GEI 56128-L
© Copyright 2016 General Electric Company
7
3.
For base assembly and motor mounting, the mounting bolts must be tightened to prevent changes in
alignment and possible damage to the equipment. It is recommended that a washer be used under each
nut or bolt head to get a secure hold on the motor feet. As an alternative, flanged nuts or bolts may be
used. The recommended tightening torques for medium carbon steel mounting bolts, SAE Grade 5, are
listed below in Table 1. For recommended tightening torques of other hardware on the motor see tables
4A, and 4B in the Tightening Torque section of this book.
Table 1
Bolt Size
Recommended Torque
in Ft-Lb (N-M)
Inch
Metric
Minimum
Maximum
1/4
(M6)
7
(9)
11
(15)
5/16
(M8)
14
(19)
21
(28)
3/8
(M10)
25
(34)
37
(50)
1/2
(M12)
60
(81)
90 (122)
5/8
(M16) 120 (163) 180 (244)
3/4
(M20) 210 (285) 320 (433)
Note:
For low carbon steel bolts, use 50% of the above recommended tightening torques. There are no ID marks on
low carbon steel bolts.
4.
For direct coupled applications use flexible couplings if possible.
Accurate mechanical lineup is essential for successful operation. Mechanical vibration and roughness in
running the motor may be an indication of poor alignment. In general, lineup by straight edge across,
and feeler gauges between coupling halves is not sufficiently accurate. It is recommended that the
lineup be checked with a dial indictor and checking bars connected to the motor and load-machine
shafts. The space between coupling hubs should be maintained as recommended by the coupling
manufacturer. Shaft offset should not exceed 0.002”. Angular misalignment should be less than 0.002”.
5.
The application of pulleys, sheaves, sprockets, and gears on the motor’s shaft is shown in NEMA Standard
MG1-14.07. The application of the V-belts dimensions for alternating current motors is in MG1-14.42. V-
belt sheave pitch diameters should not be less than the values shown in Table 14-1 of NEMA MG-1.
Sheave ratios greater than 5:1 and center-to-center distances less than the diameter of the large sheave
should be referred to the Company. Make certain that the minimum allowed diameter of the motor
pulley and the maximum belt tension are not exceed because an excessive pull may cause bearing
trouble and shaft failures. Tighten belts only enough to prevent slippage. Belt speeds should not exceed
5000 feet per minute (25 meters per second). When V-belts are used, sheave ratios greater than 5:1 and
center-to-center distances less than the large sheave shall not be used. The dimensions of the belt pulley
are to be determined according to the kind of belt, transmission and capacity to be transmitted. Vent
holes have to be kept free and required minimum distances are to be observed in order not to obstruct
the flow of cooling air. In addition, make sure that the discharged hot air is not re-circulated into the
motor.
C.
Sleeve Bearing Endplay
On sleeve-bearing motors, the feet should be located at a correct distance from the load so that the motor’s
rotor is in the approximate mid-point of its endplay. The mid-position of the rotor’s endplay is indicated with a mark
on the motor’s shaft. Locate this mark flush with the bearing housing.
D.
Power Supply and Connections
1.
Nameplate voltage and frequency should agree with the power supply. Motors will operate satisfactorily
on line voltage within ±10% of the nameplate value or frequency within ±5%, combined variation not to
exceed ±10%.
