Troubleshooting the Starting
System
When the Starter doesn't engage or work at all
©
16-B
startingprobs.htm
NOTE:
It is very important that the reader of this has already read section 16-A!
To do that NOW: click on: 16-A
I also suggest reading the
Electrical Hints article
1. The very basic starting system is the
same on ALL Airheads; a starter motor, a starter motor solenoid,
a starter relay, the starter switch on the handlebars, a the
battery...and the necessary electrical wiring. There are
some variations in peripherals, including a special circuit in the
starter relay of the /5 series; and, some variations in the
circuitry which includes the clutch and neutral switches.
At its core, the Airhead starting system is very similar electrically,
with what has been in use on most cars and trucks for many decades.
2. The starter motor itself is a powerful
electrically operated motor. To obtain the type of
mechanical power needed from the starter motor (in some instances upwards of
1/2 to even one horsepower in mild temperatures and modest compression
engines, even more when the engine is quite cold and has thick
oil in it), the starter motor requires a quite high electrical current.
The starter motors in our Airheads are not very efficient motors, as
modern electrical motors go (the Valeo is more efficient than the
Bosch, however), so quite a lot of amperes might be
needed. Thus, there needs to be a means of controlling
these very
large amounts of current to the starting motor. A switch is
needed that will handle these large current flows. The heavy
duty starter solenoid switch, located ON the starter, is fed by a
large diameter copper-cored cable, directly from the battery.
There is NO FUSE. The
starter solenoid itself is activated by a modest current delivered by
contacts on the starter relay; via a BLACK wire that goes to the
SPADE terminal on the starter solenoid unit. The starter
relay is, therefore, a relay driving another much larger relay. The
sequence for starting is: Ignition key ON, which supplies
power to the START switch on the handlebars; pressing that switch
supplies power to the coil of the starter relay located under the
fuel tank. The starter relay contacts now close, sending a
quite modest amount of current to the solenoid switch located on
the starter motor. The solenoid switch is now activated and magnetically
pulls-in a large steel slug. One end of the steel slug has
insulated contacts which are pushed by the solenoid slug towards
large copper contacts and the pressure closes those contacts.
The large battery cable at the solenoid can now pass a very large flow
of electricity into the starter motor. In your Airhead, the
starter solenoid
is strictly a mechanically & electrically operated electrical
switch.
When the starter begins to spin up, a mechanical gear device called, generically, a 'Bendix' or Bendix drive, begins spinning. It is located on the rear of the starter motor on the starters shaft. This device, via spinning forces and guide grooves, moves rearward and as it moves to the rear it engages its teeth into the engine flywheel teeth, causing the engine to rotate. The teeth of the Bendix, and on the flywheel gear, are designed to enable quick meshing.
Later model airheads may have a Valeo starter motor which has permanent magnets instead of
field coils like the Bosch has, and the Valeo may also have a planetary reduction gear
inside its nose,
which allows the starter to develop higher rpm and hence higher
power. There is a factory bulletin on the starter relay on 1985 and
later bikes, information will be found the the Bosch-Valeo
article:
boschvaleostarter.htm
3. For the Nerdy: The internal
solenoid circuitry for the solenoid coil is slightly more
complicated than I have outlined, there are actually two coils,
one to pull in the solenoid, one to maintain it...but you don't
need the nitty-gritty of these details, and you wouldn't notice
unless you did a very careful inspection of the internal wiring
of the solenoid....or you were overhauling the solenoid switch
and failed to re-assemble it correctly.
4. The starter spins the Bendix
gear into the flywheel teeth as noted, and the engine is thusly rotated.
When the engine starts, the flywheel (clutch carrier on later
models) will then be rotating much faster
than the starter would be on
starter-only power. The Bendix is given reverse thrust by this action, helped
along in some by the teeth shape on flywheel (and Bendix), and the Bendix
now
disengages and moves back into the resting position (assuming you
are not still holding the starter button). A spring helps move the Bendix to home
(resting) position.
5. If the starter motor develops too much play in its bearings, it may
tend to bog down, and might even start to rub its armature against the
pole pieces. Worn brushes, grunge in general, worn
armature, and poor solenoid
contacts, are all other things that greatly reduce starter power output.
Earliest Valeo starters on the Airheads had a habit of the glue
letting go on the field magnets, jamming the starter internals.
Valeo replacement starters from such as
www.euromotoelectrics
are modified and don't seem to have these problems, or, are
greatly minimized. If you decide to install a Valeo,
in place of a Bosch, be sure the Valeo fits exactly properly.
See:
boschvaleostarter.htm
6.
It is a very good idea to
disconnect the battery before removing (or replacing) the
aluminum cover over the starter area. The reason for this is the potential (bad pun!) shorting
of the cover against the
battery terminal on the starter solenoid. That connection
wire needs proper orientation (to avoid shorts to the case/cover); and to be TIGHT;....things to check on before you
later re-install the
cover. You need only remove all the wires
at just the negative terminal of the battery to ensure the power
is disconnected. If you have ONLY the one large wire at the
negative terminal, you could disconnect at the speedometer cable
bolt instead. Yes, I do think it is acceptable to
modify the battery cable lug, so it will just barely push onto
the hollow speedometer cable bolt. Be SURE the TWO flat
washers are on that bolt.
7. If the starter does not work correctly, you need to
determine if the problem is in the starter motor, and/or its solenoid; or,
someplace else. Just what your bike's symptoms are, may well
determine your proper approach to your problem. If the
starter does not work at all, the tests may be a bit different.
8. It is vital that the battery be in good condition.
You can monitor its terminal voltage, and see what the terminal
voltage does during cranking attempts. If the starter is
very bad, perhaps drawing HUGE amounts of current, that can drag the
battery to under 11 volts. A formal load test on the battery is done in a
well-equipped shop; although Harbor Freight has decent testers
available at maybe $70 or so. Monitoring the voltage whilst you try cranking
the engine
(assuming the starter functions at all) might tell you quite a bit. If the
battery wires are poor, corroded, etc., the voltage at the battery during
cranking may be much higher than at the starter. Monitor the
voltage at the battery terminals itself too. Is the battery OK during cranking
attempts? A battery CAN have good terminal voltage at rest, and fall
dramatically, during cranking attempt (usually a failed inter-cell connection
causes this). You can also easily test for a bad +
cable or bad - cable.
9. If there is no tiny under tank click noise; then the starter relay, or
its sometimes troublesome socket connections, is suspect. A
meter or test lamp will easily reveal the problem. Monitor
the battery, and also trace the power into and out of that under
tank starter relay. The wires for the input and output power are RED
at the relay.
10. If that starter relay clicks but there is no major click/clunk from the
solenoid, then check the solenoid, be sure it is getting power to the
SMALL wire's terminal (this is is the small black wire) DURING cranking attempts. That
black wire is the power coming from, you hope, the starter relay.
11. No cranking? All seems OK? Remove (pull off) the black small wire at the solenoid. Run a
temporary jumper wire (any small gauge wire is OK) very
temporarily from that male spade terminal on the solenoid,
to the battery terminal next to it. If that causes
the starter to operate, where it would not before, then your problem is NOT in
the starter area; but more likely the thin black wire or the
starter relay; or push button. If the starter fails to operate, the starter or
solenoid is
at fault.
12. Certain years and models of BMW Airheads have various types of
interconnections with the neutral switch and the clutch lever switch at the
handlebars. These can introduce complications in your testing. You
may need to
find out if power is going through the starter relay. The easiest way to
begin this process is to leave the black small push-on wire DISconnected at the
starter. Key ON, Transmission in Neutral, pull in Clutch lever, emergency
shut off switch centered (ON position). Push starter button: is
there now power at the unfastened wire? If so, the primary problem is NOT in the starter relay.
I like to use an old headlight lamp for this test, saving the
ones with one burned-out section, as using this lamp draws about
the same current as the solenoid coil does, and is a better test
on the starter relay and its contacts.
13. Release the clutch lever; does it still have voltage?
If so, the problem not in clutch lever
switch.
14. Transmission to any gear but not in neutral. Clutch lever pulled back.
Starts? if so, problem not in transmission switch nor
clutch switch.
15. The /5, ONLY, had a peculiarity; and, the circuitry arrangement needs
understanding. The battery feeds power to the ignition switch, as in
all the airheads, but there was NO handlebars-mounted emergency cutoff switch. From the
ignition switch in the /5, the battery power fed a special starter relay that has had various
names, including Starter Lockout Relay. It is located furthest forward on
the left of the backbone under the fuel tank. This is not just a simple
relay, but it incorporates a simple transistor circuit; which, when stock, is
unfortunately overly-sensitive to temperature and to even slightly decreased battery
charge. When in the 'problem' area of cool temperatures
and/or
lower battery
charge, the relay may chatter, or sound like a cricket, and may even power the
starter solenoid that way too; making a much louder cricket or
clickety-clackety noise. To an old time mechanic, it sounds just
exactly like a near dead battery. The
transistor circuit purpose was to shut down possible starter relay operation (like in YOU
trying to start an already running engine!) as soon as the alternator
is spinning at engine idle or above. There are low battery and low temperature
problems with that starter relay circuit, and a modification is HIGHLY recommended, and there
is an article on this website specifically dealing with that problem, and the
fix.
The article is: slash5cricket.htm
Other than the added anti-start function, the
/5 starter relay coil is wired such that the grounding side of
its coil connects to the starter
pushbutton switch, from whence it is grounded when the pushbutton is pressed. If the starter relay
on the /5 fails to operate, it can be corroded inside, often fixable as it is in
a metal can that can be carefully UNcrimped and things cleaned-up inside. If
the transistor fails the relay will not usually work at all. The modification, which prevents problems at lower
temperatures, and/or slightly weak battery, is highly recommended.
There are NO complications in the /5, as to clutch switches, neutral switches in
the starter circuitry, etc.
16. After the /5, things started becoming more and more complicated in the starter
circuits. The only thing that was simplified was the deletion of the
/5 starter lockout relay, in favor of a more standard type of relay
(but, not absolutely a standard type). SOME of the later
starter relays contain one or two diodes...so be sure to read #19.
17. Change #1 came in the
early
/6. The neutral indicating lamp, which is green (and
the GEN lamp which is red) both went through a fuse, before
connection to the ignition switch. The starter relay coil in the 1974 /6 models was
wired to the same fuse as the INDICATOR lights...so if those lights are not
working, chances are the fuse is blown! That fusing did NOT
continue after the
early
/6.
The rest of the starter circuitry was the stone-simple starter
relay, and starter assembly.
18. The EARLY 1975 /6 models incorporated an emergency kill
switch....added between the ignition switch and the starter relay coil.
Sometimes these kill switches become corroded internally and act strangely
intermittent.
19. It was in the late 1975 /6 models, and then carried forward into
1977 and beyond (in some ways),
that the beginning of complications came about that drive some mechanics or
would-be mechanics crazy. BMW
added three things to complicate it all.
The starter
button, when pressed, no longer just grounded the starter relay negative side of
the coil to the frame. Whilst all the 5 speed transmissions, including the
early 1975 /6, had a neutral switch, the early models were NOT wired into the
starter section, like the later ones were.
Instead the path from that starter relay coil could take TWO directions:
A. If the neutral switch, located
on the transmission, was in the ON position, that grounded the coil, but through
a DIODE.
B. If the
bars clutch lever mounted
switch was closed by pulling in the clutch, the starter relay could be operated
from the starter button,
no matter if the transmission was in neutral OR
NOT. The diode was there to prevent the neutral lamp from indicating every
time the
clutch lever switch
was activated. These diodes have been known to
short circuit. If so, the neutral lamp will light up every time the
clutch
lever is used. If the diode failed OPEN, the neutral switch will
not allow starter operation UNLESS the clutch is pulled in. The
location
of this diode VARIES! For 1974-1980, except the R65, it
is UNDERneath the connection board in the headlight shell, where
it can't be
easily seen. For 1979-1980 R65, it is part of the wiring harness, near the
Voltage Regulator. For all the others from 1981,
it is INSIDE the starter relay!
THUS, the starter relay from 1981 is a SPECIAL relay; although an
aftermarket one can be subsituted,
and the diode added.
20. In 1978, BMW changed things again. This lasted into 1980. BMW
added 2 diodes...and a switch! These models had an under-fuel-tank brake
master cylinder. BMW incorporated a low brake fluid level switch, which,
when closed, turned on a brake failure RED light. The switch was wired to
that lamp, and via a diode to the starter relay coil. This modification
did NOT interfere with the starter operation, even if the diode failed in the
open condition. If, however, that diode shorted (HIGHLY unusual), and at
the same time one had a failed (closed) switch, or the level was low, the
starter could fire up, mysteriously, all by itself, and NOT release!...unless
the ignition or kill switch was used.
21. BMW
added a diode in the headlight relay. The location of that
relay varies with year and model. The wiring and operation
was such that during the time the starter motor was powered, the headlight
relay coil was NOT energized, which turned off the headlight.
Depending on model, whether USA or European, this varied
somewhat, and in most models...
the instruments and rear running lamp WERE left ON during cranking;
by use of the diode inside the headlight relay. Some had
various combinations. What is complicating the mess here, is that, at
least for USA models, the diode in the headlight relay was so connected that if
it SHORTED, then in some conditions of ignition switch setting, etc., it was
possible for the starter relay to fire up, and NOT be releasable, until the
battery was disconnected. Yes, the same
sort of thing like the 1978-1980 symptom of the shorted starter relay
diode. Thus the same SORT (nearly) fault could be had via a shorted
headlight relay diode or shorted starter relay diode!
Theoretically this problem could only happen in the PARK position of the
ignition switch. The fuse was
also now incorporated in the headlight relay section, and also fed the parking
light. Normally, if you used the starter button, even if the
fluid level was fine, the brake failure light would illuminate at every
start...this tested that lamp at each startup. It wasn't necessary to have
the fluid be low, then, to turn on that lamp.
22. With the 1981 models, no longer was there an
under-tank master cylinder, so the operation is slightly simplified. The wiring is exactly the same,
but withOUT the master cylinder switch and, of course, its
diode was eliminated. This lasted through the 1984 models.
23. There were several more variations and changes until the end of
production:
In 1985 and later, BMW put the starter button into the + power feed to the starter relay coil,
and the negative side of that starter relay coil went to the same diode and the
same neutral switch and clutch switch as before. By moving the
position of the starter button connection, BMW could incorporate the diode into the relay
housing. BMW also added another diode in the headlight relay area; this
time in series with its coil. The
starter worked the same, however. The GS and ST, and 1981-1985 R65 and R45 had slightly
different headlight relay contact arrangements; which in other models cut other
lights during starting besides the headlight lamp itself;...again, not a starter area to be
concerned with. [for the nerdy: the power for the instruments and tail light comes from
the ignition switch on these]. Earliest R65 models were different in this
regards.
11/29/2006: initial first draft and release
11/29/2006: correct typo editing error in h.
11/16/2007: re-number the items, combine certain sections.
Vastly improve clarity of descriptions.
10/03/2009: clarify a few things and clean up some
messiness.
11/22/2009: go over entire article, clarify certain things
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