859116 Mercruiser NUT, (.437-20), BELL HOUSING STUD

Measure the valve lash between the rocker arm and the valve bridge. Perform the adjustments with the engine stopped. The valves must be fully closed. To determine whether the valves are fully closed, refer to Testing and Adjusting, "Finding the Top Center Position for the No. 1 Piston" and Testing and Adjusting, "Crankshaft Position for Valve Lash Setting".
Incorrect adjustment of the valve bridge and/or of the valve lash can result in engine damage from these conditions: excessive exhaust temperatures, incorrect seating of the valves and contact between the valves and the piston.
Ensuring Proper Valve Lash
Is critical for engine operation that the valve lash is properly set prior to engine start and loading. Misadjusted lash on a standby genset engine can result in the engine shutting down shortly after startup, due to false detonation signals from a noisy valve train. To ensure that the lash has been properly set, perform the following procedure:
Set the lash according to Valve Lash Adjustment section.
After the lash has been set, run the engine at 1800 RPM with no load for at least 35 minutes.
Using Cat ET monitor the engine detonation signals. If the detonation level of any cylinder exceeds 50% for any length of time, there may be a lash setting problem. Refer to the following table to determine and note what valves should be reviewed and adjusted to reduce the detonation signal.
Table 2
G3520 Valve Overlap With Detonation Sensors
Cylinder Intake Valves Exhaust Valves
1 6 - 13 - 14 9 - 10 - 19 - 20
2 13 - 14 9 - 10 - 17 - 20
3 None 5 - 6 - 17 - 18
4 None 5 - 6 - 13 - 18
5 7 - 8 - 19 - 20 3 - 11 - 12
6 4 - 7 - 8 - 15 - 16 - 19 5 - 9 - 17 - 18 - 19 - 20
7 1 - 2 - 11 13 - 14
8 1 - 2 - 11 - 12 14
9 3 - 4 - 12 - 15 None
10 3 - 4 - 15 - 16 1
11 14 9 - 10 - 17 - 18
12 None 5 - 8 - 10 - 17
13 8 - 9 - 19 - 20 3 - 4 - 12
14 9 - 10 - 19 - 20 3 - 4 - 15
15 1 5 - 6 - 13 - 14
16 1 - 2 6 - 13 - 14
17 4 - 7 - 15 - 16 1 - 2
18 7 - 8 - 15 - 16 1 - 2 - 11
19 2 - 3 - 11 - 12 None
20 3 - 4 - 11 - 12 None
If any valves do require adjustment, turn off engine and allow the engine to coast to a stop. Wait at least 30 minutes to allow the intake and exhaust valves to cool. Set the lash to the standard values.
Once lash has been adjusted start engine and run at 1800 RPM no load for at least 35 minutes. Check detonation levels to ensure that all detonation levels are below 50%.
If adjusting valve lash did not bring the detonation levels to an appropriate level, then you may have a more serious hardware issue. Visually inspect all valve train components to ensure that there are no visibly damaged parts.Valve Bridge Adjustment
Illustration 1 g03509419
(1) Valve cover
(2) Transformer
Remove valve covers (1). If a seal is damaged or deteriorated, obtain a new seal for assembly.
Remove transformer (2). If the O-ring seal is damaged or deteriorated, obtain a new O-ring seal for assembly.
Illustration 2 g03509186
(3) Locknut
(4) Adjustment screw
(5) Rocker arm
(6) Valve bridge
Loosen locknut (3) and adjusting screw (4).
Press straight down on rocker arm (5) at the contact point for valve bridge (6). Turn adjusting screw (4) clockwise until the screw just contacts the valve stem.
Tighten adjusting screw (4) for an additional 25 5 degrees in order to straighten the valve bridge onto the dowel.
Hold adjusting screw (4) in position and tighten locknut (3) to 30 4 N m (22 3 lb ft).
Make sure that the valve lash is correct. Refer to "Valve Lash Adjustment".
Make sure that O-ring seal is in good condition and install the transformer (2) .
Make sure that seal is in good condition and Install valve cover (1).Valve Lash Adjustment
The valve bridge must be adjusted before the valve lash is adjusted.
Ensure that the No. 1 piston is at the top center (TC) position. Refer to Testing and Adjusting, "Finding the Top Center Position for the No. 1 Piston".
Work on the appropriate cylinders that are listed in Testing and Adjusting, "Crankshaft Positions for Valve Lash Setting".
Before you perform any adjustments, use a soft hammer to tap lightly on each rocker arm at top the adjustment screw. This action will ensure that the lifter roller is seated against the camshaft.
Illustration 3 g03511179
(1) Hydraulic lash adjuster
(2) Locknut
(3) Adjustment screw
Loosen locknut (2) and adjusting screw (3).
With light force turn the adjustment screw (3) clockwise until the ball is seated into the cup of the hydraulic lash adjuster (1). Once contact is made, rotate the adjustment screw (3) clockwise an additional 360 45 degrees.
Hold adjusting screw (3) in place and tighten locknut (2) to a torque of 70 15 N m (52 11 lb ft).