ALIGNMENT 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 engine and 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 26. 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. Any change 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 machin- ing 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 27.)

Checking Outside Diameter Run Out While turning the hub through 360° of rota- tion, 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 dri- ven sides of the coupling have been found within limits, the engine and load align- ment can be checked. There are two kinds of misalignment: parallel and angular (bore and face). (See Figures 28.)

Figure 28

Figure 29

Checking Parallel Alignment

Parallel misalignment can be detected by attaching a dial indicator, as shown in Figure 29, 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 bear- ing 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 align- ment 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 30.

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 exces- sive base deflection under torque reaction load. This has the effect of introducing a side to side centerline offset which disap- pears 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 sup- ported 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 pul- leys 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 dri- ven 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 tor- sional 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 dif- ferent speeds.

As a general rule, the angle should be the same on each end of the shaft. (See Figure 31.) 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