1674 DIESEL TRUCK ENGINE Air Induction And Exhaust Systems Caterpillar

Air Induction And Exhaust Systems
1.1. Air Cleaners (Caterpillar Dry-type Air Cleaners Only)
2.1. Restriction Of Air Inlet And Exhaust
3.1. Filter Element Cleaning: (Caterpillar Dry-type Filter Elements Only - If Other Manufacturer's Air Cleaner Is Used Refer To Their Recommendations)
4.1. Valve Lash Setting
5.1. Compression Check
6.1. Crankcase Pressure
7.1. Turbocharger

The purpose of the air induction system is to provide clean air to the engine in an efficient, silent manner while the exhaust system discharges exhaust gases as quickly and as silently as possible. Engine horsepower and efficiency will be reduced if either the air inlet or exhaust becomes restricted. Good maintenance practice cannot be over emphasized.

Air Cleaners (AVSpare Dry-type Air Cleaners Only)

Regular service intervals, along with close visual inspection of the air cleaner, are necessary for proper cleaning of the engine inlet air. The service interval will vary with the weather and working conditions. Where dust conditions are severe, it will be necessary to service the air cleaner frequently. In damp weather and other conditions of little or no dust, the service interval can be extended.

To extend the service life of the element, the exhaust and air cleaner inlet pipes should be arranged so that exhaust and/or oil fumes do not enter the engine air cleaner.

Visual inspection of the gaskets and seals is important in keeping dust from by-passing the air cleaner. Any dirt allowed to enter, accelerates wear throughout the engine. If the condition of any of the replaceable seals and gaskets is questionable, replace them. If the sealing ends of the filter element or the element pleats are damaged, replace the element.

Extra filter elements should be kept on hand for replacement or for use in the air cleaner while the element that was removed is being cleaned.

When equipped with a dry-type air cleaner, a service indicator similar to the one shown is available.

The air cleaner service indicator is connected to the air inlet pipe between the air cleaner and the turbocharger. It contains a red marked piston, which gradually rises with restriction to the air flow. When the entire piston is visible it will lock in this position. This indicates a need for air cleaner service. The piston will remain in this position whether or not the engine is running. After servicing the air cleaner, reset the piston by depressing the plunger in the bottom of the indicator.


Excessive engine exhaust smoke and/or loss of power may indicate the need for servicing the air cleaner. Never service the air cleaner while the engine is running.

SINGLE STAGE AIR CLEANER FILTER ELEMENT: Every 10,000 miles, in average operating conditions, remove the filter element for inspection and cleaning. This period may be extended in clean atmosphere and can only be determined by experience.

1. To remove the filter element, loosen the wing nut, remove the end cover and the filter element.
2. Inspect the element and if it is damaged, install a new element.
3. Remove any dirt which has accumulated on the bottom of the case and clean the filter element using one of the methods covered in the topic, FILTER ELEMENT CLEANING.


4. Install the filter element and cover. When installing the filter element, the closed end of the element must be installed against the cover. Fasten the cover securely.

Restriction Of Air Inlet And Exhaust

If an air inlet restriction is suspected in the piping or air filter element, check with a differential pressure gauge or manometer. Remove the air cleaner service indicator and connect differential pressure gauge or manometer in the service indicator connection. The air inlet piping or air cleaner should not restrict air flow more than 30 inches (762 mm) of water difference in pressure.


Restriction of the exhaust system (back pressure) is measured with a differential pressure gauge or manometer. This pressure difference is measured between the turbocharger outlet and ambient air and should be no more than 20 inches (645 mm) of water. An exhaust pressure tap is provided in the turbocharger outlet elbow. This check should be performed with the engine at operating temperature and developing full rated power.


Filter Element Cleaning: (AVSpare Dry-type Filter Elements Only - If Other Manufacturer's Air Cleaner Is Used Refer To Their Recommendations)

Filter elements can be cleaned several times before replacing; however, close inspection of the element should be made when reinstalling a cleaned element.

The ends of a filter element will be damaged by bumping or tapping. Bent and/or dented ends cannot seal properly and may allow unfiltered air to enter the engine cylinders and cause premature engine wear.

Clean the filter element using one of the following methods:

CLEANING WITH PRESSURE AIR: Using clean, dry air, at a pressure not to exceed 30 PSI (2 kg/cm2), proceed as follows:

Hold the air nozzle at least one inch from the element and direct air at an angle against the inside (engine side) of the element to loosen any imbedded dirt. Best results can be obtained by moving the air hose so that air is directed at an angle along the complete length of each pleat.

Blow off loose dirt by directing air against the outside of the element. Repeat this procedure until the element is clean. Make certain that no dirt is inside the element.


CLEANING WITH WATER: Using clean water, at a pressure not to exceed 40 PSI, proceed as follows:

Direct water at an angle against the inside (engine side) of the element to loosen any imbedded dirt. Best results can be obtained by using a water hose without a nozzle and moving it so that water is directed at an angle along the complete length of each pleat. Wash off loose dirt by directing water against the outside of the element. Repeat this procedure until the element is clean. Make certain that no dirt is on the engine side of the element, and thoroughly dry the element before installing it.


CLEANING WITH DETERGENT: Some oily and/or sooty deposits can be removed by washing the element in a solution of warm water and a good household non-sudsing detergent. Rinse with clean water and thoroughly dry the element before installing it.



1. Hold a lighted electric bulb inside the dried element and carefully inspect the element for tiny, pinpoints of light. Any light showing indicates a pleat has ruptured and will tear with further use. Discard the element.
2. Wrap usable elements in sealed plastic bags.
3. Store the wrapped element in a dry, clean place.


When equipped with oil bath type air cleaners, accumulation of dirt and/or oil in the air cleaner outlet pipe is an indication the air cleaner is not being serviced or functioning properly. Refer to manufacturer's recommendations for servicing.

Valve Lash Setting

Check Valve Lash Setting With Engine Stopped:

1. Remove the flywheel timing cover from the flywheel housing. Rotate the engine flywheel in direction of engine rotation, so the flywheel timing pointer is at the TC 1-6 cyl. mark on the flywheel. Remove the bolt from the flywheel timing hole and insert timing bolt (long bolt which fastens cover to flywheel).

2. Remove the valve cover and observe the positions of the No. 1 and No. 6 cylinder valves and the camshaft lobes to determine which cylinder is sealed for compression.
3. Turn adjusting screw counterclockwise 2 clicks or more to provide clearance between rocker assembly and valve.
4. Turn adjusting screw clockwise to obtain zero lash. There should be no free rocker movement or adjusting screw button lateral movement.


NOTE: The adjusting screw button can still be rotated by finger pressure even when it is in contact with valve stem and clearance is zero. Turning the adjusting screw clockwise beyond this point will force the valve off its seat, and final lash setting will be incorrect.


5. Turn adjustment screw counterclockwise ten clicks (.020 in.; 0,50 mm) for exhaust valves and four clicks (.008 in.; 0,20 mm) for inlet valves. One click is equal to .002 in. (0,050 mm). All exhaust and inlet valve clearance can be adjusted by positioning the flywheel only twice. After adjusting half of the valves, rotate the engine 360° in direction of normal rotation and adjust the remaining half. If No. 1 cylinder is in compression, adjust the inlet valve clearances for cylinders 1, 2 and 4, and the exhaust valve clearances for cylinders 1, 3 and 5. If No. 6 cylinder is in compression, adjust the inlet valve clearances for cylinders 3, 5 and 6 and the exhaust valve clearances for cylinders 2, 4 and 6.

Compression Check

The following procedure provides a check of the sealing ability of the individual valves and piston rings without removing the cylinder head:

1. Remove the fuel injection nozzle from the suspected cylinder, leaving the precombustion chamber in place.
2. Adapt an air hose to the precombustion chamber. This can be done with either a threaded fitting or by holding a rubber adapter in place.
3. Rotate the crankshaft until the piston in the suspected cylinder is at top center (TC) on the compression stroke. In this position the valves of this cylinder are closed.


Lock engine to prevent crankshaft rotation.

4. Force air into the cylinder and then check for escaping air. Air escaping from the exhaust opening indicates exhaust valve leakage. Air escaping from the air cleaner inlet indicates inlet valve leakage. If air escapes from the crankcase breather during this test, the piston, rings and/or liner can be at fault.

It may be necessary to remove inlet and outlet connections on both sides of the turbocharger to notice leakage from inlet and/or exhaust valves.

An alternate and more accurate method of checking compression can be made with the use of an air regulator valve, gauges and an adapter group. Authorized dealers have the necessary equipment and can perform this service for you or supply you with the necessary instructions.

Crankcase Pressure

Excessive crankcase pressure can be a result of combustion gas leaking past broken or damaged pistons, worn cylinder liner walls and/or piston rings. This condition will usually be accompanied by irregular engine operation and excess fumes from crankcase breather opening. This pressure can cause the breather element to become restricted in an unusually short time. In addition, it can cause engine oil to leak past gaskets and seals that would function properly under normal conditions.


Every 200,000 miles or if any unusual sound or vibration in the turbocharger is noticed, a quick check of bearing condition can be made without disassembling the turbocharger. This can be done by removing the piping from the turbocharger and inspecting the compressor impeller, turbine wheel and compressor cover. Rotate the compressor and turbine wheel assembly by hand and observe by feeling excess end play and radial clearance. The rotating assembly should rotate freely with no rubbing or binding. If there is any indication of the impeller rubbing the compressor cover or the turbine wheel rubbing the turbine housing, recondition the turbocharger or replace with a new or rebuilt one.

End clearance is best checked with a dial indicator. Attach a dial indicator with the indicator point on the end of the shaft. Move the shaft from end to end making note of the total indicator reading.

End play should be between .003 in. (0,076 mm) and .008 in. (0,203 mm). If end play exceeds .008 in. (0,203 mm) rebuild or replace the turbocharger. End clearance less than .003 in. (0,076 mm) could indicate carbon build-up on the turbine wheel and should be disassembled for cleaning and inspection.


A more reliable check of bearing condition can be made only when the turbocharger is disassembled and the bearings, shaft journal and housing bore diameters can actually be measured. This service is available from an authorized dealer.

Radial clearance can also be checked with a dial indicator. Remove the oil return line from the turbocharger. Attach a dial indicator with an extension indicator point long enough to contact the shaft through the oil return hole. Make sure the contact point is centered on the shaft (highest indicator reading). Raise both ends of the shaft all the way then push down in the opposite direction. Total movement of the indicator should be between .005 (0,13 mm) and .009 (0,23 mm). If radial clearance exceeds .009 (0,23 mm) or minimum clearance is under .005 (0,13 mm), the turbocharger should be disassembled and the bearings checked.

NOTE: Care must be taken not to cock the shaft or a false reading will be obtained.


If a turbocharger fails, try to determine cause of failure and eliminate before installing a rebuilt or new turbocharger. When installing a new or rebuilt turbocharger always perform the following steps.

A. Inspect the air induction and exhaust system for the presence of foreign particles which could result in repeat failure.
B. Change the air cleaner element.
C. Change the oil filters.
D. Drain and refill the engine crankcase.
E. Pre-lubricate the replacement turbocharger by filling the center housing with oil.