The following sections cover engine disassembly and the visual inspection used to check for obvious engine damage. Useful information can be obtained from parts just as they are removed from the engine and before they are cleaned. Other information is obtained after the parts are cleaned.
Whenever an engine or component is dismantled, even if parts are being discarded, it is good practice to look for the cause of damage or wear.
Every parts of an engine gradually wear or deteriorate due to use, and this often depends on how the operated. Overloading, overheating, poor air filtration, poor lubrication, lack of maintenance, and neglect will all have an effect on engine life. The evidence indicating why a part failed or why there is a particular type of wear could point to operating conditions.
Cleaning engine parts
After you have removed all the parts from the engine block and cylinder lock and cylinder head, everything should be cleaned. Different cleaning techniques are needed depending upon part construction and type of material.
- Scrape off gaskets and hard deposits
Begin engine parts cleaning by scraping off all old gasket material and hard deposits. Scrape off the gaskets from the valve covers, head, front cover, intake manifold, oil pan, and other components. Also scrape off as much hardened oil and carbon as you can.
Use a dull scraper and work carefully when cleaning soft aluminum parts. The slightest nick, in cylinder head for instance, could cause head gasket leakage when return to service.
WARNING! When using gasket a gasket scraper, push the scraper away from your body, NOT toward your body. Scraper can inflict serious cuts
- Use cleaning solvent
After scraping off the gaskets, use cleaning solvent to remove hard to reach deposits. A hot tank is a large cleaning machine filled with strong, corrosive chemicals.
It will remove mineral deposits in the water jackets, hard carbon deposits, oil, grease and even paint. Automotive machine shops normally have a hot tank.
DANGER! Never use petrol to clean parts. The slightest spark or flame could ignite the fumes, causing a deadly fire!
- Use power cleaning tools
There is several power cleaning tools used by the professional mechanics. If used properly, they can speed up and ease engine repairs
A power brush is driven by an air or electric drill to remove hard carbon. It is especially handy inside hard to reach areas combustion chambers
DANGER! Always wear eye protection when cleaning parts with power tools. Metal bristles, bits of carbon, or metal chunks from tool or part breakage can fly into your face.
Cylinder head inspection
A cylinder head stand is used to hold the head off the workbench surface. After cleaning the cylinder head, mount it on stand. Then, inspect the cylinder head closely for problems. Look for cracks, burning, and erosion between combustion chambers. Also check the valve guides and seats for wear and damage.
- Measuring cylinder head war page
A warped cylinder head has a bent or curved gasket face, usually from engine overheating. Straight edge and feeler gauge are used to measure cylinder head war page. Lay the straightedge on the cylinder head.
Try to slip different thickness feeler gauge blades under the straightedge. The thickest gauge that fits equals the cylinder head war page. Check war page in different position across the cylinder head gasket face.
The most commonplace war page that shows up is between the two center combustion chambers.
- Surface grinding or milling cylinder head
Cylinder head surface grinding (sometimes milling) is an engine reconditioning shop operation where a thin layer of metal is taken from the gasket face of the cylinder head. It is carried out to correct head war page.
Before final inspection, make sure that the crankshaft is perfectly clean. Use compressed air to blow out all of the oil passages. Look at each connecting rod and main journal surface closely. Look for scratching, scoring and any signs of wear. The slightest nick or groove is very serious. A bent crankshaft can ruin new main bearings or cause the engine to lock up when the main caps are tightened.
Checking crankshaft alignment
To measure crankshaft straightness, mount a dial indicator against the center main bearing journal. The crankshaft can be mounted on v-blocks, or between centers.. Slowly turn the crankshaft while watching the indicator. Indicator movement equals crankshaft bend. If not within limits, renew the crankshaft or have it straightened and ground by an engine reconditioning shop.
Camshaft inspection involves measuring cam lobe and journal wear. It also includes distributor oil pump gear inspection and camshaft bearing measurement or replacement.
- Measuring camshaft wear
If wear shows across the full width of the cam, and excessive wear of the cam lobe has taken place, a new camshaft should be installed. The valve should also be checked. On OHV engines, the cam lift can be checked with the camshaft in the engines. The height of the lobe can also be measured with a micrometer, with the camshaft removed from the engine.
- Checking a camshaft
Check for alignment by rotating the camshaft in vee blocks and using a dial gauge to check for eccentricity. Journal diameters should be checked with a micrometer, and the bearings with a telescopic gauge. The two dimensions can then be compared to determine whether bearings are worn.
Pistons are made of aluminum, which is very prone to wear and damage. It is very critical that each piston be checked thoroughly. Look for cracked skirts, worn ring grooves, cracked ring lands, piston pin bore wear, and other problems. You must find all trouble that could affect piston performance and engine service life.
- Measuring piston wear
A large outside micrometer is used to measure piston wear. Micrometer readings are compared to specifications to find wear. Piston size is measured on the skirt, just below the piston pinhole. Adjust the micrometer for a slight drag as it is pulled over the piston. If worn more than specifications renew the piston.
Connecting rods inspection
Connecting rods are subjected to tones of force during engine operation. As result, they can wear, bend, or even break. The old piston and the bearing inserts will indicate the condition of the connecting rods. If any piston or bearing wear abnormalities are found, there may be problem with the connecting rods.
Checking connecting rod straightness
To determine if a connecting rod is bent, a special connecting rod alignment fixture is needed. It will check whether the connecting rod small end and big end are perfectly.
Connecting rod small end service
Measure the connecting rod small end with a telescoping gauge and micrometer
Connecting rod big end service.
To check the connecting rod big end for problems, remove the bearing insert and bolt the connecting rod cap to the connecting rod. Any difference in edge diameter (side to side) equals connecting rod big end taper. Any difference in the cross diameters equals’ connecting rod big end out of roundness.
Timing belt inspection
Inspect the timing belt for signs or deterioration (cracks, hardening, softening, fraying). When severe timing belt damage is found, inspect for mechanical problem. Check sprocket condition and installation. Make sure no leaking oil can reach and ruin the belt. Turn the tensioned wheel, to make sure its bearing spins freely. Correct any trouble that could reduce timing belt life.
Replacement of the engine components
The visual checks made during dismantling, and the measurements taken during inspection, will determine which parts are serviceable and which parts are unserviceable. Unserviceable parts will have to be renewing, reconditioned or repaired. In many cases, particularly with smaller parts and components, a new (replacement) part will be obtained and fitted.
- Replacing the crankshaft
If the crankshaft is worn beyond the specification or damage in some way, it will require replacement. In order to provide a better service life for engines, a number of manufacturers have published guidelines for reusing crankshaft and bearings in their engines. Whenever a crankshaft is to be replaced, the timing gear attached to the front of the shaft will need to be refitted, as it is not a standard part of the crankshaft.
- Replacing the timing belt
During the engine operation, the belt wears, and at specified service internals it must be replaced. The majority of timing belts require changing at 100 000 Km. A general procedure for changing a timing belt is as follows:
- Release the belt tensioned mounting bolts and pull the tensioned away from the belt.
- Remove the belts.
- Fit the new belt to the pulleys, making sure the timing marks are still aligned.
- Allow the tensioned to tension the belt by means of its tensioning spring.
- With spring tension being applied to the tensioned pulley, rotate the engine two revolutions so as to remove all the slack out of the belts.
- Recheck the timing mark alignment then secure the tensioned in place. If incorrect, repeat the above procedure.
- Refit the timing belt cover.
- Replacing the valve seals and springs
On some engines, the valve stem seals and spring can be removed and installed without removing the cylinder head from the engine. An adaptor is fitted to the spark plug hole and airline connected. Compressed air then applied to the cylinder to hold the valve against its seat, and special tool is used to depress the valve spring.
- Replacing camshaft bearings (OHV engines)
With a special bearing remover, bearings can be removed from the engine block. The remover bar is inserted through the bearings, puller sleeves being installed on the bar at each bearing. When the remover handle is turned, the bearings are pulled from their bores in the crankcase. By a similar action, new bearings are installed.
Many parts of a motor vehicle, such as engine blocks, pistons, crankshaft, gears, axles, etc can crack during service. During overhauls, parts should be thoroughly cleaned and visually inspected for signs of cracking. Pay particular attention to such areas as cylinder head valve ports, cylinder walls, block water jackets, and pistons. Cracks or fractures may be grouped in three types:
- Cracks plainly visible to the eye.
- Cracks so fine as to be invisible without detection equipment.
- Internal cracks that do not reach the surface.
Crack detection methods
There are a number of techniques used to check for the presence of cracking including X-ray, magnetic, fluorescent, dye penetrates, and combinations of these techniques. The X-ray techniques require expensive equipment and are only used in large specialty shops.
- Magnetic field with iron powder
A powerful magnet (can be a permanent or an electromagnet) is placed across an area suspected of containing a crack. A fine iron powder is then dusted over the area. The metal under the feet of the magnet becomes heavily magnetized. A crack will interrupt or break this magnetic field enough to cause the iron powder to collect along the crack. The magnet should be moved into the different positions. The process works best when the crack is at the right angles to the magnetic field
- Magnetic field with fluorescent ferromagnetic particles
This method also requires that a strong magnetic field be set up in the part. A special solution that contains fluorescent ferromagnetic particles is then sprayed on the area to be tested. As with iron powder, the ferromagnetic particles are attracted to and along the crack line. When exposed to a black
Light (invisible ultraviolet rays), the particle packed along the crack line will glow white while the reminder of the part will remain blue-black. Black light (ultraviolet rays) is not harmful to skin or eyes.
- Fluorescent penetrant
This method involves the use of a special fluorescent penetrate (liquid that readily enters even finest cracks). The area to check is first cleaned with a patented cleaner. Then the fluorescent penetrate is sprayed over the area.
- Dye penetrant
Dye penetrant, when exposed to a developer, will show as a bright red stain line against a whitish background. The part is cleaned, penetrate applied, surplus penetrate removed, and developer sprayed on. Note the red stain lines indicating cracks between the gear teeth.