Honda CG125 Increasing Engine size
How to Increase Engine size
How to Increase Engine Size
History of the Engine
http://world.honda.com/history/challenge/1975cg125/index.html
The Honda CG125 is 124cc in engine size.
Its a Overhead Valve design (push rod).
http://en.wikipedia.org/wiki/Pushrod
Its basically a Honda CB125 engine, except it is Overhead Valve instead of
Overhead Cam.
http://en.wikipedia.org/wiki/Overhead_cam
A Overhead Cam is more complicated and needs more servicing (servicing is
critical) but gives better engine performance.
The Overhead Valve system is needed for the third world, who demanded easy
servicing (also survive if engine never serviced), easy to repair and cheap.
The Honda CB125 and Honda CG125 engines are used in other Honda motorcycles.
As a general rule, as long as its a Honda Motorcycle (not sure about scooters),
4 stroke, Air Cooled (not liquid cooled) & single cylinder,
if it says overhead valve (OHV) its the CG125 engine, if it says overhead cam
(OHC) its the CB125.
The 125cc engine size history is complicated, a long time ago the learner laws
of the UK and several other countries was 250cc.
250cc engines over time increased in power output, until they were to powerful
for the UK and the several other countries,
so they changed the law to 125cc.
Back then 125cc was a uncommon size, but due to the law, 125cc engines became
common in the countries with the 125cc learner law.
In countries without the learner law, 125cc has never caught on (except third
world countries that use whatever is cheapest).
Before the 125cc learner law 150cc was common.
Engine manufacturers hate to build and design new engines, so they normally just
convert the engine to the size required.
Reducing the engine size is the easiest and safest since the engine will have
less power, this means less strain on all the other components of the engine and
bike.
All you have to do to reduce the engine size, is put a sleeve or larger sleeve
in the cylinder and change the piston to a smaller one.
You can also change the crank so the piston does not move as far up and down the
cylinder (called the Stroke).
Manufacturers often increase the engine size above the original design of the
engine and this normally has side effects.
The side effects often include, increased vibration and components not lasting
as long (they may change or improve some components to compensate).
To increase the engine size you need to bore out the cylinder (barrel) or change
the sleeve or change the cylinder (the size is called the Bore).
Sometimes they are able to change the crank so the piston moves further up and
down the cylinder (called the Stroke).
All Honda CG125 & Honda CB125 engines have always been
Bore x Stroke 56.5 x 49.5 mm
I then wondered if there was a Honda CB150 in the past and found there was, the
Honda CB125 maybe a converted Honda CB150.
That made me wonder if there are still Honda CB or CG150 being made today, this
is what I have found.
In brazil http://www.honda.com.br/
(Portuguese language) were the latest Honda CG125 are made,
they also put a 150cc Overhead Cam engine in developing just over 13hp (125cc =
11hp).
Its Bore x Stroke is 57.3 x 57.8 mm, 149.2 cc, 9.5 :1 compression, peak power
8000 rpm, peak torque 6500 rpm.
http://www.honda.com.br/web/index.asp?pp=motos&ps=especif&id=16
The Honda CG125 for brazil is below
http://www.honda.com.br/web/index.asp?pp=motos&ps=especif&id=66
Engine performance is not only about power output.
You also need to look at the torque output, this is the amount of pulling power,
very important when going up hill or head wind or heavy loads.
The larger the engine size the more torque output you will get.
You also want to look at the state of tune, you can tune a engine to give
maximum power output (high state of tune),
but the engine will only produce that power at the top of the rev range and
below that the power and torque output will be very low.
The Honda CG125 is in a low state of tune, this means the maximum power output
is low,
but that means you will get far more power and torque in the low to mid range of
the rev band than a 125cc engine in a high state of tune.
India
http://www.honda2wheelersindia.com/ has started making the next generation
of Honda third world bikes (Honda CG125 is the current),
its first is the Unicorn
http://www.honda2wheelersindia.com/unicorn/flying_machine/about_unicorn.asp
Its a bit heavy, but notice the monoshock suspension, fuel economy we can only
dream of, Overhead Cam, 150cc engine etc..
It looks like its called a Honda CBF150 in other countries.
The engine may or may not be totally different to the Honda CG and CB engines.
India has also released a Honda CBF125 called the Stunner (in 2008), it has a
Overhead Cam.
http://www.honda2wheelersindia.com/products/stunnerCBF/2008/
For the European market (2009 onwards) the Honda CBF125 carburettor has been
replaced with fuel injection to make it pass the Euro 3 emission law.
The Honda CBF125 Bore and Stroke is 52.4 x 57.8mm which is totally different
sizes to the CG125 and CB125 engines.
The Honda CBF125 engine may or may not be a totally different engine to the
CG125 and CB125 engines.
But notice the Honda CBF125 Stroke is identical to the Honda CG150 mentioned
above.
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