Cummins/Onan — Procedure (4 steps)

For these Cummins/Onan models: GNH, GV12.

Applies to: Cummins Onan Gv12

Procedure

1. 2. Low power.
2. 3. Abnormal water or oil temperature.
3. 4. Unusual engine noises.
4. 5. Excessive smoke. Damper hub and inertia member are stamped with an index mark to permit detection of movement between the two hub and inertia member resulting from engine operation. N11931 Clean Electric Units And Tighten Connections Dust and dirt, if allowed to accumulate in the generator/ alternator and cranking motor, will cause excessive wear of bearings, brushes and commutator. Remove the cover band.and blow out dust and dirt with Tighten Electric Connections Hard starting is often traceable to loose or corroded bat- tery connections. A loose connection will overwork the bat- tery-charging generator/alternator and regulator and short- en their lives. Add distilled water to battery cells to keep tops of plates covered. Remove corrosion from and around terminals; then coat with petroleum jelly. Keep connections clean and tight. Prevent wire and lugs from touching each other or any metal except screw ter- minals to which they are attached. Replace broken or worn wires and their terminals. Have battery tested periodically. Follow battery manufac- turer's instructions for maintenance. Check Battery-Charging Generator/Alternator Brushes And Commutator (D Check) The failure of a generator/alternator may cause unit down- time and nearly always results in expensive replacement. Clean dirty commutators with No. 00 sandpaper; never use emery cloth. check for incorrect brush spring tension or high mica on the commutator. Check output and action on an ammeter indi- cator after brush replacement. Shorts and incorrect generator polarization can be detected at the ammeter. lncorrect polirization is indicated by " minus reading when generator is in operation. Take unit to an electric service station for immediate correction. Clean Engine (D Check) Dirt from the outside will find its way into the lubricating oil filter cases and into the rocker housings when the covers are removed unless dirt is removed first. 1 . 1 . Servrce Manual Cummins Gas Engines Maintenance d-21 Check Crankshaft End Clearance (E Gheck) The crankshaft of a new or newly rebuilt engine must have engine must not be operated with more than the worn limit Engine Series New Min. New Mar. Worn Limit G N H GVl2
5. 0. 007"
6. 0. 006"
7. 0. 015"
8. 0. 013"
9. 0. 035"
10. 0. 035"
11. 3. 22 Cummins Gas Engines Maintenance Service Manual by mechanics thoroughly familiar with worn replacement limits and with disassembly and assembly procedures. This information is avaliable in all Cummins Shop Manuals which can be purchased from any Cummins Distributor. Inspect the following items at this period: Main and Connecting Rod Bearing Shells Crankshaft Journals Camshaft Lobes Cylinder Heads (Grind Valves) Cylinder Liners Pistons and Rings Carburetor Gas Shut Off Valve Oil Cooler (Clean) "Mag-tronic" lgnition and Spark Plugs Battery-charging .Alternator/Generator and Cranking Motor lntake and Exhaust System (Clean and Correct Leaks) Parts which are worn beyond replacement limits at this in- spection should be replaced with new or rebuilt parts or u n its. Engine Rebuild lf, during the major inspection, it is determined that crank- shaft journals or any other engine parts are worn beyond worn replacement limits, the engine should be removed and completely rebuilt. After an engine has been rebuilt it is essentially a new en- gine and should be treated as such. By treating the rebuilt engine like a new engine and by following the preventive maintenance schedule, the same dependable service can be expected from the engine that it gave during its first service period. __ Service Manual Cummins Gas Engines Removal, Installation and Adjustment For all unit rebuilding or parts installation, see the nearest Cummins Distributor who is equipped to rebuild all Cum- mins engines or engine units. Through the use of the Shop chanics, a rebuilt engine will perform as well as a new one.
12. 4. 1 Standard and Optional Component Servicing Remov?l, Installation and Adjustment The design of Cummins Gas Engines makes it possible to replace worn units with new or rebuilt units in a short time so the engine may be placed back in service with a mini- mum of downtime. Use only Cummins parts in Cummins Gas Engines. Years have been spent developing and testing these parts - each in relation to its mating part. Cummins Gas Engines deserve only the finest replacement parts - genuine Cummins Parts. Protect all machined surfaces from contact with corners, edges, rough surfaces, dust, dirt or any material that will mar, scratch or damage these surfaces in any way. Protect all parts which are to be stored with an oil or grease film. Always provide a clean place to work and clean outside of the engine before removing any units. Clean Engine Exterior After removal of electrical equipment, but before removal of other components, steam clean engine thoroughly. Refer to Engine Wiring Diagram, Section 5, In addition to actual time saved by engine cleaning, the quality of work will be improved. satisfactory for general use on Cummins Engines. This type cleaner can be used in either cleaning room or yard. Spark Plugs Removal 1, Remove ignition harness wire from transformer terminal.
13. 2. Remove screws securing transformer cover, retainer, spring and transformer ground wire to rocker cover; lift off cover. Fis. 4-1. the transformer assembly is spring loaded to assure contact with spark plug. Lift transformer, spring, spring retainer and cover assembly from the spark plug adapter tube. remove spark plug from adapter. Lift out spark plug and gasket. Installation Check spark plug gap; it should be 0.018 inch. Inspect spark plug seating area of the adapter and clean to insure a good seating surface for the spark plug. Position new gasket on spark plug; insert spark plug in 1 .
14. 4. 2 be used under the transformer to installed, a spacer must prevent excessive pres- n IJ tu ^wMw% \ NGlO lnsert transformer spring and spring retainer into spark plug adapter tube; place transformer cover over spring retainer, secure cover, spring retainer and transformer ground wire to rocker cover with screws. the proper engine cylinders. Connect the ignition harness lead to the transformer ter- minal. Mag-Tronic lgnition
15. 1. Crank engine in direction of rotation until rotor arm is cen- tered in timing window of "Mag-tronic" distributor head, cylinder for GNH Series and No. 1-R for GV12 Series.
16. 2. Disconnect wiring harness from "Mag-tronic".
17. 3. Remove nuts, capscrews, flatwashers and lockwashers se- tronic" from drive assembly. lnstallation
18. 1. Rotate "Mag-tronic" drive until rotor arm is centered in timing window.
19. 2. Position "Mag-tronic" to drive assembly, engaging drive Service Manual Cummins Gas Engines Removal, Installation and Adjustment flatwashers and nuts. (Do not tighten capscrews.) N G1 2
20. 3. Plug wiring harness into "Mag-tronic".

Source: manual:960-0010 Cummins GNH series Nat Gas Engine Service Manual (1-1966).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.