Oil

Honda CG125 Oil

How to change the Oil

How to check the Oil level

Which Oil quality to use

Centrifugal Oil filter

When to change the Oil
The Owner's Manual states change every 2500 miles front disc brake model or 1850 miles front drum brake model,
I would change it at 1750 miles front disc model or 1500 miles front drum model, if used for a mixture of short and long journeys,
if you are mainly doing short journeys, change it every 1000 to 1500 miles front disc model or 1000 miles front drum model.
The best advice is to treat the mileage in the Owner's Manual as an absolute maximum.
Short journeys are bad for oil, the engine does not get up to heat and condensation occurs,
this means the oil will become dirtier per mile than on normal journeys, so you need to change the oil at less mileage.

The quality of the oil, your riding style and the state of the engine will all affect how long the oil will protect the engine.
When the oil degrades the oil may be burned and you will notice the oil level drop on the dip stick (see How to check the Oil level below).
Running below the min mark can result in seizing the engine, the repair bill is often so high the engine is scrapped,
the electric start models seem to be far more susceptible to engine failure due to low oil.

The other reason for burning oil is the engine is faulty or a part is worn out.

My Honda CG125 (front disc brake model) oil level is still at maximum at 1750 miles but at 1950 miles its dropped to half way on the dip stick.
So I should at least top up the oil to the max mark or really should change the oil at 1750 miles or before.
Please note the mileage your oil will last will be different to mine, since your riding style, quality of oil and state of the engine will be different.
I know one person who put low quality oil in his perfect engine and he starts burning oil at around 750 miles.

Just because no oil has been burned does not mean its not in need of being changed, the oil can lose its protection abilities and not be burned.
For instance you might be able to go way over the recommended oil change mileage and not burn any oil, but the oil and filters become very dirty.
As oil becomes dirtier it will turn darker and darker until it eventually turns to black (which is bad, see Centrifugal Oil filter section below),
even the oil on the dipstick will darken, see How to check the Oil level section below.

Its probably a good idea to change the oil every year (maybe every 6 months), even if you have not done enough miles.

I highly recommend you read my Which Oil quality to use section below to find what Oil quality you should use.

How to change the Oil
Tools Required.
24 mm Spanner or Socket to undo oil drain nut (left hand side of bike near the bottom).
Front Drum Brake model may (depends on version) have another oil drain nut under the bike, needs a 17 mm spanner or socket.
Container to collect old oil (2 litre ice cream container or anything).
Rubber gloves to protect hands from oil.
Small funnel to help pour new oil in to bike (washing up liquid bottle, water bottle, pop or squash bottle cut in half and 100% cleaned and dry).

Warm up engine for at least 3 minutes (idling and revving).
You will get more oil out if you take the bike for a long fast ride to get the oil as hot as possible, the more oil you get out the better.
I have found 5 miles at 40 mph in 5th gear (nut not to hot) does not get as much oil out as 17 miles with over half of that over 50 mph in 5th gear (nut very hot).
Even with gloves on the nut is to hot to touch on the 17 mile trip, you end up dropping the nut unless you hold it with many layers of cloth or towel to insulate it.

Switch off engine and immediately

Put container under the bike to catch the oil
Put rubber gloves on hands
Remove the dip stick (big plastic knob, right hand side of bike, it measures the oil in the engine).

The Front Drum Brake model may (depends on version, often its only on very old bikes) have a drain nut underneath the bike (17 mm),
this should be used to drain the oil (not the oil filter / drain nut in the paragraph below).

Remove the drain nut (see picture below, if the gear change lever is in the way see Gear change lever in General page).
If the nut is to tight you will have to tap / hit the spanner or socket handle with a hammer or something quickly several times.
You remove the nut like any normal nut, anti clockwise to remove and clockwise to tighten.
If you use a spanner and it keeps slipping off the nut, try pushing it on to the nut while turning it, if that fails try a better quality spanner.
A socket will grip the nut far better than any spanner.

The drain nut (24 mm, left hand side of bike near the bottom) has a large spring & oil filter sitting behind it.
Use the spring to wiggle the filter out.

   The filter is made of metal with hundreds of very small holes in it.
   At one end it's round with about a 2.54 cm diameter, its about 2.54 cm long.
   The spring is round and about 2.54 cm diameter,
   it's about 5.1cm long but only has around two 360 degree turns in it,
   the spring is not compressed much.

Clean filter with a suitable liquid like petrol (don't leave in petrol to long or it will eat the rubber).
If you clean the filter with petrol, the petrol will evaporate very quickly in the open air.

The front disc brake model claims you only need to clean the oil filter every 7500 miles,
I would clean it more often, to stop the centrifugal oil filter having to clean the oil.
If you find anything major in the filter, look and think, if your worried show it to a mechanic,
its normal to get a bit of metal in there when an engine is running in.

The Owner's Manual for the front disc brake model claims the centrifugal filter should be cleaned every 7500 miles.
The centrifugal oil filter is inside the engine and never needs to be cleaned if you keep the other oil filter clean and change the oil on time or before,
according to the mechanics. For more details see Centrifugal Oil filter below.

The oil will continue to drip out of the bike for ages, rocking the bike on the centre stand might help get more oil out, also leaning the bike to the left slightly.
When its stopped dripping, or you can not wait any longer, put the filter, spring and drain nut back on.
Make sure the nut still has a black rubber O ring on it or its in the screw hole, if not find it, you may have dropped it in the oil container when you removed the nut.

Pour 900ml (1 litre bottles often have marks down the side) of 10W/40 new engine oil (see Which Oil quality to use below) in,
Check the oil level is at the max mark or above (see How to check the Oil level below), if it's below the max mark put more oil in until its at the max mark.
Warm engine up (screw dip stick back in first) for 3 minutes (idling and revving slightly in neutral) and check oil level after its been off for 5 minutes.
If the oil level has dropped below the max mark put more oil in until it reaches the max mark.

How to check the Oil level

Remove dip stick
(big plastic knob, right hand side of bike, it measures the oil in the engine),
wipe the oil off,
put dip stick back in bike but do not screw it in,
the xxxx marks at the bottom of the dip stick should face sideways (not up and down),
take dip stick out of bike and look were the oil has gone up to on the dip stick,
the xxxx marks on the bottom of the dip stick mark the min and max mark.
In the picture 2 is the maximum mark, 3 is the minimum mark.

Its much easier to see the oil in natural daylight than with a light bulb.
There's no harm going slightly above the max mark, but not excessively, never run the engine below the min mark (may damage or destroy engine).
Make sure you check the oil level with the bike on level ground.
There is an argument whether you should check the oil level with a cold or warm engine, with a warm engine make sure the engine is switched off for 5 minutes first.

See When to change the Oil section above to find out why it is so important to check the Oil level regularly.

Which Oil quality to use

Since the free 600 miles service I used real semi synthetic oil (Silkolene Comp 4 10W-40).
I was running in the engine, so I do not know what it did to the performance, but the clutch felt a lot smoother.

Real semi synthetic has Ester in it which will protect the engine when cold and also at high revs,
it will also not break down as fast at high engine revs,
so the oil will do more miles before needing to be replaced (I would still change it early anyway),
unlike mineral oil / fake semi synthetic oil.

Many oils claim to be semi synthetic but are in fact normal mineral oil.
If it has Ester on the label you know it is real semi synthetic or real fully synthetic,
Silkolene and Motul both state on their bottles label if Ester is in the oil.

I now use real fully synthetic, see Silkolene Pro 4 Plus below which I highly recommend.

I highly recommend you at least use real semi synthetic oil, since mineral oil is not good enough for the Honda CG125 engine in my opinion.
Due to the average engine revs (rpm) are much higher than a larger engine,
small quantity of oil in engine (most larger engines hold around 3 to 4 times more oil), and many other things.

I would only use motorcycle oil, car oil might work but might cause trouble in the long term.
There are so many technical reasons why not to use car oil, the main ones are cars do not use the engine oil in the clutch or gearbox..
For instance motorcycle oil and car oil should have a API rating on them, motorcycle oil stops at SJ, but the best car oil currently goes on to SL.
The best car oil has anti friction chemicals in that will probably result in the clutch slipping (that is bad) on a motorcycle,
that's because cars do not use the engine oil to lubricate the clutch unlike nearly all motorcycles.
Engine oil is not really meant to be used in gearboxes, but in motorcycles it nearly always is (unlike cars), this means the oil has a much harder job and life.

I would not use a very cheap or unknown brand of motorcycle oil, since it could clog up the centrifugal oil filter and or even damage the engine.

I now use Silkolene Pro 4 Plus 5W-40 Fully Synthetic oil (after using Silkolene Comp 4 for a long time).
The 5W means the oil will be thinner when engine is cold (so engine will be better protected and lubricated).

The engine has around 1/3 less vibration at the top of the rev range (this is really good for engine and rider).
The clutch is much better, overheating and varying far less (especially around town racing between the lights)
and has better traction (friction).
Gearbox is also changing much better (this will be linked to the clutch since it's not overheating so much),
it even clunks far less severely when you change down at to higher road speed.
Engine is much quieter and might be revving slightly more freely as well.

All the above happened the first time I put Silkolene Pro 4 Plus oil in to the bike,
Honda CG125 oil changes normally leave 20% of the old oil in the bike, so I was not running 100% new oil.
When it was time to change the oil, I tried to warm the engine up far more than with the Silkolene Comp 4 oil.
I did 50 miles at high engine revs with a 30 min rest at half distance.
To my amazement the oil drain nut and the oil was substantially cooler than with the Silkolene Comp 4 oil.
There is a slight chance this was due to a strong cold wind, but I do not think so.
I think its much cooler because its lubricating and cooling the engine better (explains the other improvements).

The oil change also brought out a layer of very thick black oil and a little metal (very little) from the engine.
This is a really good thing, it means the oil is doing a better job of picking up the thick black oil and metal
that builds up at the bottom of the engine and gets it out of the engine.
After the oil change everything has improved again due to there is far more Silkolene Pro 4 Plus in the engine.

I am amazed by these results,
I do not think the Silkolene Comp 4 is a bad oil, I think it's probably a very good oil for the price,
but my Honda CG125 front disc brake model obviously needs all the help it can get,
with oil quality due to low quality components (compared to expensive bikes).

From these results, I think my engine, clutch and gearbox are being much better protected with the Silkolene Pro 4 Plus oil,
so I really recommend you try it.
Especially if your CG125 spends a lot of time at high engine revs or a lot of short journeys (since its thinner when cold = better lubrication = less engine wear).
Silkolene Pro 4 Plus 5W-40 costs less than £4 more than Silkolene Comp 4,
so why not try it and see what you think.

I plan to continue using the Silkolene Pro 4 Plus in my engine and will continue to examine the oil that comes out of the engine to see how well its cleaning.
I will continue to publish my results in this section (so this review is a continuing long term test).
Another good thing about Silkolene Pro 4 is its amber in colour (light yellow),
this means its easier to see it darken as it gets dirtier in the engine due to burning deposits etc.
Silkolene Comp 4 is brown so is harder to see the change.

3rd Oil Change with Silkolene Pro 4 Plus (removing the Pro 4 plus for the 2nd time from engine).
I tried to warm engine up with a 100 mile ride at high revs with a 1 hr stop at half distance, the oil nut was about as cool as last time (50 mile ride).
There was no thick black oil this time, just a very small amount of black oil at the bottom (so the previous oil change really did a large amount of cleaning).
Looking at the oil I did get out, it was still a bit dark for my liking, so I expect its still cleaning the engine out, so next time I expect it to be lighter.

A lot of shops and mechanics believe (they are wrong) that if you use fully synthetic motorcycle oil in motorcycles with normal clutches you may / will get clutch slip.
They also often think (they are wrong) you should not go to fully synthetic motorcycle oil and then down to semi synthetic or mineral oil since it might cause trouble.
They may also believe (they are wrong) that you should not mix semi synthetic with fully synthetic or mineral oil (when you change oil you do not get all the oil out).
These shops and mechanics have based their beliefs on myths and hearsay (as well as tests using car fully synthetic oil in motorcycles).
The truth is known by the motorcycle oil scientists who work, design and test the oils on motorcycles (I managed to speak to one).
I even found out that mixing different brands of oil is probably ok (can not be guaranteed but should be ok).

If you want an explanation about oil and what is and what is not real semi or full synthetic and why you would want it,
I will need to be more precise.
Mineral oil comes out of the ground.
Synthetic is supposed to be 100% man made.
One company messed around with mineral oil and claimed that since a person messed about with it, it was now semi synthetic,
there was a legal case and they won.
All they did to the mineral oil was molecularly convert it.
Based on that principle you could milk a cow and boil the milk and claim its now semi synthetic.

There are two 100% man made products and they are real synthetics, since they are nothing to do with mineral oil.
One is Ester, this is what protects your engine when cold and also at high revs.
The other synthetic product is PAO
Ester clings to the parts in the engine and lubricates them,
Mineral oil does not cling as well when the engine is cold, this results in a lack of oil lubricating the engine,
which is why most engine wear happens when the engine is cold.
Mineral oil also loses its viscosity (thickness) at high temperatures, so when you are at high engine revs, the oil thins and loses its lubrication abilities,
mineral oil also breaks down at high temperatures so must be replaced more often.
Ester must be mixed with PAO or Mineral oil, else your engine would smash itself to pieces.
PAO when mixed with Ester results in the ultimate oil (better than Mineral oil with Ester in it),
but PAO on its own is worse than mineral oil on its own.
Real Fully Synthetic oil should have Ester and PAO in it with no Mineral Oil (or any form of converted mineral oil).
Real Semi Synthetic oil should have Ester with some form of Mineral Oil in it.

I have tried to find as many brands and models of motorcycle oil as I can in the UK and work out what's in it.
Finding out what's in the oil has proved to be impossible in nearly every make.
Even when it says fully synthetic it could be 100% messed about with mineral oil (which may give less protection than normal mineral oil).
Or could be 100% PAO with no Ester in it.
Semi Synthetic as mentioned before also means nothing.
There are loads of names that oil companies have invented to make their oil sound like its better than others, that actually mean nothing.
PAO, Ester and Mineral oil are the only names that mean anything, they are scientific facts.

Ester costs a lot more to manufacture than PAO, so some oil companies are tempted to make a PAO only oil with no Ester in it.

The only makes of motorcycle oil I could find in the UK that states on the bottles label if Ester is in their oil is Silkolene and Motul.
I believe Silkolene Pro 4 Plus is PAO and Ester with no form of Mineral oil in it.
I expect Motul 300V is the same.
I believe Silkolene Comp 4 is Mineral oil and Ester.

I personally would not trust any make that does not state if Ester is in the oil.
Even if the manufacturer has a reputation for being very high quality and expensive, you are relying on trust and they can easily re label someone else's product.

Centrifugal Oil filter
The centrifugal oil filter should not need to be touched as long as the engine oil has been changed at the correct mileage or before (see Oil change above).
But some people change the oil every 5000 miles or never, this means the oil becomes very dirty, the filters then become clogged up and need to be cleaned.
When the oil gets dirty you will notice the colour change (goes darker and darker until it goes black when very dirty) and other things,
if you change the oil at the correct mileage or before (see Oil change above), the oil you drain out should be similar or identical in colour to the new oil.
Different brands and models of oil can have different colours, the colour will look lighter when you pour it compared to looking at it in a container.
For example the new oil may look light brown as you pour it but look black when its in a container.
Most if not all mechanics never clean the Centrifugal Oil filter, including the Honda ones, unless it has clogged up due to lack of oil changes.

If you have neglected the oil changes and the oil has turned very dark or black, you maybe able to clean things without doing anything except,
change the oil far more frequently than normal until the oil you take out is much cleaner,
you can also use an oil with more powerful cleaning abilities (see Silkolene Pro 4 Plus review in the Which Oil quality to use section above).

But the methods above will only work if things are not to bad and may or may not clean things enough.
Even if you or a mechanic clean the centrifugal filter as mentioned below,
I still advise you do the things in the paragraph above to clean everything as much as possible, ideally do them before and after cleaning the centrifugal filter.

The Owner's Manual for the front disc brake model claims the Centrifugal Oil filter should be cleaned every 7500 miles, but the advice is to ignore it.

If the Centrifugal Oil filter has clogged up due to lack of oil changes, you will have to clean it or pay a mechanic.
Unless you are good mechanically or have a Haynes or other Honda CG125 workshop manual, do not try it yourself.
You need a special tool to remove it, the specifications of the tool can be obtained and manufactured at most motorcycle servicing shops.
The tool required may depend on the model of Honda CG125.
The Haynes Workshop manual for the Honda CG125 should tell you and may even tell you how to make the tool yourself.

You also have to remove the oil, clutch cable, exhaust, foot rests including the metal bar they are on, brake pedal?
If you have a kickstart, you have to remove that as well.
Remove the right hand side engine cover, gasket (may need to buy a new one), oil filter cover.
You then have to stop the engine from turning (put bike in gear and apply rear brake).
Then you can unscrew and remove the filter.

Servicing

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