Topic: Neutral Switch, how does it work?

[motorcycleclaude75]

Hey All,

I have a 72 CB500 Four and my neutral light constantly stays on.  I located the switch but can't find in the manual how it is supposed to work.

Could someone explain it to me. Pictures would be a bonus.

Thanks

[Klark Kent]

is your clutch cable properly adjusted?  is the dot on the cable arm lined up with the mark on the clutch cover?  does it engage the gears well and the light is still on, or is it telling you that you are not in gear when you let the clutch out all the way?  A broken swithc usually doesn't make contact even in neutral and the result is no light even when in neutral, so if your switch maintains contact all the time, I w ould check that you are actually in gear.  If you are then it is most likely the ground wire on your neutral switch has come loose, as they do sometimes,  but instead of no neutral light your wire is grounded to something, like the frame, and you have constant light.  The switch is in the sprocket cavity on the left side.  Wiser folks will come along and fill in anything i am probably leaving out.
good luck
-KK

[Bodi]

The switch has a rotating part keyed to the end of the shift drum. When the drum is at the neutral position the rotating bit makes contact with ground, completing the neutral light circuit.
Usually they fail by never turning the light on though. It's possible that a defect in the safety circuit is causing the lamp to stay on, I don't have a diagram fo the 72 bikes though.

[bryanj]

72 500 DOES NOT have a "safety Circuit"
What happens is the fibre "rotor" is held to the shift drum by a Phillips screw and located by a "peg" on the rear or the rotor in a slot on the shiftdrum.
In Neutral the brass piece on the rotor closes to the contact on the stationary part of the switch completing the ground path from the wire, via the stationary part then the rotor and screw to the shift drum and ground.

First test is disconnect the wire and if the light goes out you have a switch problem--if it stays on you have a wiring problem.

OK now the fix!
Rotors do show up occasionally at about $10 plus tax and shipping. I have several NOS that i will ship from the UK at $10 Including airmail if you need one.
Stators are rarely found and you will have to carefully inspect and repair it, Its held to the crankcase with one Phillips screw underneath all the cak (technical term) that builds up in there If you clean it off it should be obvious how it works If you still have difficulty please Email me direct and I will try and help you out.

[motorcycleclaude75]

I'll have take the switch apart.  The light is staying on when it's in gear or not.  I checked the connector, that's fine but cannot find the ground.

The switch (brass portion) looked bent but I don't know how it works, I need to take a closer look. It's difficult to troubleshoot because the side cover(including clutch) must be removed including the gearshift.  You can't change gears and see how it operates

Try Try again, I guess.  I'm tired of taking off that damn cover.

[andy750]

Would the fact that the wire to the neutral switch is cut make it a problem to actually start the bike? My neutral swtich wire has been cut in two (dont ask how) and I cant electric start my CB750K2. Starter isnt turning over. Anyone know?

thanks
Andy in Boston

[techy5025]

The neutral switch is rather interesting if you take it apart.  The phenolic part
that you see from the back can be unscrewed if you chip off the epoxy around the
edge.  The switch has a lot of oil in it so the epoxy is needed to keep the oil from
seeping through the phenolic threads.

What you will find is that the ball pushes a plunger that makes or breaks a ground contact
effected through the shell of the device to the engine case. Over time engine goop,
which contains metal shavings, gets in the part and causes a constant (but erratic)
ground which turns on the neutral light. The plunger has an insulated segment that
prevents contact when it is a certain distance into the shell.

Also the plunger changes shape over time (30 years?) and so the amount that the
ball has to be pressed to remove the ground changes.  DSS has the part and unless
your time is cheap....its probably best to get a new one.  You could try flushing the
part out through the ball hole while holding it down. 

I should have taken pictures of this doodad when I had it apart.    I wasted an evening
screwing with it.  Don't ask me how I know that oil WILL leak through the switch if it is
not sealed.

Jim

[bryanj]

techy are you talking about the 750 switch? cos the original question was about a 500 and they are totaly different.

[motorcycleclaude75]

Hey Guys,

Sometimes the answer in right in front of you.

Lately, I have all these questions because I just bougth a used engine and installed it.  I don't know the history of the engine other than the compression is good but I'm discovering little problems along the way.

As for the neutral switch, I discovered the end of the shaft is broken off  so the piece that is supposed to make contact is no longer there.  The brass piece of the switch was bent so it was making contact all the time hence the light was always on.

How I noticed this, I just compared the switch on the replacement engine to my original engine.  It was obvious my neutral switch will never work unless I replace the shaft.  Why didn't I think of comparing engines the first time 

Now I don't know how to replace the broken piece because the shaft is broken and there is nothing to grab on to.

I might have to live without a neutral switch for a while, but that's the least of my problems at the present time. 

[techy5025]

Yes...sorry....brain was disengaged.

Jim

[bryanj]

The shaft is part of the selector drum which means a complete engine strip to change, Is it worth it? or just rebuild the original and swop again

[KB02]

Yes...sorry....brain was disengaged.

Jim

That's okay. I have a 750 with the same problem, so it was good info for me. 

[TheSlug]

Ok, I had the same problem. The light was always on, and got brighter when in neutral. So I took apart my switch, cleaned it out, put it back together and now the light turns on when in gear... and turns off when in neutral. Any ideas? I'm pulling my hair out.

[Klark Kent]

model? year? it is a motorbike right?

sorry and welcome,
as you can see the switches are different on different bikes. let the inquiring minds know a little more about your particular scoot. 
-KK

[TheSlug]

Thanks for the welcome


It's a 1977 cb750.



EDIT:
Is there any reason that you can think of that the circuit would be completed when in gear... and broken when in neutral? I don't get it and I can't figure out how to reverse it. Seems like the gear box is depressing the switch when it shouldn't be.

[techy5025]

I would first check to see if the switch is firmly seated in its socket. If so,
I suspect that the internal metal part of the switch that determines whether
the light connection is grounded has been deformed. That was what happened
to the switch I took apart.....talking about a 750 switch here.

I am not an artist but attached is a pic of the disassembled switch with a
pictorial below. The red is the shell, blue the ball in front, black is the movable
plunger with the enclosed black spring, and green is the stationary contact that
connects with the wire by means of a screw.

The ball moves to the left when it settles into the detent in the shift drum at the
neutral position. In this position the "green" contact grounds the wire at the "yellow"
position of the movable plunger....at this position the plunger is not insulated and
the circuit is circuit is completed back through the spring to the case. When the ball
is depressed...not in neutral...the plunger moves to the right and the contact misses
the "yellow" area. In this position the plunger is insulated and the circuit is not
completed. Bottom line, the contact only grounds at one position....the yellow area.

Eventually, the coating that insulates the plunger wears away or the acid in the oil
etches it away and the contact makes contact at the wrong place turning on the
neutral light all the time. The other thing that can happen is the part of the plunger
that contacts the ball becomes distorted letting the plunger move too far to the left.
In this case the light will operate backwards, i.e. ground in all gears except neutral.

Not a very good design in my opinion, but hey they lasted over 30 years so .. 

If you decide to take one apart, you have to dig out all the epoxy around the phenolic
shell and then unscrew it...easier said than done.  I gave up and sprung for two new
ones from DSS.

Jim

[TheSlug]

Fantastic. Thanks for the explanation and pic. I know I can make this thing work... but I just put oil back in the motor, so I'll have to wait 'til next the change.

I wish I could find it for 10 or 15$ somewhere... it'd save me a little time, but the $30 on ebay is a bit steep. Although I'm finding that it's easy to spend $20 here and $50 there with these bikes... then before you know it you've spend 4x the total cost of the bike. 9 times out of 10 I'll fix a part before I'll buy a part... if I can.

Thanks a ton for the help.

[Derek B.]

Wow.  I think TheSlug just summed up SOHC4 ownership pretty neatly with the $20 here and $50 there bit.  I bought my bike for $200 seven years ago.  I'll never go back and analyze what I've spent on it since then.  I'd be pissed and it still isn't anywhere near where I want it to be!   

Also, I love the fact that we'll get someone who will take the time to draw up a multi-colored diagram of a switch that doesn't break all that regularly.  That's rad.  Sorry...I'm just having a personal moment there.