Old cg 125, gear ratio changes, what to do???

[tahx]

Hello people. i own a cg 125 2005 ( Pakistan edition), and im from Bangladesh , so we dont get the international ones here. it has only four gears.

i had recently changed the clutch plates and straight out of the garage, is seemed to run fine.

the problem started from next day, i noticed the gear ratio has changed.

for example changing from 2nd gear to 3rd gear, i used to get the end of gear RRRRRRRR sound on like 30/35 kph, now it starts revving on around 20 kph. so while on the first day , i could get like 50-55 kph on 4th gear, now im getting around 40.

is it the clutch plate or something else. please help me out guys! TIA

[uberkron]

The ratio cannot change without sprockets or gearbox internal gearset being changed.
Check that it is your bike, check chain tension and check clutch free play.
More than likely clutch is slipping.
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i ride a zip 50 2smoke. It overtakes a hundred times a day.

[tahx]

i changed the whole sprocket set like 2 months ago. so its unlikely to be worn that quickly. and havent touched the gearbox so cant tell anything about that.

tbh im a novice and i dont have very good mechanics here those can troubleshoot by themselves ( at least it seems so)

ill check up on the clutch slipping, lets see if its the reason

[Azoth]

You presumably changed the plates because you thought they were slipping. Now, you get less speed in top gear, so, assuming the clutch is to blame, you really do have slipping now, or else you haven't adjusted your clutch cable properly. Check clutch cable tension and free play first. There should be some free play before the biting point. Then check you installed your clutch plates and springs properly. You replaced the springs? Compare the length of the new ones with the old. The new ones should be slightly longer.
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Safety in numbers

[tahx]

well i havent changed the clutch plates since i bought the bikes ( almost a year and a half) and my shifting used to be really stiff. mechanic suggested to change the plates as they have worn off so i did.

checked the cable tension and free play, it seems fine. has a small bit free play before the biting point, shifting is smooth now.

but i didnt change the springs, only the bearing that was inside needed to be changed as it was in shit condition. should i reinstall everything?

[Teflon-Mike]

OK... 'Gear Ratio' number of turns of the back wheel caused by the number of turns of the crank shaft.

Crank shaft turns a cog, that turns a drum, in which the clutch sits.

Drum contains plates that are pressed against other plates to transmit 'drive' by friction onto the gearbox input shaft.

More cogs in the gearbox turn other cogs, that make the out-put shaft and 'drive' sprocket turn. that tugs the chain which makes the wheel-sprocket turn.

Overall gear ratio, is still number of crank shaft revolutions per rear wheel revolution...

The condition of the final drive chain & sprockets does NOT change the gear ratio.

The condition of the clutch, does NOT change the gear ratio.

The chain & sprockets can only change the ratio, by replacing them with ones that are a different size.

The clutch;

With the plates pressed together, effectively locking the drum to the shaft, will turn as driven by the crank shaft and transmit 'Drive'

With the plates 'released', the drum spinning with the crank-shaft, half the plates inside it spinning, but not dragging the other half round with them, does not transmit drive.

When 'engaged'; the 'input' turns one revolution, out-put HAS to turn one revolution; there is no 'ratio' it's 1:1.

When 'dissengaged'' the input turns as many revolutions as you like; the out-put doesn't turn. again there is NO 'ratio' its infinity divided by zero.

OK... onto your symptoms. You describe the bike not going 'as fast' as it did before you changed the clutch, and try and describe some sort of engine noise.

I assume your CG doesn't have an engine rev counter; so you DONT actually know how many rpm's the crank-shaft is turning for any given road speed... just what the engine sounds like....

And engine sound is deceptive; it changes both with the revs, but also with the 'load'. Note gets higher with higher revs, but it also gets deeper with more load put on the engine, like when you ride up a hill, so it can 'sound' like it's not turning so many revs, merely because its making more 'force'.

Such subtlety isn't going to help us; BUT I mention it so we can throw away some of the confusion!!

Problem... before new clutch.. bike went 50Km/h, now after replacing clutch you only can go 40Km/h....

Logical presumption would be that the clutch 'slipping' at higher load.

Works as it should, when not asked to transmit much force, but under load, the force clamping the plates together when 'engaged' isn't sufficient to keep them 'engaged', and when the force on the back wheel is as high as the clamping force, they unintentionally 'dissengage'.. when that happens, load is removed from the plates as they 'slip' and the bike, will start to coast and so slow down... which reduces the 'load' on the clutch again, and when it drops beneath the clamping force, they 'bite' again, and the clutch transmits 'some' power again, making the bike accelerate, which increases the load until it slips again, but, its going around that cycle very quickly, so it's almost happening at once, and what you get is a 'partial drive', the clutch slipping neither properly engaged or dissengaged, and the engine revs not linked in any way to the wheel or road speed.

And you say 40Km/h is as fast as you can go, so we have to assume that that is the speed where the 'load' about matches the clamping pressure you have on the clutch plates.

You say you have changed the clutch.....

So, again, we have to presume you have not done the job properly, OR there is a fault in the 'new' parts you have fitted.

Go back; look at what you have done.

Is the clutch cable properly adjusted so that the clutch can fully dissengage?

If it was adjusted up to compensate for wear on the old clutch, fitting the new one, without any wear, likely to mean the clutch cable isn't letting it fully disengage.

In removing the cable, to reove the primary drive cover to get at and replace the clutch;

- Have you changed the adjustment of the cable?
- Have you re-fitted the cable in-correctly?

Beyond that, you will need to open the clutch cover back up and have a look inside..... stupid question time...

- Was there any oil in the engine when you took the primary drive cover off? DID you put any back after you replaced it?

Without oil.. the engine wont run for very long before it siezes up... but also likely to 'cook' the friction material of teh new clutch plates; making them very hot very fast, and polishing them so they don't have the same friction properties to transmit drive.

Moving on;
https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/LD07%20Eng%20Build/100_0472.jpg
That is the generic 'Small-Honda' clutch.. as used on the CG125 (though photo is of it in a CB125).

See HOW2: Overhaul Clutch (Small Honda's +)

https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/LD07%20Eng%20Build/100_0503.jpg

The release plate removed by undoing the four M6 bolts, you can easily get at, reveals the clutch-hub nut.. an annoying little thing with four notches rather than 'flats' that requires a 'special' castle nut socket to undo it, rather than an ordinary one....

Special socket is ALSO designed to fit through the release splate WITHOUT removing it from the hub.. just slipping the release rod and bearing out of the middle......

Which isn't so critical when taking it all apart... but IS when you come to put it back together, because without the special socket, you have to put the clutch 'pack' back in without any spring load on the plates to hold them together, and they have a habbit of getting misaligned... and if they do that... the clutch WILL NOT full dissengage.. if it will even engage at all!!!

Can be taken apart and put back together without the special tool, or making a special tool as I did in that HOW2......

BUT.. usually results in that poor hub nut being mangled to buggery being bashed around with a screw-driver or chisel or something, when its un-done... and even more mangled when it's put back on, where its incredibly likely it just wont be properly tightened.... will go on and can be locked in place with the lock washer so the clutch doesn't fall apart... but.... not fully screwed down, the 'play' from it not being fully tightened will rob clutch 'travel'.. and again.. you can bugger it up so that the clutch wont fully 'engage' or fully 'disengage' either or both!

Also potential in there to get the release plate on 'cock' doing up one bolt all the way at a time, so it looks like its all as it was, but pulled down more one side than the other, again, it doesn't have the full range of travel, and teh clutch might not fully engage or disengage or both.

More potential for error in re-assembling the primary drive cover:

https://i178.photobucket.com/albums/w269/teflons-torque/Little%20Dreams/LD07%20Eng%20Build/100_0496.jpg

As shown in this pic; the clutch release 'rod' is pushed by a lever in the cover, worked by the clutch cable.

Possible to put the cover back on, without the rod properly seated in that lever, so again, it may not fully engage or dissengage; but also, if the cover isn't fitted up properly with a good gasket, it can sit 'skew' and again effect clutch travel, or if no gasket is fitted, sit too close to the clutch, and constantly apply disengagement travel, or conversely, if too thick or too many gaskets between cover and engine cases, it can effect the travel and prevent full travel, or do 'strange' things to the action, as the lever 'over centres' working in an arc it wasn't intended to.

After eliminating any errors YOU might have caused fitting the new clutch incorrectly... we might get to the question of whether the 'new' clutch you fitted is faulty. And did you fit new springs with it? and did you 'soak' the new plates in oil over night before fitting them?

Potential causes of your problem are MANY...

and I am however many million miles away, without the bike infront of me... I cant do much more to help you fix it.

See the How 2.. its all laid bare and shown in photo's how it fits together and should be fitted; compare to what you have done; re-visit what you have done; make sure you have done it properly.

And good chance tour problem will be solved.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'

[tahx]

i figured that shouldnt have written gear ratio. please excuse me as im a newbie to this.

this was really informative. i will go through everything again. lets hope it solves the issue.

btw i didnt soak the plates overnight, guess that was a mistake. there wasnt any oil when i took the cover of, i already took out the old and i put new oil after i replaced it.

thanks a lot guys ill update soon

[Hong Kong Phooey]

You didn't by any chance just us any old nearest to hand car oil when filing it up again did you? Has the clutch cable adjustment been checked / mentioned?
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'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8