Use of 4C8753 Extended Collet{1250} Caterpillar

Use of 4C8753 Extended Collet{1250}

Usage:

3500 Family Engines

Introduction

(1) 4C8753 Extended Collet

The 4C8753 Extended Collet (1) is designed for use with the 8T1000 Electronic Position Indicator Group, or a dial type indicator, to increase the accuracy of the fuel setting adjustment for all 3500 Family Engines. Use the 4C8753 Extended Collet instead of the 5P4814 Collet for the fuel setting adjustment procedure for all 3500 Family Engines.

Use of the 4C8753 Extended Collet prevents side loading of the probe shaft by the fuel stop lever in the governor. This side loading can cause fuel setting errors, and breakage of the contact point on the indicator.

Carefully follow the procedures given in this publication, to ensure correct operation of the 4C8753 Extended Collet. Correct operation of the collet is necessary to obtain accurate results when performing the fuel setting adjustment for 3500 Family Engines.

Do not perform any procedure, outlined in this publication, or order any parts until you read and understand the information contained within.

Reference: Service Manual.

Operational Check for the 4C8753 Extended Collet

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NOTICE

If the probe shaft and contact point extension are not straight, they can drag in the tube of the extended collet and cause binding that will result in inaccurate readings. Before using the 4C8753 Extended Collet on an engine, do the operational check procedure that follows.

(1) 4C8753 Extended Collet. (2) 5P7263 Indicator Contact Point. (3) 8T1002 Probe.

1. Thread 5P7263 Indicator Contact Point (2) [76.2 mm (3.00") long] into the end of 8T1002 Probe (3) (part of 8T100 Electronic Position Indicator Group), or dial indicator shaft, until it is finger tight.

2. Examine the threaded end of the 5P7263 Indicator Contact Point (2) to make sure it is seated against the end of the probe shaft, or the indicator shaft.

NOTE: If the indicator contact point will not tighten enough so it is against the end of the 8T1002 Probe shaft, refer to the topic entitled Correcting the Cause of a Sticking Contact Point in this publication.

3. Slide 4C8753 Extended Collet (1) over 5P7263 Indicator Contact Point (2) and the probe shaft or indicator shaft. Tighten the nut on the extended collet to hold it in position on the stem.

4. Before using the tools on the engine, assemble the parts together as shown and check to make sure the contact point will move freely and does not stick or bind inside the extended collet.

5. Press on the end of the contact point so it will go IN as far as possible, then slowly release it. The contact point should come OUT, all the way, without stopping. It should not be necessary for the contact point to be pulled out because of binding or sticking.

If the contact point sticks when using a dial indicator, try another dial indicator. If the contact point sticks when using a 8T1002 Probe, refer to the topic entitled Correcting the Cause of a Sticking Contact Point in this publication.

Correcting the Cause of a Sticking Contact Point

If the 8T1002 Probe shaft is sticking in the 4C8753 Extended Collet, it may be because of the reasons that follow.

1. The 5P7263 Contact Point is not correctly seated against the end of the probe shaft (there is an air gap between the end of the probe shaft and the contact point).

2. The 8T1002 Probe shaft is not counterbored. This will prevent the contact point from fitting tightly against the end of the probe shaft. (This may be the reason for problem No. 1.)

3. The end of the 8T1002 Probe shaft is not square.

4. There is either a burr or a retaining compound on the threads in the end of the probe shaft.

5. The 5P7263 Contact Point is not straight.

To identify the cause of the problem, first remove the 4C8753 Extended Collet from the probe shaft. Make sure the probe shaft is free to move easily within the body of the 8T1002 Probe, without the extended collet being installed. If the probe shaft does not move freely, the probe must be replaced.

If the probe shaft does move freely within the probe body, rotate the probe shaft while watching the contact point tip. The tip should remain in one place and not move from side to side.

Movement of the contact point tip while the shaft is being rotated is an indication of a crooked shaft/tip combination. This is usually caused by misalignment where the two pieces join together. Misalignment may be caused if the contact point will not thread far enough into the probe shaft, so the two surfaces can contact each other.

On the threaded end of the 5P7263 Contact Point the threads do not usually go all the way to the contact point body. This then requires that a counterbore be added to the end of the probe shaft.

Look at threaded hole (A) in the end of the probe shaft. If hole (A) has threads all the way out to the end of the shaft, the end of the shaft must be modified by the addition of a counterbore in hole (A). Refer to the topic entitled Modification of Probe Shaft.

NOTE: Later 8T1002 Probes already have the needed counterbore and no modification will be necessary.

If the probe shaft has a counterbore and the contact point is still crooked, use a 4-48 thread tap to clean the internal threads in the probe shaft.

Remove any burrs on the end of the probe shaft. Do this by using a drill and drill bit to add a chamfer to the counterbore hole at the end of the probe shaft. If the contact point still does not appear to be straight, it is possible that the end of the probe shaft is not flat, and square with its length.

If the end of the probe shaft is not flat and square with its length, do one of the following:

* With a file positioned at a 90° angle to the length of the probe shaft, file straight across the end of the probe shaft. Turn the probe shaft to a new position and again file across the end of the shaft. Continue this procedure until the end of the shaft has been turned 360°, then again check for contact point straightness.

* Send the 8T1002 Probe to a machine shop to have the end made flat and square with its length.

* Replace the probe.