After studying this exercise, students will be able to understand:
i. the inspection methods of various parts of I.C. engines,
ii. the repair procedure of various parts of I.C. engines.
Preventive maintenance ensures that an internal
combustion (I.C.) engine will operate efficiently. By
following the schedule, engine casualties are reduced
and engine achieves its normal number of operating
hours between overhaul periods. While performing
an engine maintenance or overhaul, some precautions
have to be taken such as: planning the work, before
beginning a repair keep necessary tools/parts ready,
keeping the necessary forms ready to record the
clearances, dimensions, and measurements and
checking precision measuring instruments before
using them. Apart from this keeping the work area
clean, not allowing oil to accumulate on the deck or
on the tools, Before starting to inspect/repair, clean
the outside of the engine thoroughly. This will help
you spot cracks, leaks, and other problems more
easily than if the engine is dirty.
Engine block is made of grey cast iron. It is single piece casting consisting of cylinders, water jacket,
passageways, openings for inlet and outlet valves etc.
Engine block inspections:
Inspect the top surface of the cylinder block for damage (warpage). You can use a straightedge, a feeler
gauge, and a good light. Figure 4(a) illustrates how to use a straightedge and a feeler gauge to check the
top surface of the cylinder block. Visually inspect the cylinder block for cracks, breaks, or other damage.
Measure the bore in the cylinder block, with a dial indicating bore gauge, to determine if wear or an outdetermine
of-round condition exceeds the manufacturer’s specification. Figure 4(b) illustrates the use of a bore
gauge to measure a cylinder bore. An inside micrometer can be used as well, but a dial indicating bore
gauge is easier to use.
Tests: A dye penetrant test should be conducted on the engine block’s surface to identify cracks that are
not identified by visual inspection.
Cylinders are provided with liners which may be of wet and dry type depending on whether water comes
into direct contact with liner or not. Cylinder liners have to be inspected if any of the following problems
have encountered: Excessive water in the lubricating oil, Oil in the cooling water etc.
Reasons for cracking, distorting of cylinder liners: poor cooling which causes hot spots on liners, Scale
formation due to improper cooling foreign bodies in the combustion space, or erosion and corrosion etc.
Visual inspection and tests:
Use testing method, such as the
water pressure test or air pressure
test i.e. passing pressurised air or
water through liners. To check
liners for leaks, fill it with
glycol-type antifreeze. This
liquid will leak from even the
penetrating dye to locate these
cracks is also possible.
Cylinder Head is mounted on the cylinder block and valves, spark plug etc. are fitted in it. The cylinder
head is held tight to the cylinder block by number of bolts or studs. Common problems in and on cylinder
head are: Cracks, Distortion and Warpage. Cracks in cylinder heads are located by either visual inspection
or dye penetrant test. Distortion may be caused by improper welding of cracks or by improper tightening
of the cylinder head studs. Repair of distorted or damaged cylinder heads is impossible. They should be
replaced as soon as possible.
Procedure for cleaning cylinder head:
1. Immerse the cylinder head into a dip or soak type of cleaning tank and allow it to soak until all baked
grease, oil and paint have been removed. Two hours are sufficient for this purpose.
2. Remove the cylinder head from cleaning tank and steam clean or rinse with hot water.
3. Blow out all the passageways with compressed air.
4. Place the head on some type of suitable stand or bench and san the cylinder head gasket surface with a
Piston: It receives the energy from the combustion of fuel and transmits it to the crankshaft. The piston
must withstand heavy stress under severe temperature extremes. It is a cylindrical component fitted into
the cylinder forming the moving boundary of the combustion
system. It fits perfectly into the cylinder providing a gas-tight
space with the piston rings and the lubricant. Piston wear is
affected by lubrication. An adequate supply of oil is essential
to provide the film necessary to cushion the piston and other
parts within the cylinder and prevent metal-to-metal contact.
Inadequate lubrication will cause piston seizure, and piston
pin busing wear. The pressure-recording instruments usually
give warning of low oil pressure before any great harm
results. Piston faces troubles due to improper cooling water
temperature. If an engine is not operated within the specified
temperature limits, lubrication troubles will develop. High
cylinder surface temperatures will reduce the viscosity of the
oil. As the cylinder lubricant thins, it will run off the surfaces.
The resulting lack of lubrication leads to excessive piston and
There are certain unavoidable troubles, such as cracked connecting rods caused by defective material.
Such cracks must be discovered before they develop to a point that the rod fails. Magnaflux testing is
considered the best method for locating cracks. If you discover a crack in a connecting rod, replace the
rod; do not try to repair it. If you have to replace a damaged rod, send it, with other damaged parts, to a
salvage center for possible reclamation. Do not repair defective connecting rod bolts, except for removing
small burrs by using a fine rectangular file. If you doubt the condition of a bolt or a nut, replace it. Check
the connecting rod bore for out-of-roundness with an inside micrometer. Make the correction and recheck
the bore. If the distortion is permanent, replace the rod. You can make plugged oil passages of connecting
rods serviceable by running a wire through them. In extreme cases, you may need to drill the passages
free of foreign matter.
Procedure for inspection of connecting rods:
1. Measure the rod end bore out of roundness with the help of snap gauge.
2. Rod big bore end should be measured with the help of snap gauge and inside micrometer in same
manner like small end. If big end does not meet specifications it should be reconditioned and replaced.
3. If it meets the specifications, it should be checked for straightness.
4. If rod is not straight, it should be replaced or reconditioned.