1980/08/13 Caterpillar

3408 And 3412 Marine Engines

SUPPLEMENT: 11/25/81

ENGINE NEWS; AUGUST 13, 1980, PAGES 2 AND 3.

In the article, "Two New Front Power Take-Off Groups Are Available," under the subject, "Service Information," change the first paragraph to read as follows:

"During reconditioning, install the clutch assembly on the tapered shaft and tighten the nut to move the clutch assembly to its seat. The nut must be tightened to 41 N·m (30 lb ft) plus 60° to 90° for single-disc clutches and 41 N·m (30 lb ft) plus 120° to 150° for double-disc clutches. Bend a tab on the lock against a flat on the nut."

--------------- END SUPPLEMENT ---------------

Two new front power take-off groups are available for use on 3408 and 3412 Marine Engines. The 5N7399 Front Power Take-Off Group has a single-disc clutch, and the 5N7400 Front Power Take-Off Group uses a double-disc clutch.

Both of these new front power take-off groups use two bearings, which are kept apart by spacers, in front of the clutch. This design keeps the clutch on the same center line as the crankshaft without the need for a crankshaft pilot bearing or an external bearing.

The result is less vibration between the clutch and crankshaft, which can cause a clutch failure.

Formerly, a pilot bearing was used. Later clutches did not have a pilot bearing. Instead, a longer shaft and an external bearing were used.

Alignment Of Front Power Take-Off Groups

Correct alignment of the new front power take-off groups is very important. The new groups' alignment is controlled by the runout (full indicator movement or tota indicator reading) of the adapter and bore-to-crankshaft center line, and the runout of the housing pilot and face in relation to the clutch shaft center line. Since the factory tolerances control the alignment of the parts, they control the alignment of the front power take-off group with the crankshaft. Correct installation prevents alignment changes.

The earlier groups' alignment was controlled by either the pilot or external bearing.

It is Caterpillar's recommendation that the steps which follow be used during installation, to make sure the front power take-off group is in correct alignment with the engine. If the front power take-off group was a separate purchase and did not come installed on the engine, begin with Step 1. If the front power take-off group came as an installed attachment, begin with Step 6.

1. With the engine installed in the boat, install the 5N7751 Adapter with eight S1573 Bolts tightened to a torque value of 115 ± 15 N·m (85 ± 11 lb ft) and install the 3L8029 or 4B4805 Drive Ring with eight S1591 Bolts.

2. Put a dial indicator in position to read the total vertical movement of the crankshaft at the top of the drive ring. Use a lever to move the drive ring and crankshaft upward and read the indicator total movement. do not put force against the adapter housing because it will move the dial indicator base.

3. Fasten the base for the dial indicator to the drive ring. Put the indicator in position to read the runout of the adapter bore. Turn the crankshaft and write the indications for 0°, 90°, 180° and 270°. Add one-half the indication from Step 2 from the indication at 180°. With the adjusted values at 0° and 180°, there must not be more than 0.36 mm (.014") difference between any two of the four points measured.

4. With the base still fastened to the drive ring, move the dial indicator to read the face edge of the adapter. Turn the crankshaft and read the runout. The runout must not be more than 0.41 mm (.016").

5. If Steps 3 and 4 are not in an acceptable specification range, loosen the bolts and adapter, and tighten the bolts again, to 115 ± 15 N·m (85 ± 11 lb ft). Do Steps 3 and again. If the indications still are not acceptable, replace the adapter and/or drive ring. If the indications are acceptable, install the remainder of the group, including the 5N6958 Channel.

6. Fabricate and install the structure to which the 5N6958 Channel will be fastened. It is best to make the structure no more than 6.35 mm (.25") lower than the channel.

7. Put a dial indicator under the end of the front power take-off shaft and move the setting to "0". Measure the gap between the 5N6958 Channel and the structure you fabricated in Step 6.

8. Put shims, equal in thickness to the width of the gap, between the channel and structure and fasten the channel to the structure with bolts.

When the bolts are tight, read the dial indicator. If the shaft has moved more than 0.05 mm (.002"), loosen the bolts and add the necessary thickness of shims. Tighten the bolts.

Service Information

... During reconditioning, when the clutch assembly is installed on the taper shaft, tighten the nut to 41 N·m (30 lb ft) to move the clutch assembly to its seat. Bend a tab on the lock against a flat surface on the nut.

... The correct torque for the front spanner nut which holds the tapered roller bearings is 750 ± 68 N·m (550 ± 49 lb ft).

... The correct force needed on the control lever to engage the clutch is 467 ± 58 N (107 ± 13 lb) at 541 mm (21.3") or 260 ± 30 N·m (190 ± 22 lb ft) for the double-disc clutch in the 5N7400 Front Power Take-Off Group and 605 ± 67 N (136 ± 15 lb) at 345 mm (13.6") or 210 ± 23 N·m (155 ± 17 lb ft) for the single disc clutch in the 5N7399 Front Power Take-Off Group.

To adjust the clutch, remove the name plate from the housing, and turn the shaft until there is access to the adjustment pin. Release the adjustment pin and turn the adjustment ring clockwise to increase the necessary torque. To decrease the necessary torque, turn the adjustment ring counterclockwise.

Engage the adjustment pin and install the cover on the housing.