Valve train failures from broken or bent pushrods, valves, rocker arms and worn valve keepers and rotators in many instances could be caused by improper timing of the gear train. Depending on valve lash setting, if the camshaft gear is improperly timed by tooth early, the engine pistons will strike the intake valve heads. If the timing is set one tooth late, the exhaust valve may contact the pistons.
Engine Gear Train Timing Check Without Removing Front Cover or Engine Tear Down
For testing purposes only: No. 1 intake valve setting with No. 1 piston at TDC (compression) is 0.74 mm (0.029 in.). Method One uses a Feeler Gage.
Method One - Using a Feeler Gage
Follow these steps when using a feeler gage:
Adjust the No. 1 intake valve with the No. 1 piston set at TDC (Top Dead Center) compression stroke to 0.74 mm (0.029 in.).
Scribe a straight line or a radial line in a clockwise direction, 47 mm (1.850 in.) in length. Start from the vibration damper pulley notch when facing the engine. See Figure
Checking Engine Gear Train Timing
Turn the engine forward to approximately BDC (Bottom Dead Center).
Place a 0.10 mm (0.004 in.) feeler gage between the valve lever and valve stem of the No. 1 intake valve and slowly rotate the engine forward until the feeler gage becomes tight. This is now the point at which the No. 1 intake valve starts to open before top dead center. The scribed mark should line up with the TDC arrow located on the front cover, or be within 0.65 mm (0.260 in.) on either side of the arrow (equals 3.5 degrees).
One tooth out of time on the gear train equals approximately 11 degree movement, 21.431 mm (27/32 in.) radial distance, of vibration damper.
If the timing on the No. 1 valve is within specifications, the other valves, barring extreme camshaft lobe wear or poor adjustment, will also be in time.
The oil pressure relief valve (stamped with "FC") should be tagged upon removal. Do not mix the oil pressure relief valve with the oil pressure regulator valve (found in the side of the crankcase).
Remove the oil pressure relief valve from the front cover (rear half) and mark to identify its location. See Figure
The valve may be removed by depressing the plunger and trapping a length of copper wire when released. The valve may then be removed by pulling the copper wire.
1. Oil Pressure Relief Valve
2. Front Cover Rear Half
Oil Pressure Relief Valve
Cleaning Front Half of Front Cover
Follow these steps to clean the front half of the front cover:
Remove all gasket material and RTV from the front half of the front cover using a scraper or wire brush.
Clean all bolt threads prior to reassembly.
Inspection is particularly necessary if oil and coolant contamination has been found, and no other cause is discovered for the contamination.
Visually inspect the front cover for cracks or porosity.
Replace any front cover that fails visual inspection.
Gear Train Removal
Follow these steps to remove the gear train.
Rotate the engine so timing marks on the lower and upper idler gears, crankshaft and camshaft gear are aligned. See Figure
6. Upper Idler Gear
2. Rear Half Front Cover
7. Upper/Lower Idler Gear Timing Marks
3. Camshaft Gear with Timing Disk Plate
8. Air Compressor Gear Location
4. Cam Gear/Upper Idler Timing Marks
9. Lower Idler Gear
5. High Pressure Pump Gear Location
10. Lower Idler Gear/Crank Timing Marks
Once assembled at the alignment of marks position, the engine will require 37 crankshaft revolutions for the alignment position to be attained again.
Loosen and remove the idler gear retaining bolt using gear socket J 41167
Lower Idler Gear Removal
Remove the idler gear assembly from the front cover.
A new upper idler gear bolt must be used with each installation of the upper idler gear. There is a preapplied sealant on the new mounting bolt.
Each idler gear (upper and lower) are supported on tapered roller bearings and shafts. The bearing retaining nut should not be removed as it is required for torquing the nut. If the bearing is worn or loose, replace the complete gear assembly.
Install the front cover, front half using the following steps.
Apply assembly grease to the three O-rings and install into the front cover. See Figure
Front Cover Installation
Install a new gasket (3 segments) into the front half of the front cover. Two of the gasket segments are molded pieces and the third is a bulk piece. Once the gasket segments are in place, apply RTV to the joints.
Install the front cover on the locating dowel pins and install the mounting hardware.