Topic: CB500 four k1 - 3rd gear issue

[roque75]

Hi everyone!

I need some help to identify this 3rd gear issue, so I can fix it.

So, this is happening only in the 3rd gear! It’s starts to rev for a second and then it gears again for itself. And there’s a loop of this while I’m in 3rd gear…

If not a false neutral because i don’t need to shift it again.
And it happens every time it’s in 3rd gear…
It doesn’t matter the speed nor rpm!

Thank you for your help!!
Cheers
 

[bryanj]

Selector worn or gear dogs rounded, either way its engine out and stripdown

[roque75]

Thank you bryanj!

Yes, I will need to take the engine out.

But if I’m 100% sure that it’s the either the gear dogs or the selector, I will know what I need to search.

Can it be anything else?

[roque75]

Don’t you think that if the issue is from the selector, it will be happening with more gears?
This only occurs in 3rd gear

[bryanj]

Nothing else unless it is from the first 6 months of production and not modified.
There are three selectors in there and the centre one is a known weak spot, also nla from honda but a european firm was cbc manufacturing them at a cost of about 200 gbp.
As to the gears it wont be the 3rd gear set worn as you move a different gear to engage 3rd, you will have to strip and inspect, sorry there is just no other way.
Engine out
Generator off
Points cover and plate off
Clutch cover off
Strip out all inside clutch cover including primary shaft
Starter out
Remove all casing bolts and split casing making sure you know exactly which shells fit where

[HondaMan]

Bryan:
Isn't this the one that comes from the middle shift fork being worn on its tines? We used to call it "burned tines" back when, because they would be blue from the heat.

[bryanj]

Could well be Mark but when its been doing that for some time the dogs and mating holes get rounded.
That centre selector came from the 350 twin i think, along with the selector drum and is now very difficult to find.
If you look up Oddjob and ask him he knew of an Italian (i think) firm doing expensive cnc parts

[HondaMan]

Could well be Mark but when its been doing that for some time the dogs and mating holes get rounded.
That centre selector came from the 350 twin i think, along with the selector drum and is now very difficult to find.
If you look up Oddjob and ask him he knew of an Italian (i think) firm doing expensive cnc parts

I suspect you're right about the 350 drum part: I THOUGHT it looked real familiar the first time I saw one. That -286- partnumber is a tipoff, too. It was used in the old Hawk series bikes and the 350 twins, both. I always thought Honda just nabbed the long-tried shifter drum and made new forks, or modified those old versions.

[Deltarider]

Could any of you guys give the full partnumber?

[bryanj]

Not off hand just centre selector on the drum

[reddyvv]

It is a CB and CL350 part number

24212-286-030

A couple of used ones on ebay and a pricey new one

https://www.ebay.com/itm/364154550727?

[HondaMan]

It is a CB and CL350 part number

24212-286-030

A couple of used ones on ebay and a pricey new one

https://www.ebay.com/itm/364154550727?

That's the one for the 350's center fork: I don't have a solid reference on whether the 350's middle shift fork is long (or shortened) enough to fit the 500, though. I think the tines are a slight bit shorter in the 500.

At CMSNL they list that as the same one for the 500, though: I seem to remember something about a Honda Shop Note (similar to those used on the early 750s) about the center fork, but can't remember what it was: my shop(s) never encountered the issue.

[reddyvv]

Are you sure?

According to Partzilla 24212-286-030 is FORK B, GEARSHIFT.
The drum is listed as 24301-286-050

[HondaMan]

Are you sure?

According to Partzilla 24212-286-030 is FORK B, GEARSHIFT.
The drum is listed as 24301-286-050

You're right: I had 2 partnumbers and thoughts going above and deleted the wrong one.
So I rewrote what I meant to say. 

I seem to remember that the early 500 had a different middle shift fork that was changed early on to the one everyone knows now. It was somehow 'errant' and it would burn the shift fork tines.

[roque75]

you will have to strip and inspect, sorry there is just no other way.
Engine out
Generator off
Points cover and plate off
Clutch cover off
Strip out all inside clutch cover including primary shaft
Starter out
Remove all casing bolts and split casing making sure you know exactly which shells fit where

Done!

All gears out and inspected. The 3rd gear mechanism (gear dogs and fork) indeed have some wear as you can see in photos…

However I measure it and it looks it still in the specs.
I also force it to rotate and it doesn’t seems to slip….
Force doesn’t look bent.

Do you think that this is the issue for sure? Or do I still need to look for something else?

Thanks

[Pbeattie89]

I would say you need a new set of gears and a fork. The dogs are rounded. It doesn't take much. You can also see the wear mark in the middle of the "C" section of the fork that is caused by dogs slipping out and pushing the gear hard into the fork. The pads at the tips of the fork are also worn from the looks of things. My 1983 cr250 did the same thing the exact same thing.

Sent from my SM-G991W using Tapatalk

[HondaMan]

This wear on the inside bend of the fork looks like every other CB500 I've ever taken apart(!). I file/grind off the flares on the sides of the forks and then test the shifting and gearbox functions for full engagement of the dogs in their slots: they should engage no less than 3mm depth. It's pretty rare for the tips of the forks to be worn down such that they won't shift the wobbly gears.

This issue in the CB500 tranny often comes from using too-light oils and/or waiting too long to change it. For example, when I had my shop it seemed like every single 500 owner who came in could not remember the last time the oil was changed, as in, "I got the bike last Spring and didn't change it before winter. This is the first oil change since last year" - and the speedos showed 3000-5000 miles on them. Changing the oil then showed up shiny grit, which I learned later came from these gears-and-fork contacts. I took care of something like 10 of those first- and second-year 500s for those kids, and they were universally the same. They often rode together, too. Tearing one down for a parking-block-pushed-the-oil-filter-thru-the-cases incident showed the center fork looking just like yours: new cases later, the bike worked fine. The last 2 CB500 engines I've had for rebuild here have both looked like yours, too.

In the end, if the gears have not become so wobbly on their shafts that they disengage themselves (manifested as jumping out of 2nd or 3rd gear) they will usually work well enough to ride in normal service. There's several guys out there who will back-cut the dogs for you: that works, too, but will require you be more deliberate with the shift. The 500 would literally let you shift sans clutch once the engine warmed up, with good oils: mine did it without complaint using Castrol XLR 20w50, acting as if the clutch was merely a stop-and-go device.

Worn gear dogs are always a worry: if they are rounded so much that they engage only the rounded portion into the slot of the adjacent gear, then they can push each other apart under load. This causes the jumps-out-of-gear troubles we see once in a while on the 750 (2nd gear, especially). In that case, back-cutting the dogs will straighten things out quite well.

[bryanj]

That selector is toast, but its unusual in that it is an outside one. What does the centre one look like?

[roque75]

Center one is like new.
Right has just a bit of wear, nothing bad like the left one.

So, can I just replace this gear and fork and expect my problem is fixed?
Won’t it start to wear the new gear too?

Should I also replace the 3rd gear since the dogs wear it a bit? It doesn’t look too bad to me.

Should I look for something else or maybe the root cause?

Thanks!

[bryanj]

The last pic that gear needs new, you can see the wearmarks between the slots where the dogs have been dragging.
Plus the gear with the dogs that mates with it and the selector that moves it as it is probably bent.

BE CARFULL with what you get/fit as one of the gears was modified during the run of the 500 and needs the gear on the other shaft that runs with it as it was the profile of the teeth that altered

[Pbeattie89]

The last pic that gear needs new, you can see the wearmarks between the slots where the dogs have been dragging.
Plus the gear with the dogs that mates with it and the selector that moves it as it is probably bent.

BE CARFULL with what you get/fit as one of the gears was modified during the run of the 500 and needs the gear on the other shaft that runs with it as it was the profile of the teeth that altered

Yes, be very careful. I would suggest looking for a complete gear. Set on eBay would be the easiest way. Or you could get the gears repaired and get them undercut.
But you would still need a new selector fork

Sent from my SM-G991W using Tapatalk

[roque75]

BE CARFULL with what you get/fit as one of the gears was modified during the run of the 500 and needs the gear on the other shaft that runs with it as it was the profile of the teeth that altered

Thank you! I didn’t know that…
Are the teeth profile visually noticeable?

New profile won’t fit, right?

[bryanj]

Visually no but shafts will not "mate" or turn

[dave500]

also check the shift drum sideways movement,this was improved on the 550s with a different locating mechanism,if the drum can move sideways it takes the fork with it,heres one i prepared earlier!

[bryanj]

The 550 is a completely different shifting mechanism and whilst i have seen a few 550 gears shear dogs like in the last pic i have not seen it on a 500.
If you can find a dealer who still has the old microfiche "supercision" list the one 500 gear part number goes to i think a 550 and turns up as a 2 gear "set" with the different tooth profile.

[HondaMan]

also check the shift drum sideways movement,this was improved on the 550s with a different locating mechanism,if the drum can move sideways it takes the fork with it,heres one i prepared earlier!

Hey, Dave: is that one of those new lightweight dragracer gears?

[dave500]

sure is Mark,its the 11,000 rpm test!

[bryanj]

Aah the crunch testing result

[dave500]

that was few years ago,popped out of third couple times under load on a long ride,made it home with no 3rd,found the three lugs in the bottom of the pan,couldve been way worse result?

[HondaMan]

that was few years ago,popped out of third couple times under load on a long ride,made it home with no 3rd,found the three lugs in the bottom of the pan,couldve been way worse result?

Boy, that was LUCKY!
A 750 I once fixed broke off one of the C5 dogs and it flipped up on top of the whole shaft, then right in between the gears. Made a nasty mess.

[dave500]

yeah i escaped a long skid rear wheel lock up or two shafts being pryed apart splitting the case where its never been split before?

[bryanj]

Dave, you were lucky. Thats one of those things i have heard of but never seen in person, loads of knackered centre selectors though

[dave500]

this was actually a 550 motor!

[bryanj]

For some reson the 550 sheds dogs way more than the 500

[Oddjob]

The right hand selector is toast I'm afraid, it's also hard to find and bloody expensive when you do find one. 24211-323-000 BTW.

There is a witness mark on the left hand selector as well, not a big one but sometimes not right in the gearbox when they occur. 24213-323-000 You may want to consider changing that as well.

Oddly, the centre selector isn't that bad, it's normally that one which wears away faster than the others. As explained it's a CL350 part number, I do happen to have 2 NOS ones, I also have a NOS left hand selector but not a right, never found one going cheap enough to tempt me.

I also have a complete NOS gearbox, every gear, thrust washer, circlip, bearings and shafts, been collecting these for some years and finally found the last gear I was missing last year, not sure yet if I'll fit it in my restoration this year but may not if the old box still looks ok.

One of the pics shows mainshaft 2nd and 3rd gear, it's the one where the middle selector is fitted to it, what's concerning about that pic is the engagement slots on mainshaft 4th gear, that's the one right next to the fixed gear on the mainshaft, so closest to the clutch, the slot looks shiny, like something is wrong, there's also what looks to be a small sliver of metal sticking to the gear. I'd check that if I was you.

Has the box been apart before? might be that someone assembled it wrong, it's easy to orientate some of the thrust washer wrong and the circlips are meant to be fitted a certain way as well.

As Bryan says, there is a firm in Italy making really fantastic copies of the selectors, they are better made, have harder tips so should last longer and the finish on the surface of the selectors in just ace. Not cheap though, I bought all 3 in 2022 and the cost then was 150 euros for each selector, 300 for 2 but an offer of 400 euros for all 3 plus postage.

Pic of the middle selector compared to a NOS Honda one.



You need any details PM me.

[HondaMan]

The right hand selector is toast I'm afraid, it's also hard to find and bloody expensive when you do find one. 24211-323-000 BTW.

There is a witness mark on the left hand selector as well, not a big one but sometimes not right in the gearbox when they occur. 24213-323-000 You may want to consider changing that as well.

Oddly, the centre selector isn't that bad, it's normally that one which wears away faster than the others. As explained it's a CL350 part number, I do happen to have 2 NOS ones, I also have a NOS left hand selector but not a right, never found one going cheap enough to tempt me.

I also have a complete NOS gearbox, every gear, thrust washer, circlip, bearings and shafts, been collecting these for some years and finally found the last gear I was missing last year, not sure yet if I'll fit it in my restoration this year but may not if the old box still looks ok.

One of the pics shows mainshaft 2nd and 3rd gear, it's the one where the middle selector is fitted to it, what's concerning about that pic is the engagement slots on mainshaft 4th gear, that's the one right next to the fixed gear on the mainshaft, so closest to the clutch, the slot looks shiny, like something is wrong, there's also what looks to be a small sliver of metal sticking to the gear. I'd check that if I was you.

Has the box been apart before? might be that someone assembled it wrong, it's easy to orientate some of the thrust washer wrong and the circlips are meant to be fitted a certain way as well.

As Bryan says, there is a firm in Italy making really fantastic copies of the selectors, they are better made, have harder tips so should last longer and the finish on the surface of the selectors in just ace. Not cheap though, I bought all 3 in 2022 and the cost then was 150 euros for each selector, 300 for 2 but an offer of 400 euros for all 3 plus postage.

Pic of the middle selector compared to a NOS Honda one.



You need any details PM me.

Wow, those are nice parts!
I'm about to tear into a well-used 500 engine for the book. Maybe I'll try those if it's buggered up?

[Oddjob]

It's also the tactile feel of them Mark, like stroking wet velvet.

If you need a NOS selector for the rebuild let me know, you know where I am.

I'm also in possession of the biggest stock of 500/550 main shell bearings in the world I reckon, well over 100 black shells alone, even have some yellows and a few greens and browns although I'm not selling them yet. When the average price goes over £30 a shell I'll sell what I don't need. I'd make an exception for you though Mark if you needed any.

[HondaMan]

It's also the tactile feel of them Mark, like stroking wet velvet.

If you need a NOS selector for the rebuild let me know, you know where I am.

I'm also in possession of the biggest stock of 500/550 main shell bearings in the world I reckon, well over 100 black shells alone, even have some yellows and a few greens and browns although I'm not selling them yet. When the average price goes over £30 a shell I'll sell what I don't need. I'd make an exception for you though Mark if you needed any.

Wow, thanks, what an offer! If I get in that spot, I'll drop you a line.
I'm working (once again) on the 500/550 book, got a 500 engine finally so I can make the required pictures. I haven't decided yet on whether I will put the 500 and 550 'sections' of the Tranny work in the same chapter, or separate them: I tend to think there's enough difference between them that having separate chapters may be wiser in the long run to prevent confusion for the newbie using the book. They are so different as to be fully separate engines behind the crankshaft, IMHO. Forward & above of there, they aren't much different, side-by-side.

[bryanj]

Just to confuse it more a couple of gear clusters are the same 500 to 550