 9.
Repeat the same measurement with the straight edge located on positions (B) and (D).
Steps 1 through 6 establish the engine tolerances. The following Steps, 7 and
,8determine the driven equipment tolerances or refer to manufacturers specifications.
7-Support the driven equipment
input shaft until it is centered (all droop is removed).
8- Driven Equipment Mounting FaceDepth
With the driven equipment mounting and driving flange or face centered, as described in Step 7, and the flexible coupling attached to the input shaft, the face depth can be measured. Place a straight edge across the surface of the front face of the coupling which mates to the flywheel assembly. With a scale measure the distance from the coupling mounting face to the mounting face of the driven equipment housing as shown in Figure 10.
This dimension must equal the engine mounting face depth Step 6 less one-half of the crankshaft end play as described in Step 4. If not, it must be corrected by changing the adapting parts, or by shimming if the required correction is small. Shimming is usually the less desirable approach.
With the engine and driven equipment tolerances known, proceed to mount the driven equipment to the engine.
9-Support the driven machine on a hoist and bring it into position with the engine.
10-Align the driven equipment housing mounting flange with the flywheel housing, using locating dowels if required. Install connecting bolts with sufficient torque to compress the lock washers, but not to final torque.
11-Install the bolts which secure the coupling to the flywheel and torque as recommended.
12-Check crankshaft end play to ensure that the proper relationship exists between the engine mounting face depth Step 6 and the driven equip- ment mounting face depth Step 8.
Place a pry bar between the flywheel assembly and the flywheel housing.
The crankshaft should move both for ward and backward within the engine
and, in both positions, remain fixed when pressure on the pry bar is relaxed. Any tendency of the crankshaft to move when pry bar pressure is released indicates that the driven equipment and coupling assembly are imposing a horizontal force on the crankshaft, which will result in thrust bearing failure. If this condition exists, readjust the thickness of shims used between the driven equipment input shaft and the coupling as described in Step 8.
13-Determine quantity and thickness of shims required between the driven equipment mounting pads and the base assembly; locate the shim packs and install driven equipment mounting bolts to the base assembly.
NOTE: Always use metal shims. Tighten the bolts to one-half the torque recommendation.
14-Loosen the bolts holding the driven equipment housing to the flywheel housing until the lock washers move freely. Using a feeler gauge, check the clearance between the two housings to determine if the driven equipment is properly shimmed.
Measurement should be made in four 90°increments in the vertical and horizontal planes. If the feeler gauge indicates any area where the clearance varies by more than 0.005 in (0.13mm),readjust the driven equipment housing position by changing the shims.
There must be clearance at all points when making this check.
15-With the proper number of shims installed to align the driven equipment housing parallel to the flywheel housing, tighten the bolts securing the driven equipment housing to the flywheel housing sufficiently to compress the lock washers.
16-Torque the bolts holding the driven equipment frame to the base assembly to one-half the recommended value.
17-Repeat Step 14. If the feeler gauge measurements indicate that misalign-
ment is still present, repeat operation described in Steps 14 through 17 until proper alignment is obtained.
18-Retorque all coupling and mounting bolts to the specified torque value.
B. Flexible-Type Couplings — Remote-Mounted Driven Equipment
1-Droop
Mount a dial indicator on the engine flywheel housing. Mark the flywheel at points A, B, C, and D in 90°increments as shown in Figure 36. The indicator tip must contact the pilot diameter of the flywheel assembly.
With the dial indicator in position (A),set the reading to zero. Place a pry bar under the flywheel assembly at position (C) and, by prying against a floor mounted support, raise the flywheel until it is stopped by the main bearings. (Caution: Do not pry against the flywheel housing.) Record the reading of the dial indicator. This is the amount of droop in the crankshaft which results from engine bearing clearances and natural droop as a result of the overhung weight of the flywheel.
The flywheel should be raised several times to get a “feel” for the bearing clearance to prevent excessive lift which means reverse bending of the crankshaft.
2-Flywheel Concentricity
Remove the pry bar and check to ensure that the dial indicator has re- turned to zero; if it is not, reset. Rotate the crankshaft, in the normal direction only, and record the TIR when the flywheel positions (A), (B), (C),and (D) are at the top.
3-Crankshaft End Play
Ensure the crankshaft-flywheel assembly is completely to the rearmost position of the engine assembly. Reset the dial indicator to zero. Relocate the pry bar and move crankshaft-flywheel assembly forward in the engine assembly. The dial indicator reading in this position is the crankshaft end play.
4-Flywheel Face Run out
Set the tip of the indicator on the face of the flywheel Figure 36. Position the crankshaft to the front of its end play and zero the indicator. Shift the crankshaft to the rear of its end play and record the TIR. With the crankshaft at the rear of its end play, zero the indicator. Rotate the crankshaft and record the TIR when the flywheel positions (A), (B), (C), and (D) are at the top. Remove all end play before recording each reading. Remove the flywheel housing access cover. Then place a pry bar between the rear face of the flywheel housing and the front of the flywheel assembly.
Move the crankshaft-flywheel assembly to the rear of the engine, removing all end play.
5- Mounting
The engine and the driven equipment should be mounted so that any necessary shimming is applied to the driven equipment. The centerline of the engine crankshaft should be lower than the centerline of the driven equipment by approximately 0.0065 in (0.165mm) to allow for thermal expansion of the engine. The value 0.0065 in(0.165mm)allowed for thermal expansion is for the engine only. If it is anticipated that thermal expansion will also affect the driven equipment centerline to mounting plane distance, that value must be subtracted from the engine thermal expansion value in order to establish the total engine centerline to driven equipment centerline distance. When measuring this value, the TIR will be 0.013in plus the droop as estab lished in Step 1.
Shim packs under all equipment should be 0.200 in (5 mm) minimum thickness to provide for later correc- tions which might require the removal of shims.
6-Coupling
Attach the driven member of the coupling to the flywheel and tighten all bolts to the specified torque value.
Gear-type couplings, double sets of plate-type rubber block drives, and Cat viscous-damped couplings are the only ones that can be installed prior to making the alignment check. Most couplings are stiff enough to affect the bore alignment and give a false reading.
7-Angular Alignment
Mount a dial indicator to read between the driven equipment input flange and the flywheel face and measure angular misalignment. Adjust position of driven equipment until TIR is within 0.008 in.
8-Linear Relationship
Mount dial indicator to the driven equipment side of the flexible coupling and indicate on the outside diameter of the flywheel side of the coupling. Zero the indicator at 12 o’clock and rotate the engine in its normal direction of rotation and check the total indicator reading at every 90°. Subtract the full“droop” from the bottom reading to give the corrected alignment reading.
The value of the top-to-bottom reading should be 0.008 in (0.20 mm) or less
under operating temperature conditions, with the engine indicating low.
Adjust all shims under the feet of the driven equipment the same amount
to obtain this limit.
The final value of the top-to-bottom alignment should include a factor for
vertical thermal growth.
Subtract one-half the “droop” from the 3 o’clock and 9 o’clock reading. This
should be 0.008 in (0.20 mm) or less.
Shift the driven equipment on the mounts until this limit is obtained.
Note: the sum of the side “raw” reading should equal the bottom reading within
0.002 in (0.051 mm). Otherwise the mounting of the dial indicator is too weak to support the indicator weight.
9-The combined difference or readings
at points B and D should not exceed a total of 0.008 in (0.20 mm). (SeeFigure 12).
10-Crankshaft End Play
The crankshaft end play must be rechecked to ensure that the driven equipment is not positioned in a manner which imposes a preload on the crankshaft thrust washers. (Refer to Step 4.) Place a pry bar between the flywheel assembly and the flywheel housing. The crankshaft should move both forward and backward within the engine and, in both positions, remain fixed when pressure on the pry bar is relaxed. Any tendency of the crankshaft to move when pry bar pressure is released indicates that the driven equipment assembly must be moved rearward on the base assembly or, if
used, the number of shims between the input flange and the flexible coupling must be reduced.
Tolerances and Torque Values
Permissible alignment tolerances and torque values for Caterpillar standard mounting hardware are available from your Caterpillar.
CAUTION: DURING OPERATION, SHOULD A CHANGE IN THE VIBRATION
OR SOUND LEVEL OCCUR, ALIGNMENT SHOULD BE RECONFIRMED. THIS IS PARTICULARLY TRUE FOR SEMIMOBILE INSTALLATIONS AND ON ANY FIXED INSTALLATIONS WHICH ARE SUBJECT TO INFREQUENT RELOCATION. ALIGNMENT SHOULD ALSO BE CHECKED ON A PERIODIC BASIS OR AT TIME OF MOVEMENT IF INSTAL- LATION IS ON A SUBBASE OR SKID- TYPE BASE.
