Motorcycle Owners Club

Honda CG125 but also some universal motorcycle information

Motorcycle Engine Oil

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Which Oil quality to use

Choosing the right oil is not only essential for the protection of any motorcycle engine,
but also to reduce wear, improve engine, clutch, gearbox and to clean.
This article will show you the differences between oil types, my reviews of the main types and disproves many of the oil myths.
As well as what real semi synthetic and real fully synthetic oil is and why not to always believe the claims on the oil bottles label.

I highly recommend you at least use real semi synthetic oil in any size of 4 stroke motorcycle engine
(2 stroke engines have nearly disappeared).
Since motorcycles from around the year 2000 onwards have gradually had stricter and stricter emission laws,
resulting in the engines running leaner and leaner and other problems (which generates more and more heat and other things).
As a result the oil quality has become far more critical (even in liquid cooled engines).

The above paragraph especially includes 125cc engines in my opinion.
Since 125cc average engine revs (rpm) are very high, small quantity of oil in engine and many other things.

I would only use motorcycle oil; car oil may 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.
Engine oil was never 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
(so motorcycle oil has extra things in it to protect the gearbox and increase the oil life).

The best car oil also 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.
The best car oil is fully synthetic,
using this oil in motorcycles is what probably started the using motorcycle fully synthetic oil will cause clutch slip myth.

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

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 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,
My motorcycles 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 it's much cooler because it's 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 improved again since there is a higher % of Silkolene Pro 4 Plus in the engine.

Another good thing about Silkolene Pro 4 Plus is it's amber in colour (light yellow),
this means it's easier to see it darken (on the dip stick) as it gets dirtier in the engine due to burning deposits etc.
Silkolene Comp 4 is brown so it's 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 hour 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 it's still cleaning the engine out, so next time I expect it to be lighter.

4th Oil Change, the oil I got out this time was cleaner (lighter) than the 3rd Oil Change but not massively better.

5th Oil Change, checked the clutch plates and centrifugal oil filter to disprove the myth about fully synthetic oil (see below);
both were perfect and did not need to be checked according to a very experienced mechanic.

From the results above, I believe my engine,
clutch and gearbox are being much better protected (less wear) with the Silkolene Pro 4 Plus oil,
so I highly recommend you try it (I will only use Silkolene Pro 4 Plus in my engine due to the results).
Especially if your bike spends a lot of time at high engine revs or a lot of short journeys
(since it's thinner when cold = better lubrication = less engine wear).

The bike used is a Honda CG125,
Air Cooled Push Rod engine (very primitive 4 stroke engine), with Euro II emission laws (2004 to 2008).
So if a very primitive engine design likes the very best oil,
which most people thought you only need for high end sports bikes, you can probably work out it's worth trying in your engine.

Silkolene Comp 4 (real semi synthetic) as proved above, is not as good as Silkolene Pro 4 Plus (real fully synthetic),
but it's cheaper and gives you much better protection than oils that claim to be semi synthetic
(when there not, see later on below for full explanation).
My advice is it really is worth trying Silkolene Pro 4 Plus, it may be more expensive but you get far more for your money,
in the unlikely event you do not find the improvements in your engine, gearbox and clutch worth the extra money,
just go down to Silkolene Comp 4.

Common myths about fully synthetic motorcycle oil, that many mechanics and shops still believe.
These myths have been around for many, many years, if confronted with have you actually experienced it or where is the proof,
all the mechanics / shops I have ever spoken to have no answer,
they often claim it makes sense for some reason or other or they heard or read about it.
To find out if these myths are true you need a motorcycle oil scientist who works,
designs and tests the oils on motorcycles (I managed to speak to one).

Motorcycle fully synthetic oil clutch slip myth has been proved to be wrong earlier on in this article
(car oil fully synthetic was probably used to create slip),
I have also proved it with my own tests, in fact Pro 4 Plus has less slip than non fully synthetic oil,
since Silkolene have admitted to putting a special additive in it,
after using the oil for many thousands of miles on the old original clutch plates (checking them after and finding them perfect)
and then many thousands of miles on new EBC clutch plates, I have absolutely no concerns with the oil.
The motorcycle oil scientist also confirms that motorcycle fully synthetic oil does not cause clutch slip, it's designed not to.

Next myth, you should not go to fully synthetic motorcycle oil and then down to semi synthetic or mineral oil or vice a versa
since it might cause trouble.
And you should not mix semi synthetic with fully synthetic or mineral oil
(when you change engine oil you never get all the old oil out).
All I can say about these myths is the logic behind them varies and every reason I have heard makes no scientific sense.
The motorcycle oil scientist also confirms the myths are wrong.
He even claims that mixing different brands of oil is probably ok (cannot be guaranteed but should be ok).

Below is a full explanation about what is real semi synthetic or real fully synthetic oil and why you would want it,
as well as why a bottle of oil may claim to be semi synthetic or fully synthetic when it's not.

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.
With that logic you could milk a cow and boil the milk and claim it's 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 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 it's 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.

When to change the Oil

The best advice is to treat the mileage in the Owner's Manual as an absolute maximum.

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 often results in the engine seizing,
the repair bill is normally so high, the engine has to be replaced with a new or 2nd hand one
(replacement engines are very expensive).
The other reason for burning oil is the engine is faulty or a part is worn out.

For example my Honda CG125 (front disc brake model) owner's manual says change the oil every 2500 miles.
After 1750 miles my bikes oil is still at maximum on the dip stick, but at 1950 miles it has dropped to half way.
So I should change the oil at 1750 miles or before,
if I was desperate I could instead,
top up the oil to the max mark (but would have to do this very regularly since oil has degraded and is being burned).
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 near identical to mine,
perfect engine and he starts burning oil at around 750 miles.

Just because no oil has been burned does not mean it's 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 black
(which is bad and bungs up filters, Honda CG125 see Centrifugal Oil filter),
even the oil on the dipstick will darken, see How to check the Oil level section below.

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.

It's 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 the Which Oil quality to use section above to find what Oil quality you should use.

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.

It's 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.

How to change the Oil

Honda CG125 only.
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 too 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 it's 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 too 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 socket will probably need a 1/2 inch ratchet not the normal one that's smaller),
you can also increase the leverage on the socket handle (ratchet)
by extending it with standard 22mm plumbing copper pipe from most DIY stores.

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, it's 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 you're worried show it to a mechanic,
it's 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 it has stopped dripping, or you cannot wait any longer,
put the filter back in, then the spring and finally the drain nut back on.
Make sure the nut still has a black rubber O ring on it or it's in the screw hole,
if not find it, you may have dropped it in the oil container when you removed the nut.
If you use a socket to tighten the nut, do not over tighten it, especially if you have a long handle,
the nut is soft aluminium and it's tighter when you try to undo it.

Pour 900ml (1 litre bottles often have marks down the side) of 10W/40 new engine oil (see Which Oil quality to use above) in,
Check the oil level is at the max mark or above (see How to check the Oil level above),
if it's below the max mark put more oil in until it's 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 it has 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.

Centrifugal Oil filter

Honda CG125 only.
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 it's 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 may be 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 too bad and may or may not clean things enough.
Even if you or a mechanic cleans 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.

My bikes oil changes are never neglected, at 25,000 miles the Centrifugal filter was checked and there was so little in it,
it's hardly worth mentioning.
A mechanic told me he has seen one which was full of metal debris,
from the clutch exploding due to deliberate, very, extreme abuse (probably repeated).

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 to be cleaned, you will probably have to 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 kick-start, 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.

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