Strange gear behaviour

[hardleydavidson]

Hi,

Bit of a novice, I've got a weird problem with my little 50cc, it's a 4 down gearbox (139FMB - C50 Clone), I can go from neutral to 1st no problem however to move in to second I have to raise the selector a bit with my toe and then back down in to 2nd, same for 3rd and 4th, back up to N is no problem. Could this be the selector rod? does it need adjustment?

Each gear change requires a little lift before it will change?

[Stu]

the pivot point of the selector may need to be lubed up depending on the setup

Drop a pic of the selector

[Ian Frog]

Is it possible there is a spring somewhere that normally does this return of the lever movement when you change?

If so I would hope for an easy replacement situated on the shaft under the gearbox cover.

Cheers

Ian

[Stu]

Is it possible there is a spring somewhere that normally does this return of the lever movement when you change?

If so I would hope for an easy replacement situated on the shaft under the gearbox cover.

Cheers

Ian

 

There probably is but a more common problem is a seized gear lever pivot but that depends on the lay out of it

[Ian Frog]

Interesting [mention]Stu[/mention] I hope he posts the picture now so we can see.

Cheers

Ian

[Stu]

If its this type then the bit can seize

 

[hardleydavidson]

Thanks guys, here it is, needs a clean that's for sure

http://www.systemben.com/images/kin2.jpg

http://www.systemben.com/images/kin1.jpg

[hardleydavidson]

My first thought was it feels like a spring is missing but I can't see anywhere a spring could attach. When I took the pics just now the rod feels quite slack, should it be? if not I can't see any way to shorten it as it's already at it's maximum shortness (if that makes sense)

[Ian Frog]

First things first get yourself a better picture from straight in front and level.

This will help you on reassembly.

You are going to be removing the whole assembly in 1 and trying not to let it twist and alter the connecting rod length you should lay it on a cloth or card surface and thoroughly clean then lubricate the whole thing paying particular attention to the pivot point as highlighted by [mention]Stu[/mention] earelier then put it back on and try it out.

Then if that works we can discuss rust removal from the linkage rod.

Cheers

Ian

[hardleydavidson]

Awesome thanks

It's an ongoing project bike. Was fun when it was on the road but has been sat for a couple of years as I had a clutch issue I couldn't resolve, but, thanks to lockdown boredom I finally fixed it Saturday. It's Chinese but I'm slowly swapping out parts as and when they fail (which happens a lot) for Honda equivalents. I'll try and remove the rod assembly this evening after work and give it a good clean.

[Guest Swagman]

And if that doesn’t work then it may well be as Stu said, inside the cover there may well be a centralising spring that has come of or snapped.

[fastbob]

And it will look pretty much like this . But as mentioned , it might just be grit and filth in the external mechanism making it sticky . Cheap solutions first , don't jump to conclusions . ( I already have by the way , it's a worn out or broken spring ) Don't be freaked out by this picture , it's easier to get at than you might be thinking .

[hardleydavidson]

Thanks guys, this is really helpful, it'd be great to see it back on the road, it's only a little bike, more of a toy really, but a fun project all the same

[fastbob]

Thanks guys, this is really helpful, it'd be great to see it back on the road, it's only a little bike, more of a toy really, but a fun project all the same

 

I'm at work right now but I'll have a look into this later on ( there's F A else to do ) and stick up a few pictures of what you might have to do to fix this .

[hardleydavidson]

Ok, so I've removed the assembly, not a spring in sight, both ball joints seem to move ok and aren't seized in any way, could it be that there was a spring once that's now deteriorated at some point?

http://www.systemben.com/images/kin3.jpg

http://www.systemben.com/images/kin4.jpg

http://www.systemben.com/images/kin5.jpg

[fastbob]

Ok, so I've removed the assembly, not a spring in sight, both ball joints seem to move ok and aren't seized in any way, could it be that there was a spring once that's now deteriorated at some point?

http://www.systemben.com/images/kin3.jpg

http://www.systemben.com/images/kin4.jpg

http://www.systemben.com/images/kin5.jpg

 

No no no the spring is inside the engine . Luckily it's usually not buried deep inside and is usually to be found under the crankcase side covers . I've built an engine or two but never done a C90 / 50 based one . Give me a while and I'll show you where the spring lives .

[Stu]

give them all a good clean and lube and stick it back together and see how it is

If no different then time to check the detent spring

[fastbob]

Ok here's the best I can do . This is a video of a Stomp Pit Bike but because these engines and countless others are all based on the original Honda C90 Cub , the gear change mechanism is basically the same . Yours may not have the same problem but this will give you an idea of what you are up against and how to tackle it . The spring that I suspect lies at the heart of your problem is highlighted in the still photo . Good luck . https://youtu.be/tdmd7z5qwag.

[hardleydavidson]

Thanks guys that's brilliant!!

So, the plan is to clean and grease up the assembly and try it, if it still doesn't work then remove the crankcase and have a look at the spring. I'm guessing as I'm opening it up I'll need a new gasket. Never opened this side before, the clutch side was easy and seeing as I drained the oil when I fixed the clutch it's a good time to tackle this. It'll have to be a weekend job, but seeing as Friday is a bank holiday I'll attack it then.

Is it worth reattaching the assembly while case is off to test? or am I likely to ping all kinds of cogs and springs around the garage?

[Ian Frog]

And if that doesn’t work then it may well be as Stu said, inside the cover there may well be a centralising spring that has come of or snapped.

 

Ahem ! as mentioned by someone other than [mention]Stu[/mention] lol.

The spring shown on the parts diagram is inside the casing that the gear lever mechanism bolts to the outside of.

Cheers

Ian

[Ian Frog]

Hi [mention]hardleydavidson[/mention] Could you post a picture of that side of the bike please.

I think there is a good chance you wont be needing a gasket but I would like to have a look first.

Cheers

Ian

[Ian Frog]

Lol Cancelmy input I think [mention]fastbob[/mention] has nailed it for you.

Cheers

Ian

[hardleydavidson]

Hi,

Just found this...

It's the gear selector arm from the same engine as mine, I'm guessing the spring is buried pretty deep inside? on the clutch side of the main engine block maybe?

[Ian Frog]

Yes.

If you watch [mention]fastbob[/mention] `s video you will see it`s actually quite easy to get to just removal of the clutch basket. Please layout any plates you remove in the correct order so they go back in right, they sometimes have small differences.

Cheers

Ian

[hardleydavidson]

Ah yes!! Just spotted on an online video, you can see the selector and the spring under the clutch, that's a doddle, had the clutch off more times than I can count, annoying thing is I've only just reassembled it all