Chain

Honda CG125 Chain

Chain Oiling
Even O ring and fully enclosed chains need oiling.
Use a motorcycle chain oil, there are arguments for and against motorcycle chain wax so oil is recommended.
Engine or gear oil is not recommended (will just fling off very quickly).

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 its dried.
I found (without a fully enclosed chain) its not mileage that effects when you need to oil the chain, its 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.

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.

The better the chain oil, the more it will stick on (not fling off), it will also last longer and resist water.

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.
Sometimes tight spots will develop due to a lack of oil.
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.

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.

A chain that has been severely neglected with a lack of oiling will become tight along the entire length of the chain or have a very large amount of tight spots.
Even rust can develop (oiling may remove light rust over time).

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 your 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,
its 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 though 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).
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 allot),
so check the free play and that the brake light comes on when it's used, see Rear Brake in the Brakes page.

The original chain on the front disc brake model is O ring type, this costs several times more money than a non O ring chain,
but it lasts several times longer and keeps the internal oil inside it due to the O rings (and stops water and other things getting inside it).
I advise you stick to the manufacturers choice. Of course a X ring is even better than a O ring but costs even more.

The original chain on the front drum brake model is probably not O ring type, it may use a much cheaper type of chain because the chain is fully enclosed.
The main advantage of a O ring chain is when you do not have a fully enclosed chain guard around it,
the O rings protect the chain from getting water and other things inside it.
I can not see any point in fitting a O ring chain on a bike with a fully enclosed chain guard all around it.

Sprockets

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 heavily worn sprockets will excessively wear the chain and visa versa (so often people put new chain and sprockets on at the same time).
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 one and the chain.
Some people say the front sprocket may wear out twice as fast as 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),
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

Servicing

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