Topic: False Neutral

[The Gurg]

Trying to eliminate the false neutral I have on a shift into second. Occurs 10% of the time maybe. Usually if I’m forceful it won’t happen.

I bought new transmission bearings from Cycle X (Ken and the rest of the  Wisconsin guys are awesome!), and a new second gear. Also, replaced the broken clutch lifter plate with an OEM part.

Clutch plates and forks are within spec. I’ve read that usually the dogs or forks are the issues. Replacing second should address the dogs, I’m uploading pics of the forks. They don’t look bent to me, but I’m a newbie. The shift drum has a bend in the thin plate. Don’t think that could cause the issue, but maybe?

[TwoTired]

Might be helpfull to say what bike you are working on.

[The Gurg]

1975 CB750 K5 38k mi.

[MicahDT]

I will say, I rode modern bikes before I started riding my own vintage bikes.Vintage bikes seem to have harder and longer shifting motions. If its that intermittent, it may be your technique. I struggled with it for a while on my '76 CB750 and have missed once or twice on my '74 CB550. Just food for thought.

[The Gurg]

Yeah could be that I need to be a little more forceful. But happens more with one gear, so makes me wonder if it’s something that needs to be fixed. Anything else anyone can think of that I should check?

[jaytee-nz]

I find that chain tension can have an effect on the first to second gear shift - a loose chain will make it clunky, to use a very technical term !
That can lead to the odd false neutral.

[The Gurg]

Really, that surprises me. I hadn’t seen that anywhere. Are you talking cam chain tension? There’s no tensioner on the primary chains, right?

[flybox1]

There is a tensioner on the primary, but it is fixed and not adjustable.
Loose cam chain, tight cam chain...shouldnt make a difference on gear engagement unless the crank bearings are really, really shot.
Get a good non-synthetic MC oil.
Bel-Ray, Spectro...etc.

[jaytee-nz]

No not the cam chain - the main drive chain to the sprocket.

[HondaMan]

Take a real close look at the track for the "L" shift fork's dog (the dowel that moves it around). If the tip of the Neutral peak on that track is chipped or worn down, it can make the shift drag when it passes the Neutral and heads for 2nd. You can recognize the wear as being worn on the tip of the Neutral bump, but not down at the bottom of the groove.

Also, the L" fork will show wear on the sides of the fork where it rides in the groove of its gear, if it is bent or warped. What usually warps or bends them is: the bike falls over on the left side in such a way that the shifter gets hit and lifted, but not into gear, from Neutral. Most often, I used to call this the "car-hit-it-in-the-garage" accident, knocking the bike off its sidestand, and there was something on the floor near the shifter when the bike fell over...it happened a LOT in the day.

In the end, what happens is: the shift fork cannot push the C2 gear dogs all the way into the C5 gear's slots. Sometimes, the C5 slots may also be worn, which then tapers them and makes that gear tend to push the C2 back out while you are trying to push it in. Normally, those 2 gears should be replaced as a set, or at least the 2 of them recut together to have straight dogs and slot edges.

[evanphi]

No not the cam chain - the main drive chain to the sprocket.

And also if it is too tight! I found this myself when I first had my bike... 1-2 was very easy to miss with an over-tightened chain.

[PeWe]

The "false" neutral is between 4-5?
I have noticed that it is very easy to put 4 out of gear. Enough to nudge the pedal with the boot during acceleration.
Sometimes it will not gear in 5:th completely. But this is something I felt when gearing.

Better now with under cutted gears, 2-4. Now the other way, I have to release with clutch completely and shift gear more firmly, especially when gearing down.

[70CB750]

I like the Neutral between 4 and 5.  For long down hill coasting, it helps to cool the engine.

[robvangulik]

I've heard about it, never could find it, never missed it. Coasting downhill is a no go anyway in a flat country like mine

[HondaMan]

The "false" neutral is between 4-5?
I have noticed that it is very easy to put 4 out of gear. Enough to nudge the pedal with the boot during acceleration.
Sometimes it will not gear in 5:th completely. But this is something I felt when gearing.

Better now with under cutted gears, 2-4. Now the other way, I have to release with clutch completely and shift gear more firmly, especially when gearing down.

The next time you're in that bottom end, PeWe: put a 0.25mm - 0.50mm spacer washer on the side of the gear between it and the bearing (opposite end of the mainshaft from the clutch). That should make the 4-5 shift faster and more solid, but the neutral will go away.

I'd probably miss mine if I did that, though...

[PeWe]

The "false" neutral is between 4-5?
I have noticed that it is very easy to put 4 out of gear. Enough to nudge the pedal with the boot during acceleration.
Sometimes it will not gear in 5:th completely. But this is something I felt when gearing.

Better now with under cutted gears, 2-4. Now the other way, I have to release with clutch completely and shift gear more firmly, especially when gearing down.

The next time you're in that bottom end, PeWe: put a 0.25mm - 0.50mm spacer washer on the side of the gear between it and the bearing (opposite end of the mainshaft from the clutch). That should make the 4-5 shift faster and more solid, but the neutral will go away.

I'd probably miss mine if I did that, though...

I'll check that at next build. K1 extra engine I have, bottom.

[HondaMan]

The "false" neutral is between 4-5?
I have noticed that it is very easy to put 4 out of gear. Enough to nudge the pedal with the boot during acceleration.
Sometimes it will not gear in 5:th completely. But this is something I felt when gearing.

Better now with under cutted gears, 2-4. Now the other way, I have to release with clutch completely and shift gear more firmly, especially when gearing down.

The next time you're in that bottom end, PeWe: put a 0.25mm - 0.50mm spacer washer on the side of the gear between it and the bearing (opposite end of the mainshaft from the clutch). That should make the 4-5 shift faster and more solid, but the neutral will go away.

I'd probably miss mine if I did that, though...

I'll check that at next build. K1 extra engine I have, bottom.

If it is an "old factory" K1 it will not have the shim option, and few of the "New Factory" K1s had it, either. This method first showed up late in the K4 engines and is very common in the F0-F3 and K7/8 engines.

In the early engines, if the neutral between 4 and 5 becomes pretty common then the bushings inside those gears may be worn, letting them wobble a bit. The New Factory used cast iron, the Old Factory used bronze in these bushings. The bronze ones live MUCH longer and have fewer issues.

[PeWe]

The "false" neutral is between 4-5?
I have noticed that it is very easy to put 4 out of gear. Enough to nudge the pedal with the boot during acceleration.
Sometimes it will not gear in 5:th completely. But this is something I felt when gearing.

Better now with under cutted gears, 2-4. Now the other way, I have to release with clutch completely and shift gear more firmly, especially when gearing down.

The next time you're in that bottom end, PeWe: put a 0.25mm - 0.50mm spacer washer on the side of the gear between it and the bearing (opposite end of the mainshaft from the clutch). That should make the 4-5 shift faster and more solid, but the neutral will go away.

I'd probably miss mine if I did that, though...

I'll check that at next build. K1 extra engine I have, bottom.

If it is an "old factory" K1 it will not have the shim option, and few of the "New Factory" K1s had it, either. This method first showed up late in the K4 engines and is very common in the F0-F3 and K7/8 engines.

In the early engines, if the neutral between 4 and 5 becomes pretty common then the bushings inside those gears may be worn, letting them wobble a bit. The New Factory used cast iron, the Old Factory used bronze in these bushings. The bronze ones live MUCH longer and have fewer issues.

I'll might upgrade the gearbox with a K6 I have. I have not opened the engine yet, it might be in bad shape. The final axle will get double row bearing if cases allow it.

[dave500]

preload the shift,take up any slack first.

[The Gurg]

Here’s a few more photos of the shift drum. Hondaman thought that could be the issue. Got the 2nd gear in from CycleX with undercut dogs.

[The Gurg]

Still trying to diagnose this issue. Realized I misspoke before: I got a c5 gear from Cycle X not a c2.

1.) do I need to have c2 cut to receive the undercut dogs from Cycle Xs c5 gear. (I have photos attached of both the old and new c5.)

2.) should I have a machine shop fix the bent plate on the shift drum. Honda discontinued the shift drum, Yamiya carries it but it’s really pricey. I could order an oem plate from eBay, but the screw on the drum has the sides stamped down. Not sure how to remove the screw.

3.) anything else I should be looking/considering. The shift forks and everything else looks good to me, but I am an amateur mechanic. Would you guys reassemble once I address questions 1 & 2?

[The Gurg]

Oh and I wanted to point out the wear on my old c5’s dogs shown in the photo. Doesn’t look like much wear to me, but maybe that’s all it takes to make going into second hit or miss?

[PeWe]

Undercutting the gearbox. Send the entire transmission to a shop that do 2-4 with all machined dogs and opposite gear that also is cut.

The "neutral" between 4-5 was never an issue when aware of it and knowledge what to avoid, how to shift to 5:th gear to make sure it is completely in.
2 and 4, the CB750 std out of gear sliders.

[ofreen]

preload the shift,take up any slack first.

Yep

[spotty]

on a related but not at all honda issue, on the yamaha vmax you have rubber engine mounts ( to cut down vibration) and the engine can twist up to an inch in these under hard acceleration, this is enough to put the gear change far enough away from your foot ( which being on the rigidly mounted footpeg ) that under aforementioned hard acceleration you would only nudge the gear change instead of giving it the proper lift it needs.

fitting solid engine mounts has fixed that problem, now my hands go numb from the vibration within about half an hour..... 

[HondaMan]

Still trying to diagnose this issue. Realized I misspoke before: I got a c5 gear from Cycle X not a c2.

1.) do I need to have c2 cut to receive the undercut dogs from Cycle Xs c5 gear. (I have photos attached of both the old and new c5.)

2.) should I have a machine shop fix the bent plate on the shift drum. Honda discontinued the shift drum, Yamiya carries it but it’s really pricey. I could order an oem plate from eBay, but the screw on the drum has the sides stamped down. Not sure how to remove the screw.

3.) anything else I should be looking/considering. The shift forks and everything else looks good to me, but I am an amateur mechanic. Would you guys reassemble once I address questions 1 & 2?

How about if you PM me your mailing address? There looks to be a chip on the Neutral bump on the shift drum, probably caused when it jammed and bent the pin flange. I have drums: what is the serial number of the crankcases?

[The Gurg]

So here’s where I’m at:

I’m thinking that the undercut c5 dogs and c2 slots from Cycle X will fix the issue. And that the broken clutch lifter plate was a big contributor (which I’ll replace).

No one seems to think the shift drum plate being bent is an issue. I’m still struggling to understand the exact mechanical purpose of the plate. Would love some insight. I have a machine shop straightening the plate. But the shop is going to try to do it without removing the screw or plate. Makes me question what the integrity of the piece will be after bending back. So, I also ordered used SOHC 1975 CB750 (should be an exact match) shift drum and forks from ebay for $40. Should I use the machine shop unbent drum or the used eBay drum?

Also, planning on doing a dry run (with some assembly lube) of the transmission. Peter Anderson has a pretty cool trick on how to do that.

Go to the 34 minute and 52 second mark:

[HondaMan]

Here’s a few more photos of the shift drum. Hondaman thought that could be the issue. Got the 2nd gear in from CycleX with undercut dogs.

The Neutral Bump looks to be OK, but the bent alignment flange, not so much. This will tend to bind and drag the rotation when it comes up against the spring detent wheel, making the shift action stall out and miss the full shift. This essentially holds it in-between the gears when that happens. The "crisp" shift these bikes are known for was due to a combination of the dry sump, the large gears and loose dog tolerances, so there is a lively difference between them when they negotiate the final dog-in-slot move, making the clunk we all know so well. This also makes the wear marks you see, and since 1-2 happens a LOT in this bike, they wear the most for it.

The wider Neutral detent yours has indicates it is a late K3 or later type "improved" shift drum. These have a little slower 1-2 shift but a more easily-found Neutral on a hot day, as it holds the fork's dog in-between the gears a little bit longer in travel.

[The Gurg]

Is this the neutral bump on the L track?

[PeWe]

Neutral switch will extract into this hole (dimple) and lit the green pilot indicator lamp.
See yellow arrows to the right.