Starter Relay Open
Starter Relay Closed
This starter relay from an Airhead shows clear signs of corrosion and is indeed non-functional. In its resting state – that is, the starter button is not being pressed – its contacts are apart and no electricity flows through them. When the starter button gets pressed, electricity flows through the coil, turning it into a magnet. The magnet draws the upper arm down, making the contacts connect and flowing power from the battery to the starter.
BMW motorcycles have two different starter setups – one
for horizontally-opposed twins, and one for pretty much everything else. Horizontally-opposed twins have a starter with a built-in solenoid hanging right off the side of it—just like an automotive starter. Other bikes (F, G, K) have a two- piece setup; the starter is in one place, and the solenoid is in another place, probably under a body panel somewhere. These are a little easier to test, but only just a little. For the remainder of this article, let’s say your battery is put-
ting out 12.5 volts. With the bike’s ignition off, touch one lead from your DVOM to the positive terminal on the battery and the other lead to the lug on the starter. This test will only tell you if your starter is absolutely dead; if the DVOM readout is 12.5 volts, then you know you’ve got continuity from the bat- tery and through the starter to ground. If at this point the DVOM reads zero volts, there are a number of things that could be wrong, but it’s likely the problem lies within the starter itself. It could be as simple as corrosion between the starter chassis and the engine where it’s mounted, but it also could be that the brushes inside the starter have worn out. Either way and many ways in between, you likely need a new starter. Testing the solenoid (or starter relay) is a logical next step.
There should be two big lugs, and there may be some smaller ones or even a wiring connector. It’s the big, heavy-duty con- nection points you want to use for your testing. One will have a cable coming (more or less) from the battery; the other lug will have a cable going to the starter. The ignition solenoid is a type of relay, and it functions
much as relays do. At rest, there is no electrical connection between the contacts. When power is applied—in this case, by you pressing the starter button, which sends current to the “trigger” lug on the solenoid (one of the smaller wiring con- nections)—the contacts inside the solenoid come together, sending power from the battery to the starter.
60 BMW OWNERS NEWS August 2016 One of the things that can go wrong with the solenoid is that
the contacts simply degrade or corrode over time. They’re getting zapped with 12.5 volts several times a day, after all, and that can leave debris behind on the contacts, which can then get dirtier over time and stop making a solid connection. Testing the sole- noid is simple. You can use either the positive or negative termi- nal from your battery; it doesn’t matter which. Put one probe on a battery terminal and put the other probe on one of the solenoid lugs, noting the readout. Then touch the probe to the other lug on the solenoid and note that voltage as well. You should get one readout at zero and one at 12.5 volts (or
whatever your battery voltage is). If one of the readouts is any- thing other than zero or battery voltage, then it’s likely there’s a problem with your solenoid. If both solenoid lugs test the same, whether it’s at zero or 12.5 volts, the problem is likely the wiring between the battery and the solenoid, and that could include the connections at either end. You can also test from the solenoid to the starter. Put one
DVOM probe on the lug connecting the solenoid to the battery, and the other on the starter lug. If you get anything other than battery voltage (12.5V in the example here), then there’s a prob- lem between the solenoid and the starter. As a backup, test from the other lug on the solenoid to the starter – you should get zero volts. One of the frustrating aspects of chasing problems like this is
that everything can test out okay, but your bike still won’t start because there’s some minute problem inside the starter that looks fine when you’re using a DVOM, but fails when you actually put the full load of the battery to the starter. Clearances are tight, and if things are degraded even a little bit, it can prevent the starter from functioning properly. If you’ve seen anybody bang the starter on their car or truck with a hammer and the thing magi- cally starts after that, then you’ve experienced what can tempo- rarily “fix” a stuck solenoid. If you’ve seen somebody rock their
TECH
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134