Cummins ISL-G Valve Adjustment

BusTekHub Cummins ISL-G Valve Adjustment



⇒Engine: Cummins ISL-G
⇒Displacement: 8.9
⇒Fuel: CNG / LNG
⇒Rating: 280Hp /320Hp
⇒Valve Lash Cold:
⇒Intake Valves .014 in. (0.356 mm)
⇒Exhaust Valves .030 in. (0.762 mm)
⇒Valve locknut 212 in. lbs.
⇒Valve Cover 212 in. lbs.
⇒Coil Brackets 80 in. lbs.
Note: 12 in. lbs. = 1 ft. lb.
⇒ Valve Adjustment Intervals: initial adjustment at 1,000 hours, then every 2,000 hours. Mileage intervals vary depending on vehicle average speed.


Parts are subject to change, depending on wear. Seals and O-rings should be replaced to avoid oil leaks. Hard parts should be replaced if damaged or missing.


Cummins ISL-G Valve Cover Part Numbers
Cummins ISL-G Valve Cover Part #
Cummins ISL-G Crankcase Breather Part Numbers
Crankcase Breather Part #


2 – 12mm X 1.75 Bolts
Pry bar
5mm Allen socket
Schley Products 14mm valve adjustment tool #____________ or 14mm wrench
General wrench set for valve cover removal
.014 feeler gauge (intake valves)
.030 feeler gauge (exhaust valves)
Torque wrench
Cummins Barring Tool  #3824591
Note: This tool is optional, engine can be barred form crankshaft pulley. 

Cummins ISL-G Valve Adjustment Tools
Valve Adjustment Tools
Cummins Engine Barring Tool
Cummins Engine Barring Tool



⇒Prior to working on vehicle, turn off batteries or disconnect battery ground.
⇒Wear proper protective equipment.
⇒Follow manufacture’s recommended service and safety procedures.
⇒This instructional article is a supplement to the manufacture’s service procedures.


Tech Info:

Valve adjustments are a critical part of the preventive maintenance and the bus repair process. When performing a valve adjustments, several things have to be kept in mind:

⇒Engine should be at 140⁰ F or less.
When engine comes in for a performance complaint related to valve adjustment:
Check valve height – valve may recess into head causing performance complaints
Check the rocker shafts for wear – this may cause the rocker to bind



1. Remove Turbo Actuator Air Line
2. Remove EGR Cooler crossover tube
3. Remove Crankcase Breather
4. Remove Coolant Line
5. Disconnect ignition harness from ignition coils
6. Remove ignition coils with brackets. Remove the coils by pulling assembly straight up. Do not wiggle back and forth, this will cause damage to components.

Cummins ISL-G Valve Adjustment
Valve Adjustment Component Removal

 7. Remove valve cover bolts.

Cummins ISL-G Valve Adjustment
Valve Cover Bolts

8. Remove valve cover.

Cummins ISL-G VAlve Adjustment
Valve Cover Removal

 9. The recommended practice is to use the valve overlap method. This is the fastest way to adjust the valves and also very accurate. There are two ways to rotate or bar the engine over.

a. The OEM recommended way of rotating the crankshaft is by turning at the flywheel. This is done with Cummins tool #3824591. On transit buses, however, this is hard to do in most cases. An alternate method is to rotate the engine through the front crank pulley.

Cummins Engine Barring Tool
Cummins Engine Barring Tool

b. To Rotate the engine using the front crank pulley, install two 12mm x 1.75 bolts into crank pulley. Use a pry bar to rotate engine.

Cummins ISL-G Valve Adjustment
Cummins Crank Pulley Turning

 10. Rotate engine until valve overlap is reached on cylinder #6. Valve overlap is reached when both the intake and exhaust valves on the cylinder are opened at the same time. You will notice that as the exhaust valve is closing the intake valve starts to open. When both valves are in motion, they are in overlap. Valve overlap occurs for about 15° of crankshaft rotation. As the intake valve starts to close the exhaust valve starts to open.

Cummins ISL-G Valve Overlap
Cummins Valve Overlap

 11. Once valve overlap is reached on cylinder #6; cylinder #1 will be at Top Dead Center (TDC). You can verify this by moving both intake and exhaust rockers on cylinder #1 and ensuring they are loose indicating both valves are closed. Make a reference mark on the crank pulley and gear train housing cover.

Cummins ISL-G Timing Mark
Cummins Timing Mark

12. Valves to adjust on valve overlap on cylinder #6.
Adjustment Specification cold (below 140º F):
Intake: .014 in. (0.356 mm)
Exhaust: .030 in. (0.762mm)
You can now proceed and adjust the valves:

Cummins ISL-G Valve Overlap Cyl. 6
Valve Overlap Cyl. 6

During the adjustment, keep in mind to:

⇒Keep medium drag on the feeler gauge to complete adjustment.
Tight valves will cause performance issues. 
Loose valves will cause noise and performance issues.
Recheck lash after tightening adjuster screw.

Cummins ISL-G Valve Adjustment
Adjusting Valves

 13. After adjusting valves on valve overlap on cylinder #6, rotate the engine a full revolution 360°. Align the previously made reference marks. Cylinder #1 is now in overlap and cylinder #6 at Top Dead Center (TDC).

Cummins ISL-G Barring Engine
Barring Engine Over

14. Valves to adjust on valve overlap on cylinder #1.
Adjustment Specification cold (below 140º F):
Intake: .014 in. (0.356 mm)
Exhaust: .030 in. (0.762mm)
You can now proceed and adjust the valves:

Cummins ISL-G Valve Overlap
Valve Adjust Cyl 1 Valve Overlap

⇒Ensure that the adjustment has held by rotating engine through 2 full rotations and check that the valve lash is still at specification.


15. Install valve cover gasket; the gasket is a split-type design. Ensure it seats correctly in the groove all around the valve cover.

Cummins ISL-G Valve Cover Seal
Valve Cover Seal

16. Install valve cover, but before doing so, clean sealing surface on cylinder head. Install new o-rings on valve cover bolts. Install valve cover bolts and tighten from the center bolt,  working outward in a spiral pattern to avoid distorting valve cover. Torque valve cover to 212 in. lbs.

Cummins ISL-G Valve Cover O-rings
Install Valve Cover O-rings


Cummins ISL-G Valve Cover
Install Valve Cover Bolts


Cummins ISL-G Valve Adjustment
Tighten Valve Cover Bolts

17. Install new O-ring on crankcase breather and install unit. And connect hoses to unit.
Note: Use caution when installing crankcase breather not to damage or twist O-ring. If O-ring is damaged, it will result in an oil leak that can be confused as a engine rear main seal leak. The oil will leak down the bell housing.

Cummins ISL-G Crankcase Breather
Crankcase Breather

18. Install EGR cooler crossover tube, use new gaskets to prevents leaks.
19. Install turbo actuator line, and insure you have a leak free connection.
20. Install coolant line (this may not apply to all models).
21. Install ignition coils with brackets. Note: This can be a good time to install new spark plugs, since coils are removed.
22. Re-connect ignition coils.

Cummins ISL-G Valve Cover Components
Re-connect Components

23. Verify all connections, and start engine. Bring engine to operating temperature and check for leaks.
24. Road test to check for proper engine operation.

















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