New guy - possible bike?

[adengel]

Hi, I am contemplating having a crack at this, although will be a mobile road block I am sure. Is a Honda CG125 suitable for getting started? Just that it would cost a few $100 instead of a few thousand - in case I dont find it to be my thing? Any advice appreciated - Cheers

[speedpro]

perfect bike to get started. Spencer still has his, after 20 years or so!!

If it doesn't work for you I'll take it off your hands for my boy. Don't get put off by the pushrod bit as it isn't really a handicap. Buy it and bring it to the track for a play.

[speedpro]

Just noticed, bit far to go if you don't like it.

[adengel]

Thanks for that - I was going to dive straight in and get an FXR but it would probably be beyond my skills and wallet. Used to putt about on a CG110 when younger so think this might be the go

[kel]

Dont be afraid of the FXR you will probably save money in the long run and it'll be a more enjoyable experience i.e. less mods required, better handling etc etc. My FXR has only cost a mere :shit: Maybe the CG isnt such a bad idea.

[timg]

Hey! Welcome. Your CG would be a low $ start. I started of a standard CB125t, got hooked and got a FXR. Great fun. Check out http://www.bmrc.co.nz/ & www.fxr150.co.nz (http://www.fxr150.co.nz) for all you need to know. Pop out to Ruapuna or Levels and have a chat and look around. The bucket folks are a friendly bunch and happy to help and point you in the right direction. There's a meeting at Levels this Saturday and at Ruapuna on the 9th & 10th Oct. Look forward to seeing you out there sometime. Cheers.

[adengel]

Thanks for all the feedback - I will definately pop out to Ruapuna for the next meet and have a look around. The CG I was looking at went for more than I was expecting - so perhaps an FXR or CBR isnt such a bad investment as you say and I guess yu have a fair chance of getting most of it back should you move on. Really looking forward to having a look, i ride a Harley Electra Glide Standard (yeah yeah I know a boat anchor! but i enjoy touring) so this racing lark is going to be a totally new experience for me and ironically its on my bucket list to do!!!! :yes: Thanks again

[jasonu]

Buy the best bike you can afford!!!

[Muzzab]

It's addictive, you'll have fun on whatever you buy :yes:

[all4A50s]

Thanks for all the feedback - I will definately pop out to Ruapuna for the next meet and have a look around. The CG I was looking at went for more than I was expecting - so perhaps an FXR or CBR isnt such a bad investment as you say and I guess yu have a fair chance of getting most of it back should you move on. Really looking forward to having a look, i ride a Harley Electra Glide Standard (yeah yeah I know a boat anchor! but i enjoy touring) so this racing lark is going to be a totally new experience for me and ironically its on my bucket list to do!!!! :yes: Thanks again

There's a CBR125 recently on sale on TM, which would be worth having a look at. It would be great starting point and there's parts up the #$%& on line you can buy for them.

I race one and find it handles better than the FXR but doesn't quite have the straight speed (being 25cc smaller).

[Buckets4Me]

I race one and find it handles better than the FXR but doesn't quite have the straight speed (being 25cc smaller).

thats why they bore them out and put bigger pistons in them

[Buckets4Me]

thats why they bore them out and put bigger pistons in them

the other problem with the cb125t is the frount brake (go have a look )
aparently tzr250 frount ends fit on well

[richban]

I race one and find it handles better than the FXR but doesn't quite have the straight speed (being 25cc smaller).

They both have shit suspension. And both can be improved. The 125's are gutless compared to a standard FXR. The CBR 150s on the other hand can fly.

[Henk]

Rob Jones up here has a CBR125 frame with an FXR engine in it. Handling on the CBR is a bit better but the main reason I think is that he is a tall bugger and fits the Honda better. He ditched the CBR engine in favour of the FXR because he found the honda motor gutless compared.

[richban]

219369It would be interesting to see how a YZF-R 150 would go as a bucket. They have a really long stroke engine and I think the wheels are the right size. Nice size to. Yes I want one. Opps I mean the 125 bored out to 156.

[Arronduke]

I have a CG125 bucket...

Spent a few dollars on it and it goes very well.

Big Bore CG125 Engines
I first found out that it is possible to overbore and over stroke small Honda OHC engines from a website called Kaila.net/TL125.
From this website I found that it was possible to raise the cubic capacity of TL/CB125 engines to 150cc by increasing the bore to 61mm and to go further by
altering the crank to get about 210cc.
Since the cg125 engine is similar to the OHC engines (But better because there is no cam chain and cam bearings to go wrong) I obtained cg125 top end to
overbore from a motorcycle scrapyard.

Options

piston Bore (mm) Liner Engine size CC Notes
CB550 58.5 Standard 134 Compression ratio about 7.5/1
CB750 61.0 CB550/CB750 146 Crankcase mouth needs opening 1mm
CBX550 58.5 Standard 134 Compression ratio about 9.5/1 (untried)
XL185 63 CB750 154.5 Low compression
All of the above pistons use a 15mm dia pin

As you can see from the above chart, the most sensible choice is the Honda cb550 or cbx550 route.
As the cg125 cast iron liner is only 71mm in outer diameter, boring out to 61mm or even 63mm leaves little in the way of metal behind and would probably fail.
The solution is to machine out the cg125 liner and press in a Honda 550 or750 liner coated with araldite, and then bore out to the correct bore for the piston.
According to Dave at PISTONBROKE (Dave does this sort of thing often) the mouth of the cg/cb125 crankcase needs opening by about 1mm to accommodate
the lower part of a cb750 liner, also by doing so risks breaking into an oil way on cg125 engines.

Pistons
The Honda cg125 piston has a 15mm gudgeon pin and a slightly domed crown, the CB550 also uses a 15mm gudgeon pin but the piston is flat toped and .5mm
smaller crown height meaning lower compression.
I have recently found out that Honda CBX550 pistons may have a domed crown thus making it a better option by keeping the compression ratio at about 9.5/1.
Higher compression means more power, but good fuel is needed.
Lower compression means slightly less power but poorer quality fuel works fine.
I decided to bore out to 58.75mm (all I could obtain from David Silver spares was a CB550 .25mm oversized piston kit)

How it was done
Because I work in an engineering factory I had the barrel bored out on an Dean Smith & Grace centre lathe.
A friend at work clamped the barrel in a four jaw lathe chuck, adjusted the jaws until the bore was true using a dial guage and bored it out to58.73mm.
Then using fine grade emory cloth, the tooling marks where polished out taking the bore size out to the desired 58.75mm.
The cylinder head was cleaned and the intake and exhaust passageways polished using a dremmel type rotary tool.
The valves where reground in using grinding paste.
The barrel, piston and head was fitted on to the engine using standard gaskets.

Teething Problems
I started first time but ran rough until I sorted out the carb.
The carburettor needle has 3 grooves with the circlip fitted to the middle one; I found that if I moved the circlip to the top groove the engine worked well.

Performance
I have found that there is a noticeable increase in power as the bike can climb hills better and where as before it would only do 55mph on the flat (I am quite heavy)
I now can get 63mph. A lighter rider may perhaps get 68-70mph but that would be quite scary on my 1978 cb100n with cg125 engine.
I consider the modifications to have been worthwhile because I can maintain a higher average speed when riding the bike.
In America, according to the tl125 website, they bore out the crank pin holes then press in offset bushes to lengthen the stroke of the engine.
An aluminium thick washer is fitted between the barrel and crankcase mouth so that with the extra stroke the piston does not kiss the valves.
I don’t think this mod would make a reliable engine because a bush could come adrift and cause mechanical mayhem.
Someone else emailed me and says
The second line states the cast iron barrel is 71mm OD when its only 62.5mm OD measured from bottom of barrel.
The correct place to measure is at the bottom, not at the top.

There is a site where you can get CB550 pistons up to 1mm over size www.cmsnl.com page http://www.cmsnl.com/products/piston-25-repro_06132374000p/
This will then give you the choice of going up to 59.5mm, 3mm over size.
You can increase the compression by having the head ground or if you wish to keep your head standard, use the
head gasket off a W model (1998) onwards which all use a metal head gasket which is approx 0.5mm thinner.

I have 2 early cg engines 2 Brazil's, One W model, One M model, One ES4 engine.
All engines to M model (pre 2004) have 15mm gudgeon pin but the ES4 model (2004 on) has a 13mm gudgeon pin
The barrel (M and ES) (2001 onwards) has an oil way in the base, so you can not use an early barrel on these later engines.
Also the cylinder head has a different shape combustion chamber and will not fit on early models as the domed piston will hit the cylinder head.
2 oil way holes on the M model 2001 to date Picture
The new style flat top piston M model 2001 to date( please note 13mm gudgeon pin es4 models) Picture
The oil way in bottom of barrel M model 2001 to date Picture
The new style head reshaped to run with flat top piston M model 2001 to date Picture
Please note any engine mods can shorten engine life / if done wrong will break your engine.
Also note all pre 2004 models with drum front brake can be a bit lacking on stopping power,
even with new shoes and properly set up if you are in the 19 stone bracket.. It is like riding 2 up on the bike.

I'm in the lucky passion of having 3 cg125 and lots of spares.
To start with ill put an end to some of the myths 1976-80 approx models did not run bigger valve heads.
They did have a carb with a lot bigger slide which helped with performance at the cost of fuel if ridden flat out all the time. Fuel would drop to 75-80mpg.
The problem of doing a general guide of how to do mods and results is Honda over the years has changed air box intake size (more restrictive) and the jet sizes.
Slow running jet 36-40 Main jet 80-110, needle size and slide size.
Standard type carb, then carb with accelerator pump and back to standard carb for ES4 2004 model on.
The compression ratio also changes on years from 9:1-9.5:1.
The 1997-2003 W and M1 models had the most restrictive air box intake.

Mods done to my 1999 cg125 W model.

Cylinder head .010 ground off head, Head polished and ported, 1mm over size piston which gives you 128.5cc. Needle lifted up one notch on slide.
A little harder to kick over. I weigh in at 19 stone so a lighter rider of 12 stone would probably get higher speeds.
After running in the bore will do 70mph/75mph on flat so if we allow 10% for speedo error would be more realistic 63mph-68mph.
The reason for myself to improve performance was to get a bit more lower down power (torque) as my 25 mile travel is 30-40mph limits with a couple of 50mph.
As a result of mods I can go down to 20mph in top gear on flat and pull away up to 40mph at half throttle in approx 8-10 seconds.
With added bonus of 135mpg+ winter riding, in summer 145mpg and the best ever of 155mpg. The lowest was 115mpg giving it some right stick..
My carb has slow running jet 36 and main off 82.

Remember any modes to improve performance if ridden hard will shorten engine life and ruin your fuel economy.
You may find this article of interest http://vincentcrabtree.co.uk/XR200.aspx
Please note the Chinese clone Honda CG125 overbore and big bore kits will not fit on genuine Honda CG125 engines.
I have emailed a few Honda CG owners who were disappointed when they bought their kits and did not fit.

The reason the Chinese CG150cc kit does not fit is the liner is OD 67.5mm (to big) and the Honda CG crank cases are only OD 64mm (to small).
So to be made to fit would take full engine strip and major machine work to crank case, and the danger of breaking into one of the oil ways.
Remember this work will not be cheap and not all Honda Cg125 crank case will be able to be machined bigger.
Honda changed the design of crank case over the years.
Home

[Arronduke]

I did the above...

150cc
ground cam for more duration
GL145 pumper carb
XL100 5 speed gearbox

[Arronduke]

Oh and I did not write all that shit... if i did it would be full of spelling mistajes..:eek:

[Arronduke]

I will be looking for $600 notes when it comes time to sell.

only spent $600 to buy... plus $1500 on the motor
comes with spare engine and lots of bits
Shame your in CHCH.

[F5 Dave]

I did not really read much of that, 'cause it's about boring 4 stroke stuff:sleep:, but I would add there is a reason internet info can be misleading & this is a prime case in some instances.

CBX550 pistons would not be suitable in a CG or any 2 valve head bike. cuz they were 4V, unlike the CB550.

[Arronduke]

Dave,

You might be correct but I relined the CG and used a CB550 piston which was skimmed and then hand ground valve clearance in to the piston top usung clay to measure clearance.. took ages.

I have done the above mods and it works well.

Obviously you should stick to things with no valves...:bleh:

[adengel]

Wow thats a lot of info!! You guys are pretty serious! I didnt understand all of it as I am a mechanical Noob - one of the reasons buckets appeal - I can learn about that side of things whilst having fun - I got an 84 CG125E - do you know how to hardwire the ignition so I dont have to use a key? I have taken the battery out just want to be able to kick it over any time to start it without the key

[koba]

Wow thats a lot of info!! You guys are pretty serious! I didnt understand all of it as I am a mechanical Noob - one of the reasons buckets appeal - I can learn about that side of things whilst having fun - I got an 84 CG125E - do you know how to hardwire the ignition so I dont have to use a key? I have taken the battery out just want to be able to kick it over any time to start it without the key

Just do the mimimum required to get it out on the track and race the bastard!

[grantman]

Just do the mimimum required to get it out on the track and race the bastard!

I Agree with Koba

I just put petrol in mine :woohoo: