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The Gentleman's Express: Tech-Tips from the JIOC

Table of Contents

Lucas Fan Motor Repairs

Author: TECH

There comes the time when one of those fans ceases to operate even when supplied with the necessary power. Chances are that the brushgear is worn out. So let’s get it overhauled. First, disconnect the supply lead, then remove the fan motor, fan assembly and support spider as a unit from the shroud - 7/16" socket and ratchet. At the bench, dismount the fan from the motor (setscrew). Some WD-40 may be useful to release the shaft. If it is stubborn, press it out (don’t hammer it out or you’ll be SORRY you did!) Undo the bolts holding the motor to the spider.

Now, inspect the motor unit. At the shaft end, is there noticeable sideways play between the shaft bushing and the housing? If so, we need a new motor so call your local Lucas dealer and get a P/ N 78550. These newer motors are slightly different from the original, having an axial adjustment screw on the base end of the unit, perform well and are made in Yugoslavia, of all places! The problem of the play is that, at sometime, it must have seized to the shaft and rotated in the housing. The resultant wear of the alloy housing is hard to repair, and chances are that you will have damaged the bearing support spring to get it all apart. These springs are not available!

If the motor appears to have no side-play, remove the two long bolts and separate the shaft, end bell and armature from the housing. Note the presence of any spacer washers. Now clean out the housing and put a few drops of light oil in the bearing socket and set aside while you work on the armature.

With outside c-clip pliers, remove the clip from the shaft and ease the shaft out of the bearing. Again note the location of spacer washers. The brushes will drop off the commutator in this process. If an air hose is available, blow out the armature of any brush dust. Inspect the commutator and, if just dirty and not evidently badly scarred and worn, place the assembly in a drill press and gently polish it with #600 paper. Not too much, just enough to make it shiny again!

Back to the end bell. Note the condition of the brushes. Probably well worn down. So remove the three Phillips head screws and withdraw the plate. Clean the inside of the bell, light oil the inner surface of the bearing and lay aside. At this point, you will need Lucas’ replacement brush assembly. The one most commonly available is Lucas P/N WKB101 (54704696), BUT it is wired differently and uses three brushes. No problem, if you are handy with soldering iron and insulating materials. If you compare your original brushplate wiring with the new one, chances are that you will find that the blue and red wires go to the wrong brushes.

So, first of all, remove the third brush and its yellow lead completely. Cut the lead off your old unit, about 1 “from the pass-through molded grommet. Then attach (solder) this lead assembly to the new brush plate leads at the same location BUT with the colors reversed. Insulate the two joints properly. This maintains the necessary polarity and thus the direction of rotation.

Place the new brushplate in the endbell, same orientation as the original and attach with the new screws provided. Slip the assembly over the shaft (remember the washers). To get it to its right location, you will have to hold back the two brushes as the commutator passes them. Secure with washer and c-clip. Place some silicone sealer in the bell’s end groove. Now install the armature in the housing (washer) carefully. It will want to leap into position due to magnetic attraction. Helps to ensure that the housing and bell are aligned first. Both have indications in the outer lip. Install long bolts and nuts. Check for ease of rotation.

Make an electrical check now with suitable leads. The visible connector on the motor should be positive (red). Hold carefully - the unit tends to jump on start-up. Should run smoothly and direction of rotation should be anticlockwise when viewed from the shaft end. If all’s well, replace in the spider, attach the fan, reinstall on the shroud and hook-up the leads. You’re back in business.

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Contents copyright 2008, 2009 - Jody F. Kerr

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