CG125 noises in neutral

[scotto75]

Hello

I’ve had the rear wheel off to sort out the brakes out, and when I was adjusting the brakes with the wheel back on, I noticed that there was a clunky sound coming from the engine when the I spun the wheel in neutral.

It usually spins freely, but now when rolling in neutral there’s something causing friction and I can hear and feel a slight juddering.

The engine runs and gears change as normal, but underneath is this clunking.

Chain tension is fine and there is enough oil in the engine. Can’t work out what it is, but have decided not to run it until I know what’s up. I have another engine I may bung in it for the time being, but would like to run some diagnostics before I do..... any ideas would be really appreciated.

Thanks!
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Honda ‘73 CB350, ‘80 CG125, ‘88 CG125, '73 Triumph T140V

[Nobby the Bastard]

Sprockets are worn.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[xX-Alex-Xx]

[oilrag]

Stating the obvious but if there was no noise before you did the work and now there is a noise chances are the noise is because of something you did. The chain not being straight would seem the most likely cause of a clunking noise. Does the noise only happen when the chain turns? It could also be that you put wheel spacers in wrong so the rear wheel is misaligned. The extra resistance could be caused by those things or maybe you have adjusted the brake too tight. You should probably go over everything you did again.

[scotto75]

Thanks for the replies.

I removed the rear wheel and the sprocket and checked the cush drive rubbers, which were all good.

I removed the front sprocket, which was a new non-genuine part bought four or five years ago from Wemoto (same as the rear) and noticed the fixing plate teeth were worn which caused some slight play. There was also a bit of movement in the countershaft. I replaced the front sprocket and plate with a genuine but used set off my spare engine. I’m now aware that the one I took off is thinner than an original Honda item.

I reassembled everything using a clean and lubed chain. I adjusted the chain tension and wheel alignment.

With the bike jacked up, I spun the rear wheel and could hear the crunching sound coming from the countershaft. It’s the sound of knackered ball bearings rubbing together when done up too tight.

If I had to guess, I’d say the countershaft bearing has gone. I’ll stick the (untested) spare CG engine in over the weekend and hope that it’s a goodun and not a dud.
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Honda ‘73 CB350, ‘80 CG125, ‘88 CG125, '73 Triumph T140V

[jeffyjeff]

Due to the offset between the swingarm pivot and the countershaft, the chain slack tightens as the suspension is compressed. For this reason I check my chain tension while sitting on the bike (rear suspension full sag). This results in a chain slack that is a bit looser than spec, if checked when the suspension is unloaded. But by running the chain a bit on the loose side (still fully within spec when motoring down the road), I know the chain is not placing undue stress on the countershaft bearing. Just one man's opinion.
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History shows again and again how nature points out the folly of men - BOC

[bikenut]

That's how it's supposed to be done.

If your not sure what above means, draw a sketch of the set up, you may need a compass, the drawing set type, and possibly a ruler.

See the difference ?

You can set up tension "loaded", then unload and make an "indicator " from some tin and mark for tension when loaded, then it's easier than sitting on bike etc.., or get an assistant to sit on the bike to load suspension etc., Etc. Etc....
An over tight chain will ruin stuff like the chain, sprockets, cush drives, wheel bearings, swing arm bushes and yes, gearbox output shaft bearings.

See CMSNL exploded views for what's involved in replacing the "now possibly uncaged balls" in the bearing, etc. etc. etc.

It's gunna be a full strip down etc..

Enjoy...
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nuts about bikes

[jaffa90]

PostPosted: 01:38 - 10 Feb 2021 No Rating Post subject: Reply with quote
Due to the offset between the swingarm pivot and the countershaft, the chain slack tightens as the suspension is compressed. For this reason I check my chain tension while sitting on the bike (rear suspension full sag). This results in a chain slack that is a bit looser than spec, if checked when the suspension is unloaded. But by running the chain a bit on the loose side (still fully within spec when motoring down the road), I know the chain is not placing undue stress on the countershaft bearing. Just one man's opinion.
____________________
History shows again and again how nature points out the folly of men - BOC
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bikenut
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PostPosted: 16:12 - 10 Feb 2021 No Rating Post subject: T Reply with quote
That's how it's supposed to be done.

If your not sure what above means, draw a sketch of the set up, you may need a compass, the drawing set type, and possibly a ruler.

See the difference ?

You can set up tension "loaded", then unload and make an "indicator " from some tin and mark for tension when loaded, then it's easier than sitting on bike etc.., or get an assistant to sit on the bike to load suspension etc., Etc. Etc....
An over tight chain will ruin stuff like the chain, sprockets, cush drives, wheel bearings, swing arm bushes and yes, gearbox output shaft bearings.

See CMSNL exploded views for what's involved in replacing the "now possibly uncaged balls" in the bearing, etc. etc. etc.

It's gunna be a full strip down etc..

Enjoy...
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Been stating this for years, you need chain slack when fully loaded.
Some muppets on here state refer to handbook settings when on the side / centre stand.

[redeem ouzzer]

Why do we have to have this autism about tightening a chain every few months? Set tension as per the manual, job done.
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Be a REAL MAN!

[bikenut]

A good manual will tell you to set the chain tension as so, knowing that when the suspension is at mid stroke ( do a scale drawing as offsets will effect what's coming next, unless the front sprocket is on the swing arm pivot point as on some completion/scramblers etc ) ish, the chain tension will be sufficient, but how many people would consider that "slack" to be tooo slack, and adjust untill "correct" at that relaxed suspension position, meaning the chain in reality is tooo tight.

Do you when adjusted check the chain tension when the suspension is loaded ?

Of course this completely ignores any "tight spots" etc..
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nuts about bikes

[redeem ouzzer]

I don’t need to check it when the bike is loaded. The considerable R&D resources have calculated that if the slack is in tolerance with the bike on the stand then there will be sufficient slack to cope with the available suspension movement. Every bike I’ve had has the chain tension mentioned purely under the bikes normal weight, not with my fat arse parked on it. If I tried to run the chain on my 1100 at 30mm slack under load it would slap all over the place and be dragging on the floor when the bike was unloaded.
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Be a REAL MAN!

[Robby]

I agree.
The chain gets about an inch of free play, same as on every chain I've set for the last 20 years.

I think the autism about setting the chain tension with someone sat on the bike comes from competition motocross bikes with insane amounts of suspension travel, and got copied across into people thinking they have to do it on their 125 with a couple of inches on travel.