7231 Marine Transmission Testing And Adjusting


Clutch Hydraulic System

The oil must be near the normal temperature of operation between 150° to 160°F (65° to 71°C) when tests are made.

The clutches neet no adjustments. They adjust automatically to wear. If a clutch will not engage, either the clutch has a defect or the oil pressure from the oil pump is not enough to hold the clutch engaged.

Operation Test

A new element must be installed in the oil filter housing before any test for the hydraulic system is to be made.

Remove the plug, near the oil hose to the oil cooler, from the control valve. Install an 8M2886 Gauge (0 to 600 psi) and a 5S4648 Hose in the opening in the control valve, where the plug was removed.


Start the engine. Make a record of the pressure indication from the gauge when the control valve is put in either FORWARD or REVERSE position. The pressure to engage a clutch is 245 to 260 psi (1690 to 1790 kPa) in both positions. The minimum pressure must be 55 psi (380 kPa) when the control valve is in the NEUTRAL position.

If the oil pump is in good condition and it is necessary to adjust the pressure to engage a clutch, spacers (1) under springs (2) in relief valve (3) can be added to increase the pressure, or removed to decrease the pressure. See the chart below.

1. Spacers. 2. Springs. 3. Relief valve.

Come-Home Feature

If the marine transmission clutch can not be engaged and there is no way to get the vessel back to port, the come-home feature is used. The ahead clutch can be engaged by the force of three bolts that are put into the rear pressure plate of the clutch. With the correct torque on the bolts, the clutch is kept engaged until the bolts are removed. Bolts cannot be put into the pressure plate for the reverse clutch.


Use the come-home feature only when there is an emergency. When the hydraulic pump can not make enough oil pressure for lubrication, the engine (and marine transmission) must be run at low rpm.

1. The engine must be warm before using the come-home feature (a warm engine is not as much load as a cold engine when it is started).

2. Stop the engine. Remove cover (1) from the marine transmission.

3. Remove oil line (2) and bearing cap (3).

1. Cover.

4. On transmissions with 1/2" - 13 holes, install 1/2 - 13, 1.50 in. (38.1 mm) bolts (4) in the tapped holes of the clutch pressure plate. Alternately tighten the bolts to 65 ± 5 lb. ft. (90 ± 7 N·m).

On transmissions with 3/8" - 16 holes, install a 3/8 - 16, 1.50 in. (38.1 mm) bolt (4) in each of the three holes with threads, in the pressure plate. First tighten the bolts to a torque of approximately 15 lb. ft. (20 N·m). Next tighten each bolt again to a torque of 32 ± 5 lb. ft. (43 ± 7 N·m).

2. Oil line. 3. Bearing Cap.

5. Install bearing cap (3) and cover (1).

6. Be sure the level of the oil in the marine transmission is above the full mark on the gauge.

7. Start the engine.

4. Bolts.


The starter motor now has more load (the marine transmission and the propeller are the added load) when it starts the engine and can soon get hot. If the engine does not start in just a few seconds, turn off the starter switch and let the starting motor get cool before using it again. Also remember the propeller can move the vessel as the engine is started.

8. Run the engine (and marine transmission) at low rpm because of the problem of not much lubrication.

9. Stop the engine to stop the propeller.

10. With the engine stopped, remove cover (1), bearing cage (3) and three bolts (4). Install oil line (2), bearing cape (3) and cover (1).

NOTE: If the come-home feature was used for a long time, the recommendation is to make a thorough inspection of the bearings and the clutch plates and discs in the ahead clutch.

Vessel either Pulled or Pushed

Keep the propeller stopped when the vessel is either pulled or pushed with a stopped engine. The motion of the vessel can turn the propeller and there is no lubrication for the bearings, gears and clutch discs that turn with the propeller.

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