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
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
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
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
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
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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