Page 59 - Mechanic Diesel - TT
P. 59
MECHANIC DIESEL - CITS
Carbon build-up is another problem encountered with heads. The carbon tends to hold heat which ignites the
fuel prematurely. When pre-ignition is experienced in the engine and it cannot be remedied through the electrical
system, the head is usually at fault.
Cylinder Head Troubleshooting and Remedies: If the two adjacent cylinders are misfiring, perform a
compression test to verify the problem before removing the cylinder head (it could be faulty ignition). When a head
gasket “blows,” the break is usually between two adjacent cylinders, and air, instead of being compressed, simply
moves back and forth between the cylinders (fig 3-9). A compression test would indicate little or no compression
in either of these two cylinders to remedy this problem, the head gasket must be replaced. The cylinder head and
block must be checked to ensure the surface has not warped. A perfectly flat surface is required to ensure an air-
tight seal. If an uneven surface is detected on either the cylinder head or the cylinder block, it must be machined
flat (commonly termed shaving or grinding the head or block).
If pre - ignition exists, and after troubleshooting electrical system, it is determined that the cylinder head is the
cause, remedy the malfunction by removing the head and cleaning out all carbon deposits.
Valve Troubleshooting and Remedies: Let’s return to the compression test for a moment. If a dry” test and a
“wet” test result in the same low reading, this indicates an “open” combustion chamber (a blown head gasket, a
cracked piston head, a valve adjusted too tightly, etc.). A visual inspection would eliminate the head gasket and
you can eliminate a cracked piston if there is no sound to indicate it. You will probably have to remove the cylinder
head, but first, let’s adjust the valves to ensure that they are not too tight. Adjust the valves by inserting a feeler
gage between the rocker arm and the valve stem and turning the adjusting nut until a slight drag is felt (fig 3-12).
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CITS : Automotive - Mechanic Diesel - Lesson 11 - 14
