Motorcycle Owners Club

Honda CG125 but also some universal motorcycle information

Honda CG125 Chain

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Chain Oiling

You will know when to oil the chain by looking at it, and or kick the back wheel round (if it feels notchy it needs oiling).
If you do not have a fully enclosed chain, I would check the chain every time it rains when it has dried.
I found (without a fully enclosed chain) it's not mileage that effects when you need to oil the chain, it's time and rain.

To oil the chain, make sure it has no water on it, it's probably best to oil the chain when it's hot just after a ride.

Spray the chain with oil on the inside (the side that makes contact with the sprockets),
the oil will fling outwards when bike is used and oil the outside.
Do not spray the outside of the chain since it will just fling off and create a mess every ware.
Motorcycle Dry (WAX) chain lube probably will not fling,
so you may have to spray every part of the chain (see instructions on can).

The best advice is to oil a chain often but not with a lot of oil.

Chain oil is slippery so wipe off any that gets on to the tyre.

Do not ride the bike for at least 1 hour afterwards; else the oil will immediately fling off.

What Chain Oil to use

By far the best way to lubricate a chain is with chain grease, see my Motorcycle Chain Grease page,
but it does not work on O, X or Z ring chains (small rubber seals slightly visible on each end of every roller on the chain).
O, X and Z ring chains are very expensive, I and others do not like O ring chains,
see Replacement Chain section for more details.
It's also common not to use chain grease every time the outside of the chain needs lubricating,
so the methods below are still needed.

All of the following will work on any type of chain.

What type of chain lubrication to use is very controversial,
everyone has their own preferences (including mechanics),
no one knows which is best for chain resistance or life (except for Motorcycle Chain Grease, see above).

Motorcycle Dry (also called WAX) chain lube is in spray can form, the one everyone seems to like is made by Wurth.
Nearly all customers who buy the Wurth chain lube and write a review, believe it's the best chain lube they have ever used.
The main thing they like is the fact it does not fling all over the back wheel and the bike (and it's dry to the touch).
But what nearly all of them fail to mention is the downsides of using a Dry chain lube, which there are several.
I'm not sure, but if the chain had anything other than dry (wax) chain lube on it before,
you may have to remove it with chain cleaner.

The other type of motorcycle chain lube in a spray can is the oil type.
People who do not like the dry (wax) chain lube like the oil type because it's wet and flings.
Their logic is you can see which parts need oiling and when.
The fact it flings off the chain means when you put it on the inside of the chain, it will be flung out,
covering the rest of the chain when the bike is used (may be even in to the chain more as it heats up and stretches).
The more it flings off, the more dirt and rubbish it will take with it (so do not need to clean the chain as much, if at all).
At the moment this is the type of chain lube I'm using and it's Silkolene Chain Lube (normal version, not gel version).
But I have not compared it with others, so I cannot say what it's equal to or better than.

What bad weather riders often hate about spray can chain lube is,
it's common for it to completely wash off in medium to heavy rain.
But I found water also lubricates a chain, until it dries.
Some people have found thick sticky chain lube sprays that stay on in the rain, but all the dirt and grit also sticks to it,
making a terrible grinding paste that wears out the chain and sprockets very quickly, this should be avoided at all costs.

Engine oil is not recommended (it's too thin, will just fling off very quickly).
But can be used since it's cheap.

Gear Oil (gearbox oil) SAE 80W or 90W can be used,
there are pros and cons for using this like all the others.
If you're riding in a lot of rain or wet salty roads in winter, this may be the best?

And finally there are the devices that oil the chain, while the bike is working.
These are popular with long distance, high mileage, all year round, all weather motorcyclists.
As well as people who have no way of lifting the rear wheel off the ground (no centre or paddock stand),
since they cannot rotate the back wheel.
Cheap manual options are
Tutoro (I have had a report it's not secured near the chain / sprocket and so was caught and flew off while in use).
Loobman, as long as you do not have a fancy high end motorcycle, you should find a place to fit it,
it will have to be removed when you wish to take the rear wheel out (so it's a bit of a pain).
And if you squeeze the bottle to hard it may leak.

So after reading all this, you may be asking what should I put on the chain, my answer would be.
Try the Silkolene Chain lube first.
Then if you wish try the Wurth Dry Chain lube.
And finally try the Gear oil.
Make sure you try all 3 in all weather conditions and work out which is best for you or the chain.

Chain Tension

See Owner's Manual and the information below, if you don't have the Owner's Manual you can manage without it.

If bike has been used, let it cool down overnight.
Chain Tension should be 20 mm in the middle of the chain at the tightest spot.
To measure, put a ruler or stick (with marks on it) next to the middle of the chain (just in front of the rear passenger foot rest?).
(If you have a fully enclosed chain,
you should find a small round cover that can be removed to inspect the chain around that point).
Put your finger under the chain and try to push it up until you feel slight resistance.
Move the back wheel slightly and recheck the chain, keep doing this until you find the tightest spot.

All chains have or will develop tight spots along the length of the chain.
Often tight spots will develop due to a lack of oil or grease.
Putting excessive amounts of oil (see Chain Oiling above for what oil should be used) all around the tight spot
(on top, underneath and on the sides),
then pushing the chain up and down and then putting more oil on again,
may remove the tight spot or reduce it.
But when the chain is used for a few miles, loads of the oil will fling off and the tight spot may return.
Oil will never be anywhere near as effective or as long lasting at fixing tight spots, as grease,
see my Motorcycle Chain Grease page.

If the chain is excessively tight (much lower than 20 mm, maybe lower than 10 mm) at the tightest spot,
it can damage the gearbox (very bad idea and expensive, do not let it happen).
If it is excessively slack it can also cause trouble.

A chain that has just been oiled will be slacker than normal,
after a few miles the chain will tighten up to normal as the excess oil is thrown off.
So if I have to check the chain tension after I have just oiled it,
I personally wait for around 50 miles for the excess oil to be thrown off.

How to adjust the chain tension

Slacken the right hand rear wheel axle nut (22mm ?).
The nut is normal type, anti-clock wise to slacken, clockwise to tighten,
if you're not strong enough to slacken it, tap / hit the spanner with a hammer several times quickly,
if that fails get a longer spanner (to get more leverage).

There may (may not) be a small pin stopping the nut from being slackened, called a Cotter pin,
it's basically a piece of metal folded in half, it goes through a hole near the end of the screw thread.
The 2 pieces that have gone through the hole
are then separated and folded up and around in opposite directions around the nut.

There are 2 adjusters, one on each side of the axle,
they both have 2 nuts (12 ? and 10mm ?, the one on the end is a locking nut).
Put a spanner on both nuts at the same time, and slacken the end one.
Repeat this on the other adjuster.
Tighten the nut (not the end one) by the same amount of turns on each adjuster (or wheel alignment will go out),
recheck chain tension.
The adjusters should point to little marks (1 in diagram) on the frame,
they should be the same on both sides or the wheel alignment will be wrong.
If your wheel alignment has been checked professionally (part of the MOT in the UK),
you do not need to worry about the marks.
One of the adjusters should point to a label on the frame that has a wear indicator, when it says it's worn out replace the chain.
When you replace the chain also look at the gearbox and back wheel sprockets (they move the chain around) for wear,
search internet for a universal guide.

When tightening the rear axle nut,
push the rear wheel in to the bike with your left hand while tightening with your right hand,
do not try to tighten the adjuster nuts, just lock the locking nuts in place (put a spanner on both nuts at the same time),
to check that the adjuster nuts are tight, try to put a piece of paper between them and the frame
(if they are not tight slacken rear axle nut and this time push harder when tightening the rear axle nut).
Recheck chain tension and repeat procedure if necessary.

Adjusting the chain (tightening the chain) will reduce the free play in the rear brake pedal
(especially if you had to tighten the chain a lot),
so check the free play and that the brake light comes on when it's used, see Rear Brake in the Brakes page.

Replacement Chain

Chains and sprockets wear due to each other.
So putting a new chain on worn sprockets will excessively wear the chain and vice versa,
as a result it's normal to put new chains and sprockets on at the same time (called a chain and sprocket kit).

Buying the right make of chain is important,
low quality makes often do not last long and some even snap (very dangerous and may damage gearbox),
I would avoid any chain that's not made in Japan.
DID is the most common make sold in the UK (and is based in Japan).

125cc chains often have the option of clip link or rivet link,
this is a single link that when removed splits the chain in half,
so you can take the chain on or off the bike.
A rivet link is very hard / almost impossible for a normal person to take on or off (O and X ring chains often have them).
A clip link is very easy for anyone to remove.

When you buy a chain, it's often cut to the correct length (amount of links) for your bike by the shop or manufacturer;
it's very hard without the right tools to cut it yourself.
The best way to be absolutely sure is to compare it to your old chain (unless it was wrong in the first place).

The easiest way to replace the chain is to split the old chain, attach one end of the new chain to the old chain,
then rotate the back wheel to pull the new chain over the sprockets.
The new chain will be much tighter than the old (since it has stretched), so you will need to adjust the chain adjusters a lot.

Front Drum brake model, since you have a fully enclosed chain guard, water and other things cannot get on or in to the chain.
So you do not need an O or X ring chain (these are expensive),
more information about these chains are in the Front Disc brake model section below.

Front Disc brake model original chain is O ring type,
which costs several times more money than a non-sealed chain (no O, X or Z rings),
but it's meant to last several times longer by keeping the internal grease inside due to the O or X rings
(and stops water and other things getting inside it).

I have found this article about chains
Most 125cc bikes use a 428 size chain, so their recommendations of makes and models do not match,
but their advice about chain types is useful.
As a result of their advice and my experience, I will try to avoid O ring.
O rings also have a reputation for slowing down a motorcycle compared to any other chain (due to their design = resistance).

Honda CG125 Front Disc brake model,
see last paragraph in the sprockets section below to make sure you get the right sprockets for it.


The sprockets are what the chain attaches to;
you have a large sprocket on the back wheel and a small sprocket on the gearbox shaft.
Chains and sprockets wear due to each other.
So putting a new chain on worn sprockets will excessively wear the chain and vice versa,
as a result it's normal to put new chains and sprockets on at the same time (called a chain and sprocket kit).

Search the internet to see what a worn out sprocket looks like,
they start to turn in to hooks, pointy or even snap off in extreme cases.

The small sprocket on the gearbox shaft often wears out far quicker (picture above is quite worn)
than the rear sprocket and the chain.
Some people say the front sprocket may wear out twice as fast as the rear, so you have to replace it twice as often.

The other thing that can happen is the front sprocket can wear out between it and the gearbox shaft,
this is only easy to see when you have the back wheel out of the bike (see How to remove and install the wheels in the Bike),
or split the chain so most of the chain tension is off the sprocket.
If you find the sprocket excessively wobbles on the gearbox shaft, it is worn out.

Getting a good look at the front sprocket may be easy or a little bit harder.
On some models all you have to do is remove the Gear change lever and remove a little cover.

If you have a fully enclosed chain guard, to remove it see Enclosed Chain Guard

To replace a sprocket, you need to remove the chain tension by removing the back wheel or splitting the chain.

The quality of sprockets varies dramatically from make to make.
In the UK, it looks like most shops and internet companies that sell sprockets, sell them with chains together.
They normally give you the option of what type and make of chain you want,
but do not tell you what make of sprockets you will get.
The most common sprockets supplied are made by JT Sprockets; they have a reputation for being OK.
There are however Chinese manufactures making sprockets that are so bad,
if they do work, they may wear out after a very few miles.
And of course they excessively wear the chain, so it's a massive financial mistake.

When replacing a sprocket, always check the new one has the same amount of teeth as the old one, before fitting it.
If they are not the same, check the old one was correct in the first place.
Since the wrong amount of teeth will affect the gearing of the bike.
It's not unknown to buy a chain and sprocket kit for a bike or just a sprocket,
and find it has a different amount of teeth than it should have.
This is often due to whoever packed the sprocket put the wrong one in (at the manufacturer or distributor).
The other reason could be they have discontinued making the sprocket with that amount of teeth
(they should warn you of this before buying).

Honda CG125 Front Disc brake model (UK and Europe)
It should have a 14 tooth sprocket on the front and a 45 tooth sprocket on the rear (that's what Honda put on originally)
Lots of sprockets are being delivered with 44 tooth on the rear (JT Sprockets claim to only make a 44 tooth).
If you are lucky you will see it advertised as 44 tooth so you can avoid it.
I tried a 44 tooth and it was disastrous,
the bikes acceleration suffered and it had real trouble with head winds (due to a 1.5 mph increase in peak power in 5th).
If you have no choice but to use a 44 tooth on the rear, put a 13 tooth on the front,
this will reduce peak power by 3.4 mph in 5th gear (compared to 14, 45).
See MPH to RPM page for the MPH to RPM of the 14, 45 sprockets.
The only quality 45 tooth sprockets I have found in the UK are a genuine Honda one
that is only available in a chain and sprocket kit (which is all I have ever used, since the kits last around 18000 miles),
and Afam claims to use high quality metal in their sprockets (available individually or as part of a chain and sprocket kit),
in the UK only a few shops sell Afam but you can also buy direct from the importer at

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