Does not starts in gear

[cpazambrana]

Hi to everyone. I recently bought a1983 R80RT and I love the bike. However she only starts in neutral. I stall it the other day and unfortunately I then discovered that it will not start in gear, not even with the cluth pull in. I bought a clutch swith and tested continuity and is good. 1 turns to 0 when I pull the lever. I then went to the neutral switch. If I put it in neutral, there is no current flowing to the switch. If I engage a gear there is a full 12.6 - 12.7 volts. But if I pull the clutch lever it stays the same. Isn't it supossed to cut all current when the lever is pulled in like when in neutral? What else I should be looking for? I cleaned all the connections except for the neutral switch because the location is so difficult. Any help would be appreciated.

[gspd]

Is your neutral indicator light functioning normally?

You can easily access the neutral switch by removing the rear engine mounting stud and then prying or knocking out the spacer that it goes through.

[SteveD]

https://youtu.be/crfmG-nVdT4

https://youtu.be/3PRMVV7BJ8w

Consider the diode on the board in the headlight...seen in the second video..

[Seth]

On a '75 R90S that I caretake, the diode was bad, but because it allowed electricity to travel both ways, the neutral light would go on every time you pulled in the clutch. I replaced the diode with a 1N4004 diode. Make sure you install it in the right direction.

But based upon the second youtube video above, even if the diode is bad, the clutch switch should provide the a ground and allow the starter to spin, so I don't believe the diode is the issue. On the '75, and I believe the '83 as well, the clutch switch wires go into the headlight shell. One wire provides power in and the other goes to ground (brown). Verify you have a good ground, and that the other wire has good power. If you pull the ground wire off, verify you get 12v at that wire every time you pull the clutch and 0v when you release it. If you do, it's probably a ground problem. If you don't, then verify the power source the other wire is connected to in the fuse block.

This site has a lot more information...look about 1/3 of the way down the page.
https://bmwmotorcycletech.info/electricalhints.htm

And there's plenty of other pages on Snowbum's site for many other topics of interest. Highly worthwhile.
https://bmwmotorcycletech.info/electricalhints.htm

[gspd]

Sounds like a clutch switch circuit fault.
On some models the starter button powers the starter relay, and on others the starter button grounds the relay.
Need a wiring diagram specific to that bike to diagnose.

[Rob Frankham]

The starter relay (not the solenoid, the relay that is under the tank) takes it's current from the ignition switch via the kill switch. The positive side of the relay will always be at battery voltage when the ignition and kill switches are both on. Control of the relay is by the ground line. The ground side of the relay is connected to the starter button... if the starter button were connected direct to ground, the starter would work every time the button is pressed, even if the bike was in gear and the clutch wasn't pulled. This isn't 'healthy' because - a) engaging the starter against the resistance of a bike in gear isn't going to do the starter any favours and b) because it may result in the engine starting and the bike taking off when the rider isn't ready for it. BMW, therefore incorporated a system which prevents the starter from running unless a) - the bike is out of gear or b) the clutch is pulled. This is done as follows.

The ground side of the starter button is not connected direct to ground. It goes to a diode attached to the rear of the connection board in the headlamp shell. A diode is like a one way valve for electricity... current will flow through it one way but not the other. It then goes on to the clutch switch which is a 'pull to make' switch, that is to say that it carries current only when the clutch lever is pulled. With the clutch pulled, current can flow through the relay, the starter button and the clutch switch to ground which will
activate the starter.

The other end of the diode is connected to the neutral light switch which carries current to ground only when the gearbox is in neutral. When the gearbox is in neutral, current can flow through the relay, the starter button, the diode and the neutral switch to activate the starter.

The result of this circuit is that the starter can only engage when the gearbox is in neutral or when the clutch is pulled (or both of course).

The purpose of the diode is simply to stop the neutral indicator lamp lighting when the clutch is pulled.

Your symptoms imply that the connections as far as the diode in the headlamp shell are correct, that the diode is working and that connections to the neutral switch are OK (otherwise the bike wouldn't start in neutral). The assumption must be that the fault is in the circuit from the diode to groiund via the clutch switch.

I think you are saying that there is no voltage at the switch when the gearbox is in neutral. but that there is all of the time when the a gear is engaged. This suggests that the connection from the diode to the clutch switch is OK as there would be no voltage at all at that point if this connection were broken. That leaves the clutch switch itself and the wire from the clutch switch to ground. Since you say that you have replaced the clutch switch, the assumption has to be that the wire from the clutch switch to ground isn't connecting.

In short, therefore, you need to check the continuity of the Brown wire (with no tracer) from the clutch switch to ground.

At this point, my memory conflicts with the published wiring diagrams. The diagrams suggest that the wire goes direct to the main vehicle ground which is attached to the left coil mounting under the tank. My memory suggests that it actually goes to the ground connection in the headlamp shell. I may be wrong. In any case, I strongly believe that you will find the fault in that connection.

I attach a simplified wiring diagram of the starter circuit with the point that I expect to be at fault marked in red.

Clutch Interlock(1).jpg (77.74 KiB) Viewed 1371 times

I don't know how familiar you are with electric control circuits so I have given as much information as I can. This has led to a long and detailed post and, If I am telling you things you already know, I apologise in advance

Rob

NB for others reading this post, the circuit discribed does not apply to all airheads. In particular, the /5 series circuit is very different. Other model years may have detail differences.

R

[cpazambrana]

Guys I really appreciate all your responses. I will definitely check the ground that Rob refers to. Attached is a picture of the connection of the clutch switch. The two cables (brown and brown/yellow) goes into the harness from there. I will need to dismount the tank to trace them. I will keep you posted. Once I figure this out, the bike will be in like-new condition.

[gspd]

The assumption must be that the fault is in the circuit from the diode to groiund via the clutch switch.
In short, therefore, you need to check the continuity of the Brown wire (with no tracer) from the clutch switch to ground.

+1 , long post. I started to write pretty much the same thing but deleted it because I wasn't 100% sure of the wiring on that particular model. On some models, the starter switch gives power (instead of ground) to the starter relay. Either way, the starter relay needs a ground, either through the clutch switch or through the neutral switch.

Rob - We both suspect the issue is with the clutch switch ground however you highlighted the neutral switch ground in red.
If the wire you indicated in red was faulty, the bike would still start in gear with the clutch pulled in.

[cpazambrana]

The starter relay (not the solenoid, the relay that is under the tank) takes it's current from the ignition switch via the kill switch. The positive side of the relay will always be at battery voltage when the ignition and kill switches are both on. Control of the relay is by the ground line. The ground side of the relay is connected to the starter button... if the starter button were connected direct to ground, the starter would work every time the button is pressed, even if the bike was in gear and the clutch wasn't pulled. This isn't 'healthy' because - a) engaging the starter against the resistance of a bike in gear isn't going to do the starter any favours and b) because it may result in the engine starting and the bike taking off when the rider isn't ready for it. BMW, therefore incorporated a system which prevents the starter from running unless a) - the bike is out of gear or b) the clutch is pulled. This is done as follows.

The ground side of the starter button is not connected direct to ground. It goes to a diode attached to the rear of the connection board in the headlamp shell. A diode is like a one way valve for electricity... current will flow through it one way but not the other. It then goes on to the clutch switch which is a 'pull to make' switch, that is to say that it carries current only when the clutch lever is pulled. With the clutch pulled, current can flow through the relay, the starter button and the clutch switch to ground which will
activate the starter.

The other end of the diode is connected to the neutral light switch which carries current to ground only when the gearbox is in neutral. When the gearbox is in neutral, current can flow through the relay, the starter button, the diode and the neutral switch to activate the starter.

The result of this circuit is that the starter can only engage when the gearbox is in neutral or when the clutch is pulled (or both of course).

The purpose of the diode is simply to stop the neutral indicator lamp lighting when the clutch is pulled.

Your symptoms imply that the connections as far as the diode in the headlamp shell are correct, that the diode is working and that connections to the neutral switch are OK (otherwise the bike wouldn't start in neutral). The assumption must be that the fault is in the circuit from the diode to groiund via the clutch switch.

I think you are saying that there is no voltage at the switch when the gearbox is in neutral. but that there is all of the time when the a gear is engaged. This suggests that the connection from the diode to the clutch switch is OK as there would be no voltage at all at that point if this connection were broken. That leaves the clutch switch itself and the wire from the clutch switch to ground. Since you say that you have replaced the clutch switch, the assumption has to be that the wire from the clutch switch to ground isn't connecting.

In short, therefore, you need to check the continuity of the Brown wire (with no tracer) from the clutch switch to ground.

At this point, my memory conflicts with the published wiring diagrams. The diagrams suggest that the wire goes direct to the main vehicle ground which is attached to the left coil mounting under the tank. My memory suggests that it actually goes to the ground connection in the headlamp shell. I may be wrong. In any case, I strongly believe that you will find the fault in that connection.

I attach a simplified wiring diagram of the starter circuit with the point that I expect to be at fault marked in red.

Clutch Interlock(1).jpg

I don't know how familiar you are with electric control circuits so I have given as much information as I can. This has led to a long and detailed post and, If I am telling you things you already know, I apologise in advance

Rob

NB for others reading this post, the circuit discribed does not apply to all airheads. In particular, the /5 series circuit is very different. Other model years may have detail differences.

R

Thank you Rob. Of all of my motorcycle tasks I’m always challenged with the electronics which is my weak point. I always have to go back to the principles. I have solved 95% of all electrical problems on all the bikes that I’ve had by cleaning throughly all the connections and/or replacing cracked terminals. But it is always a pain for me the diagnosis process. That’s why I really appreciate that someone like you and others here is willing to take the time for such a detailed explanation.

[cpazambrana]

Is your neutral indicator light functioning normally?

You can easily access the neutral switch by removing the rear engine mounting stud and then prying or knocking out the spacer that it goes through.

Yes, the neutral light is functioning properly. I also need to remove the crossover of the mufflers to be able to work there.