Series Diesel starter motor rebuilding

by Adrian Redmond

There have been a few postings on the subject of series diesel starter motors of late, and having renovated one of mine today, I thought I'd add my pennyworth...

First a definition of terms to minimize confusion. A Dyer gear is the gear on the Land Rover starter motor that goes inwards to engage the flywheel when the starter motor is spun. It is like a bendex gear except that it does in the opposite direction. A bendix is forced outwards when it is spun.

Let me start by putting this starter-motor thing in perspective. I have three series vehicles plus a couple of spare starter motors. All units have given trouble from time to time (usually when its raining or snowing and the truck is most unpleasant to work on) but I have never yet seen a starter motor failure which could not be rectified by a simple rebuild and cleaning. I have, so far, never had to replace any parts, and all my 5 starter motors are of 70's vintage.

The most common failure is the deathly click, where the starter solenoid clicks but the motor doesn't turn. This can be due to 2 common fault scenarios - 1. the solenoid isn't being drawn back enough to close the high current switch and send power to the motor (usually due to a wet or dirty switch, low power due to bad earthing, or a crudded sticking solenoid piston) or 2. the motor is stuck with the Dyer gear engaged in the flywheel, and has not the momentum to turn the flywheel (usually due to dried grease on the Dyer/armature spindle or bad earthing.) How the Dyer gear gets stuck defies my imagination, although I have seen this on many lighter-duty starters. Ford and Massey Ferguson used to have a small square end on the armature spindle which could be hit with a hammer or turned with a key to disengage. Otherwise rocking the vehicle back and forth in gear sometimes helps.

If the starter clicks but does not engage, and if the lights do not dim whilst you hold the ignition key in start position (dimming indicates heavy load, a hint that the starter motor might be turning against an immovable object = Dyer gear stuck against flywheel), then I'd suspect the solenoid.

To start the vehicle and move it to a handier place (like home), you can short the two terminals on the solenoid with an insulated screwdriver. This should start the motor. But don't rely on this method for weeks, the chances are that something is wrong and it will get worse.

Solving this problem can, at a pinch, be accomplished by just removing the solenoid, but if the solenoid is dirty and caked with crud, assume the rest of the starter motor also needs attention. Take a day off and pull the entire works out and onto the bench. Contrary to rumors on this list, the starter motor can be removed and refitted from below, but depending on the condition of your engine mounts (which determine the relationship between the lower sump flange and the inside of the long chassis member) it might be a tight fit. With practice it can be done, and it is better than having to dismantle the manifold.

Once you have the unit on the bench, the procedure is as follows -

Undo the two #10 nuts which hold the solenoid onto the assembly. Undo the copper link (or cable) between the solenoid and starter motor (#14 on the motor #13 on the solenoid). Remove solenoid carefully. This will reveal the solenoid plunger (piston) which is still fixed to the rest of the unit, surrounded by a spring which should follow the solenoid unit. Note that you have two rubber washers which seal the solenoid mount shafts - these might need replacing.

Clean the mating face of the solenoid with a wire brush (there may have once been a paper gasket here) I recommend cleaning the solenoid outer and painting it black. Clean the terminals with a wire brush. Clean the inside of the solenoid with WD40, then spray alcohol or contact cleaner into the solenoid to clean the switch. The two phillips screws which seem to hold the bakelite unit onto the coil may be removed, but the unit will not come off the switch as it is soldered on - so leave the screws alone. Blow out the solenoid using compressed air, dry with a tissue. When you are sure that the cylinder is clean and dry, give the inside surface a light coating of graphite powder.

By connecting a multimeter to the terminals and pressing the plunger at the base of the cylinder, you can check the switch contacts. They are normally open, and when closed should give virtually no resistance.

Now is a good time to lightly sand the outside of the solenoid and paint it, it should dry whilst the rest of the work is in progress.

Place the starter motor upright in a wide jawed vice, with the Dyer pointing downwards. Avoid overtightening the jaws.

Undo the two nuts and one bolt (#11 or 1/4" UNF) which hold the cover on. The two bolts are the ideal position for connecting the earth strap between the motor and chassis later on. (I prefer this connection point to the bottom flange of the sump housing, as it necessitates removing the strap and thus making removal of the starter motor easier. It is, IMHO, a better earth connection to the main unit on the engine which needs a good earth.

Remove the die-cast aluminum cover off the starter motor. Be careful not to damage the rubber seal which is inside this cover. Remove and wash the seal. Check the cover for damage - often the standard LR braided earth strap has vibrated against the cover, wearing a small hole which allows rainwater to enter the starter motor. This can be filled with Plastic padding or similar. Clean the cover and put it aside.

Removing the cover will have revealed the starter motor end plate, on the inside of which are the four copper brushes. (2 to the stator coil and two to the cover plate) Undo the two long (#11) bolts which hold the end plate on. Use low torque to loosen these as they can snap. They are long, running through the stator right down to the casting at the other end. When removed, they should be cleaned with a wire brush, and tipped with copper grease to ensure easier removal next time - which should be in around at least 5 years.

Then lift the plate - slowly, as the copper brushes must disengage the rotor. When you have this off enough to get access to the inside, use a long nose pliers to hold back the spiral springs which retain the two copper brushes which are attached via short tails to the stator housing. This will free the cover plate.

Notice that the copper brushes may be worn at an angle - due to the eccentricity of the spring which holds them against the rotor. If this is the case, notice how they are worn, and be sure to insert them to opposite way when rebuilding, to get the longest life out of the brushes. I suppose one could replace them, but I have never needed to. I don't even know if they can be bought loose. Thoroughly clean the cover plate and brushes. Note that there is a plastic bearing on the inside of the cover plate which has two slots at 180 degrees from each other, these align with the pin through the rotor axle when reassembling.

Next, remove the stator housing (the metal tube which comprises the majority of the starter body. This is only held in place by the two long bolts which you have removed. So it should come loose with a little help. Notice that there is a thin rubber seal around the bottom, so don't pull too hard or the seal might be damaged. The stator housing, which includes 4 coils and four iron cores is a complete unit. The cores are held in place by 4 large Phillips screws. So far I have never managed to undo these to enable me to remove the cores and coils and clean the unit the easy way. I guess it may be possible, but I have ruined enough screwdrivers and impact drivers trying so I have given up on this step. Just blow the crud out of the coils, clean the cores with WD40 and contact cleaner/alcohol/thinners, pack the inside with plastic bags or tissue paper, and clean the outside with a wire brush or sandpaper. Clean with thinners, dry and paint black.

Before attempting to remove the rotor, you must first remove the pinion which holds the solenoid actuator in place. This has a large #18 locking bolt. Clean the head of the pinion, you will notice that it has a finely engraved datum arrow which points towards a similar arrow on the casting. The pinion is eccentric, allowing to joggle the fulcrum to remove the yoke lever inside. Aligning the arrows ensures that the yoke lever is aligned properly with both the Dyer gear and the solenoid piston. Undo and remove the pinion, then pull the piston out of the yoke. Before removing the yoke (which will fall out when you lift the rotor assembly free, mark the yoke with a marker pen, so that you can be sure to reassemble it in the correct position.

Now you can lift the rotor out. The plate between the rotor and the casting is held in place by a small pin on the inside, so a small amount of leverage with a small screwdriver may be needed. The rotor and its shaft, complete with end plate and Dyer gear. This should also free the solenoid actuator yoke, and leave the empty casting. You will also have a small rubber block which seals the gap between the solenoid and the stator housing. Clean this in WD40 and hot water. It should expand again to ensure a tight fit when reassembling.

Clean the rotor carefully (Although I must admit to using a delicate pressure against a brass wire cup in the bench drill!) Use WD40 to clean the shaft, bearings, Dyer gear and end plate. Use compressed air to remove all crud and WD40. Lubricate when clean with WD40. Make sure that there is no deposits or calcification on the electrical parts. Check that the Dyer gears are now worn (though they should be flanged on the face which mates with the flywheel - this is design NOT wear!)

Clean the yoke and ensure that it is not worn or chaffed. Clean the solenoid plunger - which is copper - with WD40 and then alcohol. It is this part , together with the solenoid cylinder, which when covered in crud and grease is the most common cause of malfunctioning starter motors. Coat the piston lightly with graphite powder. A word on the use of powdered graphite. If you use to much, the surplus powder will soak moisture and grease to itself, and become the next layer of crust to be removed in a few months. Use small amounts, just enough to fill the small cracks in the surface of the copper with graphite to aid easy-running - no more. Blow surplus graphite away with a air gun. Clean the casting (the bit which is left in the vice when everything else is removed). This may be full of grease and crud. This part protrudes into the flywheel housing, and any oil/grease in here will eventually get into the starter motor. This part is a perfect example of the need to ensure that you never use more lubricant than necessary.

You should now have all parts clean, dry, repainted, and ready for reassembly. Rebuilding, as they say in the LR manual, is the reverse of disassembly. Take time, make sure everything is clean, and all mating surfaces are dry and sealed. I use liquid gasket to seal the joint between the solenoid and the casting. This is probably the most moisture and corrosion vulnerable part of the entire assembly so a good seal is important.

When you have reassembled the entire unit, mount it in a vice and prepare to test it. You will need a good 12 volt battery (you need amps for this so don't fry your 12 volt bench supply - use a battery) and a set of jumper cables. Connect on end of the cables to the battery, and the negative at the other end to the threaded stud which protrudes from the starter motor cover. Now touch the positive cable to the solenoid actuator terminal (the thin spade terminal) this should draw the solenoid back and shunt the Dyer gear forward. Now touch the positive cable to the large terminal on the side of the starter motor (the one with the copper strap or wire connecting it to the solenoid) the motor should fly into action, this time it's centrifugal force which throws the Dyer gear forward. Check that the Dyer gear has enough WD40 lubricant or fine (sewing machine or 3-in-1 oil) to move freely. Finally, touch the positive cable to the "input" terminal of the solenoid (the terminal where the thick battery cable connects on the vehicle) AND to the solenoid actuator spade terminal at the same time, this should close the solenoid and actuate the switch which allows power to flow to the start motor. The starter motor should work. If you have done everything methodically - it will - otherwise suspect the brushes or stator coil - though I must underline again, that I have not seen these fail yet.

The fun bit is refitting the unit onto the engine - from underneath. Much easier if you have a friend to lean in from above and help you. Remember the trick with the jack below the sump to aid movement. Maybe a crowbar at the left engine mount to "ease" the engine to the right if necessary.

Reconnect all cables, maybe even a dab of Vaseline over the connections to resist corrosion. Make sure your earth connection between the chassis (I use the angle iron which stiffens the outrigger to the main chassis by the footwell for this). It can never be stated enough that bad earthing is the most common cause of bad starting. If you rely on the earth from the battery to the chassis, then the engine only gets its earth via the wiring loom and the springs - and of course the coolant. Bad earthing of the engine is also a contributory factor to corrosion problems, as it establishes a potential difference between the chassis and the engine.

Your new starter should work for a few years without problems. I keep a couple on the bench, along with a generator or two, an axle or two, and the odd radiator. Then it's easy to be up and running and the repair can be undertaken at will. This is a typical Land Rover maintenance project, one which usually does not require spare parts, but which underlines the need for keeping this free of dirt and lubricants. The entire job can be undertaken in under 4 hours, though an overnight is preferable if you want to repaint the starter motor parts. I hope this little missive helps someone else some rainy day... Roverly regards, Adrian Redmon

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