Hummer H2. Manual - part 1697

LOWER ENGINE NOISE, REGARDLESS OF ENGINE SPEED 

Lower Engine Noise, Regardless of Engine Speed 

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The engine block oil galleries  

Broken valve spring

Replace the valve spring and spring shim.

Worn or dirty valve lifters

Replace the valve lifters.

Stretched or broken timing chain 
and/or damaged sprocket teeth

Replace the timing chain and sprockets.

Worn engine camshaft lobes

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Inspect the engine camshaft lobes.  

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Replace the camshaft and valve lifters as required.  

Worn valve guides or valve stems

Inspect the following components and repair as required: 

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The valves  

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The valve guides  

Stuck valves 
Carbon on the valve stem or valve seat 
may cause the valve to stay open.

Inspect the following components and repair as required: 

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The valves  

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The valve guides  

Cause

Correction

IMPORTANT:

A cold piston knock which disappears in 1.5 minutes should be considered acceptable. A cold 
engine knock usually disappears when the specific cylinder's secondary ignition circuit is grounded 
out during diagnosis. 
A low rumble/knocking may indicate a crankshaft or piston, lower engine, concern.

Low oil pressure

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Perform an oil pressure test. Refer to Oil 
Pressure Diagnosis and Testing .  

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Repair or replace damaged components as 
required.  

Worn accessory drive components 
Abnormalities such as severe cracking, bumps or 
missing areas in the accessory drive belt and/or 
misalignment of system components.

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Inspect the accessory drive system.  

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Repair or replace as required.  

Loose or damaged crankshaft balancer

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Inspect the crankshaft balancer.  

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Repair or replace as required.  

Detonation or spark knock

Verify the correct operation of the ignition controls 
system. Refer to Detonation/Spark Knock in 
Engine Controls - 6.0L.

Loose torque converter bolts

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Inspect the torque converter bolts and 
flywheel.  

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Repair or replace as required.  

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

  

ENGINE NOISE UNDER LOAD 

Engine Noise Under Load 

Loose or damaged flywheel

Repair or replace the flywheel.

Oil pump screen loose, damaged or restricted

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Inspect the oil pump screen.  

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Repair or replace as required.  

Excessive piston-to-cylinder bore clearance

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Inspect the piston and cylinder bore.  

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Repair as required.  

Excessive piston pin-to-bore clearance

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Inspect the piston, pin, and connecting rod.  

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Replace the piston, pin and connecting rod 
as an assembly, as required.  

Excessive connecting rod bearing clearance

Inspect the following components, and repair as 
required: 

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The connecting rod bearings  

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The connecting rods  

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The crankshaft  

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The crankshaft journals  

Excessive crankshaft bearing clearance

Inspect the following components, and repair as 
required: 

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The crankshaft bearings  

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The crankshaft journals  

Incorrect piston, piston pin and connecting rod 
installation 
Pistons must be installed with the mark or dimple on 
the top of the piston facing the front of the engine. 
Piston pins must be centered in the connecting rod 
pin bore.

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Verify the pistons, piston pins and 
connecting rods are installed correctly. Refer 
to Piston, Connecting Rod, and Bearing 
Installation .  

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Repair as required.  

Cause

Correction

Low oil pressure

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Perform an oil pressure test. Refer to Oil Pressure Diagnosis and 
Testing .  

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Repair or replace as required.  

Detonation or spark knock

Verify the correct operation of the ignition controls. Refer to 
Detonation/Spark Knock in Engine Controls - 6.0L.

Loose torque converter bolts

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Inspect the torque converter bolts and flywheel.  

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Repair as required.  

Cracked flywheel - automatic 
transmission

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Inspect the flywheel bolts and flywheel.  

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Repair as required.  

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

  

ENGINE WILL NOT CRANK - CRANKSHAFT WILL NOT ROTATE 

Engine Will Not Crank - Crankshaft Will Not Rotate 

Excessive connecting rod 
bearing clearance

Inspect the following components, and repair as required: 

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The connecting rod bearings  

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The connecting rods  

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The crankshaft  

Excessive crankshaft bearing 
clearance

Inspect the following components, and repair as required: 

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The crankshaft bearings  

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The crankshaft journals  

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The cylinder block crankshaft bearing bore  

Cause

Correction

Seized accessory drive 
system component

1. Remove the accessory drive belts.  

2. Confirm that the engine will rotate. Rotate the crankshaft by hand 

at the crankshaft balancer or flywheel location.  

3. Repair or replace the components as required.  

Seized automatic 
transmission torque converter

1. Remove the torque converter-to-flywheel bolts.  

2. Confirm that the engine will rotate. Rotate the crankshaft by hand 

at the crankshaft balancer or flywheel location.  

3. Repair or replace the components as required.  

Broken timing chain

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Inspect the timing chain and gears.  

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Repair or replace the components as required.  

Seized timing chain or timing 
gears

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Inspect the timing chain and gears for foreign material or a seized 
chain.  

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Repair or replace the components as required.  

Seized or broken camshaft

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Inspect the camshaft and the camshaft bearings.  

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Repair or replace the components as required.  

Bent valve in the cylinder 
head

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Inspect the valves and the cylinder heads.  

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Repair or replace the components as required.  

Seized oil pump

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Inspect the oil pump assembly.  

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Repair or replace as required.  

Hydraulically locked cylinder 

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Coolant/antifreeze in 
the cylinder  

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Oil in the cylinder  

1. Remove spark plugs and check for fluid in the cylinder. When 

rotating the engine with the spark plugs removed, the piston, on 
compression stroke, will push fluid from the combustion chamber. 
Refer to Coolant in Combustion Chamber .  

2. Inspect for failed/broken head gaskets.  

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2

  

COOLANT IN COMBUSTION CHAMBER 

Coolant in Combustion Chamber 

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Fuel in the cylinder  

3. Inspect for a cracked engine block or cylinder head.  

4. Inspect for a sticking fuel injector.  

5. Repair or replace the components as required.  

Material in the cylinder 

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Broken valve  

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Broken piston rings  

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Piston material  

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Foreign material  

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Inspect the cylinder for damaged components and/or foreign 
materials.  

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Repair or replace the components as required.  

Seized crankshaft or 
connecting rod bearings

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Inspect crankshaft and connecting rod bearings.  

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Repair or replace the components as required.  

Bent or broken connecting 
rod

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Inspect the connecting rods.  

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Replace the piston, pin and connecting rod as an assembly, as 
required.  

Broken crankshaft

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Inspect the crankshaft.  

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Repair or replace the components as required.  

Cause

Correction

DEFINITION: Excessive white smoke and/or coolant type odor coming from the exhaust pipe may 
indicate coolant in the combustion chamber. Low coolant levels, an inoperative cooling fan, or a faulty 
thermostat may lead to an "overtemperature" condition which may cause engine component damage. 

1. A slower than normal cranking speed may indicate coolant entering the combustion chamber. 

Refer to Engine Will Not Crank - Crankshaft Will Not Rotate .  

2. Remove the spark plugs and inspect for spark plugs saturated by coolant or coolant in the cylinder 

bore.  

3. Inspect by performing a cylinder leak-down test. During this test, excessive air bubbles within the 

coolant may indicate a faulty gasket or damaged component.  

4. Inspect by performing a cylinder compression test. Two cylinders "side-by-side" on the engine 

block, with low compression, may indicate a failed cylinder head gasket. Refer to Engine 
Compression Test .  

Cracked intake 
manifold or failed 
gasket

Replace the components as required.

Faulty cylinder head 
gasket

Replace the head gasket and components as required. Refer to Cylinder Head 
Cleaning and Inspection and Cylinder Head Replacement - Left or Cylinder 
Head Replacement - Right .

Warped cylinder 

Machine the cylinder head to the proper flatness, if applicable and replace the 

 

2004 Hummer H2 

2004 ENGINE Engine Mechanical - 4.8L, 5.3L, and 6.0L - Hummer H2