Cummins/Onan — Continuity tests may be performed

For these Cummins/Onan models: 4MCCK, 605MCCK.

Applies to: Cummins Onan 4Mcck, Cummins Onan 605Mcck

Procedure

1. 1. The first step is to remove generator band and end bell cover. Remove all brush springs and lift the brushes from their holders.
2. 2. Remove generator through-stud-nuts. Hold both the end bell and frame assembly, since they are separate parts, and remove them as One assembly from the adapter. Screwdriver slots in the adapter provide for prying the frame loose. Be careful not to let the frame assembly rest or drag on the armature.
3. 3. Remove baffle ring from adapter. Turn armature through-stud nut out to the end of the through stud. While pulling the armature outward with one hand, strike a sharp endwise blow on the nut with a heavy soft-faced hammer to loosen the armature. If the armature does not come loose, strike the armature with a sharp downward blow in the center of the lamination .stack with a lead or plastic hammer. Rotate the armature and repeat. Be careful not to hit the collector rings, commutator, bearing or windings.
4. 4. Upon disassembly, all parts should be wiped clean and visually inspected. BRUSHES AND SPRINGS Inspect brushes periodically. Replace if worn to 5/8". Replace springs. if damaged or if proper tension is ques­ tionable. Rapid brush wear may be caused from high mica between commutator bars, rough commutator or col­ lector rings, or from a deviation from neutral position in the adjustment of the brush rig. Never bend the constant­ See INSTALL BRUSHES WITH BEVELLED TOP SLANTING DOWN . TOWARD SPRING HOLDER TO REMOVE BRUSH SPRING HOLDER DOWN AND OUT AS SHOWN IN BROKEN LINES. The brush rig must be aligned in the neutral position. If it is not, sparking occurs. Normally, the neutral position If the mark is lost or a new brush rig installed, follow· these instructions to find the neutral position:
5. 1. With the generator end cover and band removed to allow access to the rig, connect a voltmeter across the DC terminals and start the unit and apply full rated load.
6. 2. Loosen the brush rig mounting screws and rotate the rig to get the highest voltage.
7. 3. Rotate the rig in one direction until the voltmeter reading starts to decrease. Mark this point.
8. 4. Repeat Step 3 in the other direction.
9. 5. Half the distance between the two marked points. is the neutral position. above procedure, but mark the point where arcing begins. 29 An HACK SAW BLADLl '-MICA PROp·ERLY UNDERCUT ~L~DE ) • ••• • ·0 I' ... ~ICA...Ji RIGHT WAY . \ Q TO GRIND TEETH ~, WRONG TO TEETH GRIND BLADE WIDTH OF MICA COMMUTATOR BARS WORN BELOW LEVEL OF MICA SEPARATORS CAUSE SPARKING. JUMPING. NOISY BRUSHES LOCATION OF REFERENCE MARK ~BRUSH RIG COLLECTOR RINGS If the collector rings become grooved or out-of-round, or the brush surface becomes pitted or rough so that good brush seating cannot be maintained, remove the armature and refinish the collector rings in a lathe. If the com­ mutator appears to be rough or scored, refinish it at the same time. Remove or adequately shield the ball bearing during refinishing. COMMUTATOR Commutator bars wear with usage so that the mica between them must be undercut. This should be done as Soon as the mica on any part of the commutator touches the brushes. blade. Avoid injury to the surfaces of the copper bars. Leave no burrs along the edges of the bars. Undercut GENERATOR TESTING Windings: Before making any tests, lift all b rushes from their holders and disconnect the load circuit wires from the plant. If the armature tests defective, the practical repair is to replace. it. If a field coil tests defective, replace the entire coil assembly unless the trouble is in one of the external leads. Then it can be repaired as the nature of the trouble requires. Armature Ground: Lift or remove brushes so that none contact the commutator or collector rings. Use a continuity Place one. test prod on the commutator, and the other test prod on a clean part of the armature shaft. The test prods must make good electrical contact. The test lamp should not glow. If the test lamp glows, the DC winding or the commutator is grounded. To test AC windings, place one test prod on one of the collector rings arid the other test prod on the armature shaft. If the test lamp glows, AC windings or a collector ring is grounded. Replace grounded armatures. Armature Open: Armature AC windings may be tested for an open circuit without removing the armature. Testing the DC winding requires removal and the use of an armature To test AC windings, lift or remove all brushes. Use a test lamp set. Place one test prod on each of the collector rings. If the lamp does not glow, AC windings are open circuited. To test the DC windings, place the armature in a growler. Then pass a smooth steel strip across the commutator segments. Repeat all around the commutator. At some pOint around the commutator, a spark should occur as the strip contacts two adjacent segments. Rotate the armature slightly and repeat the test. Continue until a spark is WAY GRIND TO 30 obtained between all adjacent segments. If no spark is obtained at some point, an open circuit i~ indicated. IMPORT ANT: A short circuit in the win<~ng might prevent sparking. This condition may also b€ indicated by the short circuit test. Replace an open circuited armature with a new one. Armature Short: To test for a short circuit, place the armature in a growler- and hold a steel strip about 1/2" above the armature laminations. Pass the strip back and forth over the laminations. Cover as much of the lamination area as possible. If the strip is magnetically attracted to the armature at any point, a short circuit is indicated. After testing in one position, rotate the armature slightly in the growler and repeat the test. Continue until a complete armature revolution in the growler has been made. Replace a short circuited armature with a new one. Field Windings: Use a test lamp set for all tests except a short circuit. The field coils are saturated shunt wound, having a series field winding for cranking. When testing a field coil assembly, disconnect all of its external leads from their terminals. Tag and mark each lead to assure proper connections for assembling. Testing Field Windings {or Grounds: To test a coil as­ sembly fO!: ground, disconnect its external leads and touch one test prod to the terminal of one of its leads and the other test prod to the generator frame. If the lamp lights, the coil assembly being tested is grounded. The ground may be in a coil, coil connection, Or coil lead. Repair or replace as needed. Testing Field Windings for Open Circuit: To test a coil assembly for an open circuit, disconnect its external leads and touch one test prod to the terminal of one coil winding lead, and the other test prod to the other lead (or leads) of that coil winding. If the lamp does not light, the winding being tested is open. If the fault lies in a connection between coils, or in a coil lead, the connection can be repaired. If it is inside the coil, replace the entire coil assembly with a new one. Boll Bearing: If the armature ball bearing needs replace­ true to serve as a turning center when refinishing the commutator or collector rings. Drive the bearing onto the shaft shoulder. Use a double-sealed prelubricated ball bearing. Shunt Field Rectifier: Using a multimeter, check the rectifier for an open circuit in one direction and a closed circuit in the other direction. If the rectifier is defective in either direction, replace it. Assembly:
10. 1. Clean and inspect all mating surfaces. Surfaces should be free of nicks and dirt.
11. 2. Coat mating area between the generator shaft and the engine crankshaft with a thin film of lubricating oil, Molycoat or equal.
12. 3. Assemble the armature through stud to the engine
13. 4. Check to see that the key is in the crankshaft. TEST LAMP - FOR TESTING FOR A654 OPEN CIRCUITS AND GROUNDS - USE 3 OR 4 CANDLEPOWER BULB COMMUTATOR 31
14. 5. Slide armature over the through stud and onto the crankshaft, being careful not to let the weight of the . armature rest ori the through stud.
15. 6. Install baffle ring, when used.
16. 7. Assemble generator through studs to' the adapter ~ DO NOT tighten the armature or rotor ~ through stud before mounting the frame and bearing support. If this procedure is not followed, mai.n and outboard. bearings. quirements could be. doubled, resulting in damage to the commutator and DC brushes.
17. 8. Install the frame and bearing support. Tighten frame
18. 9. NOW Because you have tightened the frame and bearing support before tightening the armature, you have the
19. 10. Tap the bearing support in the horizontal and vertical plane with a lead hammer to relieve stresses on the 32 CONTROL SYSTEM All relays are shown in the de-energized position. If any control part fails, replace the defective part with a part of identical manufacture. No attempt should be made to repair such parts as meters, fuses, switches; relays, or receptacles. Check all electrical connections and contacts whenever servicing control equipment. .~ Always disconnect the battery to avoid ~ accidentally starting the plant • When disassembling controls, tag each lead that has to be removed and mark the connection point of the lead (on the tag) to assure correct connections for assembly. The plant control system regulates starting, stopping, battery charging and provides a means of emergency automatic stopping. Control system defects can best be analyzed with the proper wiring diagram •. When using Onan wiring diagrams, remember these points. The views shown are modified pictorially. Components are shown in their actual positions. Normally, the top view of each component is shown for terminal location. Dotted lines show the edges of the control box and indicate . the direction from which it is being viewed, i.e. Top View. series Automatic Control manual number 907.8. ~\. GENERAL DESCRIPTION The Control-O-Matic, standard on newer niodel MCCK plants, is an engine-control, an automatic-demand control and a bilge-blower control,all combined into one top­ mounted control box. The Control-O-Matic, with its switch in AUTOMATIC position, will monitor the AC load circuit to: a. Sense a load on the AC line. b.. Close the bilge blower circuit (when used). c. Open the bilge blower circuit. d. Start the electric plant. e. Sense when all load is removed. f. Stop the electric plant. A sheet metal enclosure approximately 12-5/8// wide,
20. 7. 5/8" deep, and 6" high houses the Control-O-Matic. The Control-o-Matic mounts on top of the electric plant with its front panel facing the generator end of the plant. The front panel holds the charge ammeter, emergency relay, and toggle switch. A unique hinge arrangement holds the front panel, cover and chassis together. The control box may be opened in a very limited space to expose all the relays for servicing. HOW CONTROL-O-MATIC WORKS A three position toggle switch on the front panel selects (\ one of three modes of operation; RUN; OFF; and AUTO­ MATIC. The Bilge-Blower Control circuit in the Control-O-Matic CONTROL-O-MATIC delays cranking while it closes a 12-volt, 5-amp circuit. to operate the bilge blower. When the three position toggle switch is moved to the RUN position, the Bilge-Blower Control goes thro~gh its control cycle before the electric plant cranks and runs. The electric plant stops when the three-position switch is moved to the OFF position. If the operator places the three-position switch in the AUTOMATIC position, the electric plant will crank and run on load demand after the Bilge-Blower Control cycles. The electric plant stops when all the load is removed . from the AC line. OPERATION OF CONTROL·O-MATIC Control-a-Matic operation is· explained on the following pages. Accompanying the description of each function is a schematic drawing, with 'Current flow shown as bold lines on the draWing. A pietorial wiring diagram apPears Throughout the text are references to various components (electrical devices), terminal positions, and current flow. When reading through' the text, follow current flow on the schematics and locate . relative positions of electrical devices and terminal hensive understanding of the operation of the Control-o­ Matic. 33 613C I M f5\ It>! rMt LOt> t-------------------------+­ I I I ~__ -----~~-----~-, II r--~- "::dIaI ~

Source: manual:927-0550 Onan MCCK (spec A-C) Marine Genset Service manual (04-1969).pdf. Figures and steps are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.