Topic: Neutral Swith Issues

[Vintageguy]

1978 750F with neutral switch that is difficult to light up at times. Lately the light does not come on when actually in neutral, and difficult to find when stopped/engine running or not. Think I need a new switch. What do you all think? Thanks in advance. 

[CycleRanger]

The switch may be failing but more likely it's just gunked up. I would try removing it and cleaning it first.
Replacing the o-ring while you're there is a good idea but beware the switch can be a real bugger to push back in with a new o-ring.

[Don R]

 If you remove it, don't move the shifter while it's out, it locates the drum. 

[HondaMan]

Did you get it fixed up?
I often find them to be full of old oil gunk. If you soak it in, say, carb cleaner, it can weaken or dissolve the seal around the face of the phenolic base, which will let it then leak oil. You can re-seal it, or can get a new one from Honda (best) or places like PartsNmore or CB750Supply.

In the worst case: if the seal has broken/dissolved away you can unscrew the phenolic plug (gently, carefully) by making a smaller 2-pin or 4-pin (better) spanner to connect into the 4 holes on it: I have also used some long, thin needle-nose pliers before. Count the turns (make a mark across the plug and body) so you know how far back in to turn it: this is the Neutral Detent you 'feel' with your toe when shifting, and the number of turns inward sets that spring pressure. When it is apart you'll see how simple it is: clean the parts, add some sealant to the threads of the plug and screw it back in. The O-ring around it where it fits into the engine is 3x18mm size: e-mail me if you need one that you can't get locally, it is a common size.

This switch also fits a popular Honda inboard-outboard boat engine (Neutral Shifter indicator light), so Honda still supports it. If your Honda shop claims they can't get it, go to a Honda powersport boat motor dealer (marina) to get it: that's how I got some during the Covid nonsense. Same part, actually was $2 less!

[Scootch]

1970 750 K0 and I have a similar hard time finding neutral. I don't know the condition of the neutral switch but the light works when in neutral. It seems like it's a mechanical problem. What do I need to do to troubleshoot this?

[ekpent]

1970 750 K0 and I have a similar hard time finding neutral. I don't know the condition of the neutral switch but the light works when in neutral. It seems like it's a mechanical problem. What do I need to do to troubleshoot this?

On my 750's I just get used to snicking them up or down into neutral while the bike is still doing a very slow roll before I completely stop.Works well that way or if stopping try rocking it a little to get it in easier.

[HondaMan]

1970 750 K0 and I have a similar hard time finding neutral. I don't know the condition of the neutral switch but the light works when in neutral. It seems like it's a mechanical problem. What do I need to do to troubleshoot this?

Yeah, what Ekpent said: the dry-sump system in this particular bike, coupled with a wet clutch (but not quite as wet as in, say, the 500/550) combine to make a little more shaft-to-gear drag in this gearbox, That was the reason Honda modified this clutch some 6 times during the CB750's run, attempting to make it easier to find Neutral while ensuring a positive shift. The 1969-1972 (K thru K2 until 3/72) all share the original shifter drum design, and after that the shifter drum's "L" fork pattern in the drum grooves was widened to make the Neutral more positive to find. The tradeoff, though, means it takes more toe-torque to shift 1-2 and not accidentally END UP in Neutral: after that Honda softened the spring (by unscrewing the center plug) in the Neutral Switch  about 1/2 turn, which made things better. Drag racers covet the original shifter drum, though, because it shifts 1-2 faster and easier.

If your K0/1/2 has the free-floating ring on the clutch outer basket, make sure it hasn't become bent and stuck in place. It is supposed to float to help shake the top plate loose when clutching, to help encourage the other plates to loosen up. In the K0/K1 and early K2 bikes there may be only 6 friction plates when the engine received the thicker back plate, and there may or may not be 1 or 2 thin wires wrapped around a grooved inner hub at the back plates to hold those 1 or 2 steel plates snugly against the back of the hub, along with the loose ring at the outer end. These are rare (my K2 has the early K1 engine in it, apparently modified in production and re-routed around for some defect correction, ending up in the K2 assembly line later on), but I had one: now I have the more common 7-plate hub because I added oiling holes to the inner hub (used K3 hub, I think it is) and sipes to put more oil into the plates. This both cools the plates better and encourages the slip needed to find Neutral easier in traffic on hot days.

These sipes are shown in my book, if you have that thing.

[Scootch]

1970 750 K0 and I have a similar hard time finding neutral. I don't know the condition of the neutral switch but the light works when in neutral. It seems like it's a mechanical problem. What do I need to do to troubleshoot this?

On my 750's I just get used to snicking them up or down into neutral while the bike is still doing a very slow roll before I completely stop.Works well that way or if stopping try rocking it a little to get it in easier.

Thanks EK that's what I have been doing but it's still a royal pain trying to get it in neutral.  🤨

[Scootch]

Thank you for the explanation Mark. I do have your book but pretty much everything you said went over my head 🙂  I'll save it though and if and when I need it I'll refer to it. I'm a visual and hands on learner. I need to actually work with something to understand it. I'm just glad to know that my bike is "normal"  🥴

[HondaMan]

Thank you for the explanation Mark. I do have your book but pretty much everything you said went over my head 🙂  I'll save it though and if and when I need it I'll refer to it. I'm a visual and hands on learner. I need to actually work with something to understand it. I'm just glad to know that my bike is "normal"  🥴

If you ever have it apart: it was not unknown in the K0 sandcast era (while these bikes were being 'proven out' in 100 ways) for at least 1 shifter drum to get removed and the 'Neutral Divot' in the drum deepened a little, using a ball end mill. It worked, too. This tended to make the Neutral spot 'feel' stronger to his toe. I don't know HOW deep he went with it, however...