GN250 - 300cc upgrade?

[jake47]

hi I have a suzuki gn250cc c 1992 , and have ordered a big bore kit from e bay from a chinese seller here http://cgi.ebay.co.uk/GN300-GN250-BIG-BORE-cylinder-Improve-performance_W0QQitemZ270514614149QQcmdZViewItemQQp tZUK_Motorcycle_Parts?hash=item3efbed6f85 as you can see it states it ups the power to 300 cc.As ime not too used to working on bikes , well for some years anyway i wonder if anyone else has used the above and what are your thoughts.
is it going to be fairly straightforward to do the job or is it going to be a bike mechanic ? as cost is important i would like to have an attempt at doing the job myself but am a bit wary, could this kit do permanent damage and if so i suppose i could replace it with the original bore and piston etc.What do you think?

http://www.bikechatforums.com/viewtopic.php?t=189648

[CookMySock]

That looks like a piece of piss. If you think you can do it, you probably can. You're only unbolting three or four things and basically bolting them back on.

Check the ring gap by fitting them in the cylinder.
Be careful fitting the rings to the piston - they kink easily.
Check whether the piston has a front or back, and that you put it the right way around.
When you fit the piston pin, take care to oil it up first and slide it in gently and not rack it.
Find some detailed instructions for tightening the cylinder head bolts.
Use a torque wrench for everything. Yes, everything, or you will strip something.

Be careful with timing the camshaft. Before removing the cam, put the engine exactly on TDC on its firing stroke and don't bump it. Take a photo of the camshaft, and mark the cam and the chain with a white paint marker. Don't let the chain fall slack and drop into the engine.

Do the whole operation in one hit - don't spread it out over a week or you won't remember where things went.

Make notes and take pics.

Don't thrash it for the first 20 mins of riding it, while it beds its' rings in.

Have fun! Working on bikes IS fun! POST PICS HERE AFTER YOU ARE DONE so we can drool over your hot GN. :lol:

Steve

[R6_kid]

It doesn't up the power to 300cc, it increases the capacity (displacement) of the engine.

$300NZD + shipping is a lot of money to get a 3hp gain.

[The Everlasting]

It doesn't up the power to 300cc, it increases the capacity (displacement) of the engine.

$300NZD + shipping is a lot of money to get a 3hp gain.


Hell yeah,maybe if you want more power,you might want to look at getting a different bike..?

[F5 Dave]

Well clearly it would make the bike non learner legal (in NZ at least, see you're in UK) but likely the Chinese quality will bite you, but more so will overpower the chassis which it is already ill-equipped to deal with the original wheezy say 18hp engine.

[The Everlasting]

^How would they know he has increased the capacity of the engine? I'm guessing it doesn't look any different etc...

[quickbuck]

^How would they know he has increased the capacity of the engine? I'm guessing it doesn't look any different etc...

Doesn't matter. no 250 law in UK

[The Everlasting]

Doesn't matter. no 250 law in UK


Oh i see,so any learner can go out and get themselves a 180hp superbike and then kill themselves....

:doh:

[Scotty595]

Oh i see,so any learner can go out and get themselves a 180hp superbike and then kill themselves....

:doh:

I believe they are limited to 15HP for a learner and then it gets progessivly bigger as you move on. Much better than NZ's system IMO where you can get on a 70HP aprilia RS250 for a first bike :S

[CookMySock]

I wonder if you can legally turbocharge a 250cc learner bike in NZ.

Steve

[hayd3n]

I wonder if you can legally turbocharge a 250cc learner bike in NZ.

Steve

probably
bbut would the l plate stay on for long?>

[quickbuck]

I believe they are limited to 15HP for a learner and then it gets progessivly bigger as you move on. Much better than NZ's system IMO where you can get on a 70HP aprilia RS250 for a first bike :S
This is what I believe too....


I wonder if you can legally turbocharge a 250cc learner bike in NZ.

Steve
Of course you can....

What do you think the expansion chambers on a two stroke actually do???

As for a Turbo 4 Stroke, there is nothing to say you can't.
It is much easier just to buy and ride a 400 though.

[hayd3n]

the rest of a new gn is chinese built anyway

[CookMySock]

As for a Turbo 4 Stroke, there is nothing to say you can't.Well that is very curious. And not hard to biff a plate under the cylinder to lower its compression... Thats got me thinking.. :cool:

Steve

[jake47]

It doesn't up the power to 300cc, it increases the capacity (displacement) of the engine.

$300NZD + shipping is a lot of money to get a 3hp gain.


Hi the shipping is £30 which is about 66nz dollars, and the hp gain is 15.5kw=20.77Hp to 19kw=25.4 a difference of 4.6hp if the figures are to be believed.i was interested that someoe here said the gn's are made in china ,didnt know that.
As the bike is 1992 and original peformance had dropped i havent checked the compression but the top speed is well below the 85mph shown here http://www.classicmotorcycles.org.uk/classicbikes/cb_suzuki_gn250.htm like maybe 75mph now , i thought maybe it would be worthwhile giving it a go.As to the quality of the bits ime not sure if thers going to be ok or will fall apart , at least if they do i will have the original pistons etc.With regard to the learner laws i have a full licence and could ride any capacity cc after returning to biking after a number of years and chose the gn250 because it was cheap to tax and run etc ,.Anyway one other thing would the carb need to be adjusted??/ Thanks kiwi bikers for all your replies , i will let you know of the outcome whenever i get the parts and a bit of nice weather to do the job (lots of snow at he moment haha.byeeeeeee

[The Everlasting]

I believe they are limited to 15HP for a learner and then it gets progessivly bigger as you move on. Much better than NZ's system IMO where you can get on a 70HP aprilia RS250 for a first bike :S

Oh okay,i thought they had no restrictions...:lol:

Yeah their system sounds better and safer.

[imdying]

What do you think the expansion chambers on a two stroke actually do???I think a better question would be what do you think a two stroke expansion chamber actually does??

[hmmmnz]

give it a go, a cast iron barrel is a cast iron barrel,
i dare say the piston and rings are probably sub standard, but if you keep all the original gear, if it goes tits up,
then well just stick all the original stuff back on

good luck

[quickbuck]

I think a better question would be what do you think a two stroke expansion chamber actually does??

Well, could tell you, but it would be a thread hijack... Besides which, Google is still there.... Just, by the sound of it!

[quickbuck]

Okay,
Bugger it.... Hijack alert.......


You know that changing the exhaust pipes on your two-stroke motorcycle can have a marked effect on the engine's power characteristics, but do you know why?

Simply put, it's because the two-stroke exhaust system, commonly referred to as an 'expansion chamber' uses pressure waves emanating from the combustion chamber to effectively supercharge your cylinder.

In reality, expansion chambers are built to harness sound waves (created in the combustion process) to first suck the cylinder clean of spent gasses--and in the process, drawing fresh air/gas mixture (known as 'charge') into the chamber itself--and then stuff all the charge back into the cylinder, filling it to greater pressures than could be achieved by simply venting the exhaust port into the open atmosphere. This phenomenon was first discovered in the 1950s by Walter Kaaden, who was working at the East German company MZ. Kaaden understood that there was power in the sound waves coming from the exhaust system, and opened up a whole new field in two-stroke theory and tuning.


More can be found HERE (http://www.motorcycle.com/how-to/how-twostroke-expansion-chambers-work-and-why-you-should-care-3423.html)

[imdying]

Yeah, that's basically wrong (the metaphor), but I suspected that you'd run across something like that.

Even if it weren't, it has no relevancy to DB's post in any case.

[quickbuck]

Yeah, that's basically wrong (the metaphor), but I suspected that you'd run across something like that.

Even if it weren't, it has no relevancy to DB's post in any case.

So you have a better explination??? And there are actually different explinations as to why strokers "come on Pipe"?

You do realise bolkting a Turbo to an engine is classified as Supercharging as well, don't you?

[SS90]

So you have a better explination??? And there are actually different explinations as to why strokers "come on Pipe"?

You do realise bolkting a Turbo to an engine is classified as Supercharging as well, don't you?

The thing is quickbuck, that a "supercharging effect" does not constitute "supercharging" (anymore than a "forced air" air box does)

There is a lot of rubbish written on the internet about 2 strokes (and like many things, the same rubbish gets repeated time after time), just by different people.

I assure you that an expansion chamber does not "supercharge" a cylinder (super charging "effect" not withstanding)

I am of the opinion that the first person to write of the "supercharging EFFECT" (in English literature) was AG Bell, when he reffered to this "super charging effect", and many people (mistakingly) took this to read that a two stroke with an expansion chamber was "super charged".

The fact is, that it isn't.

I am not alone in thinking this.

The FIM certainly don't think a 2 stroke is supercharged...... they banned supercharging quite some time ago.

An expansion chamber is a busy piece of kit, and indeed we can use the resonance to do many things that assist evacuation of the crankcase ( crankcase scavenging), as well as plugging the exhaust port, after pushing back (some) of the over scavenged charge,(which is part of the cylinder scavenging phase) and in the case of a reed valve inlet, hold the top reed open to operate the inlet boost port. (Using the negative vacum created in the header after the returning pulse wave)

Among other things.

[imdying]

So you have a better explination???I don't need one, why don't we just stick with the facts, they're out there if you choose to look for them.

And there are actually different explinations as to why strokers "come on Pipe"?No, there is only one reason. But back to your original post, there is no compressor in an expansion chamger, and thus no 'charger' of any sort. Utilising pressure waves in an expansion chamber is not supercharging, turbo charging, or any other form of charging. The guys metaphor is crap, he would have been better to just stick with the facts.


You do realise bolkting a Turbo to an engine is classified as Supercharging as well, don't you?Although it's an irrelevant straw man, turbocharging is a sub category of supercharging, but nobody refers to them as such as it strips the clarity that the two seperate terms give.

[Mikkel]

Naturally aspirated: the pressure on the intake side of the engine is, roughly, equal to atmospheric pressure. I put in roughly since a slight overpressure may be present due to clever intake designs and such.

Forced induction (turbos and superchargers): the pressure on the intake side of the engine is significantly higher than atmospheric pressure due to a compressor - driven either mechanically or by the exhaust gasses.

On two-stroke engines it becomes a bit muddy compared to four-strokes, since the air/fuel mixture is effectively being "forced" into the combustion chamber by the piston's downward stroke - i.e. it isn't only being sucked into the cylinder.
However, unless there is a compressor compacting the mixture the overall gas density will be equivalent to atmospheric pressure. This has to be the case since the piston displaces an equal volume inside the cylinder irrespective of direction of travel.


Oh, and a GN250 isn't a sportbike...

[imdying]

Want to muddy it even further... so called 'chemical supercharging' ala NOS... no compressor again, but more oxygen added that can be obtained from atmospheric pressure alone.

[Mikkel]

Want to muddy it even further... so called 'chemical supercharging' ala NOS... no compressor again, but more oxygen added that can be obtained from atmospheric pressure alone.

Yes, but I wouldn't ever call it supercharging. After all, the pressure remains roughly at atmosphere. http://en.wikipedia.org/wiki/Nitrous_oxide#Internal_combustion_engine

It would be just as valid to consider adding stuff to the fuel supercharging. I.e. not at all, IMO.

[imdying]

Agreed, same end result != same thing.

[quickbuck]

......there is no compressor in an expansion chamger...................

.

Okay, SS90 has given a pretty good rundown...
But, there is NO compressor?? Apart from a sound wave!

[nodrog]

Hi the shipping is £30 which is about 66nz dollars, and the hp gain is 15.5kw=20.77Hp to 19kw=25.4 a difference of 4.6hp if the figures are to be believed.i was interested that someoe here said the gn's are made in china ,didnt know that.
As the bike is 1992 and original peformance had dropped i havent checked the compression but the top speed is well below the 85mph shown here http://www.classicmotorcycles.org.uk/classicbikes/cb_suzuki_gn250.htm like maybe 75mph now , i thought maybe it would be worthwhile giving it a go.As to the quality of the bits ime not sure if thers going to be ok or will fall apart , at least if they do i will have the original pistons etc.With regard to the learner laws i have a full licence and could ride any capacity cc after returning to biking after a number of years and chose the gn250 because it was cheap to tax and run etc ,.Anyway one other thing would the carb need to be adjusted??/ Thanks kiwi bikers for all your replies , i will let you know of the outcome whenever i get the parts and a bit of nice weather to do the job (lots of snow at he moment haha.byeeeeeee

dont you have any friends in England to ask? you're not related to Skidmark are you?

[SS90]

But, there is NO compressor?? Apart from a sound wave!

That is correct.

That allows for a super charging "effect", but does not "super charge"

No more than a forced air air box super charges.

[jake47]

dont you have any friends in England to ask? you're not related to Skidmark are you?


Yep loads of friends thanks but none with any knowlege of suzuki gn 250's .But thats not surprising as there arnt too many of them over here but i believe they where still made for the NZ market until recently? and there are a lots more on the road.
btw never heard of skidmark.

[Lucy]

the rest of a new gn is chinese built anyway

I'm pretty sure a '92 will be Japanese made.

[jasonu]

You are wasting your time and money

[Sable]

You are wasting your time and money
In a big way.

[SS90]

Don't take it the wrong way Jason, because this is not intended as a personal insult, I know how much work would go into your bucket, but erm, aren't you asking 5K for yours?

The same could be spent purchasing a 95 RS125, and at the end of the day, your bucket will never handle as good as an RS125 (even an early one)......... SOME would say 5K on a bucket is a waste of money, personally I would never spend 5K on a bucket, but it is a bit rich to say this dude is "wasting his time and money", would his money be better spent on your 5K bucket?, (which , by the way will never be a match for an old RS125 framed bucket), I think the guy should go for it.........

[jake47]

Don't take it the wrong way Jason, because this is not intended as a personal insult, I know how much work would go into your bucket, but erm, aren't you asking 5K for yours?

The same could be spent purchasing a 95 RS125, and at the end of the day, your bucket will never handle as good as an RS125 (even an early one)......... SOME would say 5K on a bucket is a waste of money, personally I would never spend 5K on a bucket, but it is a bit rich to say this dude is "wasting his time and money", would his money be better spent on your 5K bucket?, (which , by the way will never be a match for an old RS125 framed bucket), I think the guy should go for it.........

Thanks ss90 well it seems to have gone in ok and no probs with the timing or carbs, as ime taking it gently at the moment its early days .So fingers crossed and i will keep you all posted.:mellow:

[gorgonzola]

Hi community.

If someone is looking for gn250/TU250 parts look here:
gn250_taobao_com. Taobao is the daughter company of alibaba_com.
There are ignition coils, carburetors, CDIs, mechanical parts
Prices are in Yuan.

Gn125 is GS125 there.

You can search with gn250 as a search word. There are two GN250
shops but one seller doesn't communicate in english.

Seller is Xietoo. He is able to communicate in english.
If someone is interested I give you his email.
Some of his parts are SGP parts from japan.
I just ordered the mitsubishi ignition coil from him.
This is the origional Gn250 Japan ignition coil.
It is the same coil as on my 1989 gn250.


Taobao is the chinese domestic C2C platform. The language is chinese.
Eventually you need the simsun font to be able to display
the website.

Chinese GN300ccm cylinder upgrade set:
item_taobao_com/item.htm?id=7017406180

Including shipping costs to europe approx. 120€.
Weight is 4Kg including packaging.

Manufacturer of the GN250/WJ250GY is wonjan motors
www_wonjan_cn
If my memory serves me well the GN250 factory was sold in 2000 from Japan to China.
Wonjan manufactures 1.5 million bikes each year.

Someone here wrote:
"I understand (and someone will be sure to correct me if I'm wrong) that you can tell by a quick glance if your GN is made in China - the Japanese ones have spoked wheels and the Chinese ones have those alloy-type wheels."

I think it is wrong. I own two versions spoked wheels and aluminum wheels and they both are made in japan I think. So the chinese Gn250 should start around the year 2000.

Wonjan has changed the website. This information was there.
But I can ask xietoo. His Hobby is: GN250

The Gn300ccm upgrade works. The chinese guys recommend a different carburetor from Keihin. There are 2 ptk carburetors from www_ptk_cn or com , one is more for the GN250
and the other is more for the GN300 version but you can use the 300ccm cylinder with the
origional mikuni bs34ss carburetor.

Ptk is the chinese daughter company of the japanese carburetor manufacturer teikei.
There are new ones starting from 280yuan.

But I agree the 300ccm upgrade is almost a waste of resources.
At least one guy with a sidecar GN250 model tried it.


I think a GS500E is a better option or anything else if you want more power.



Regards.
gorgonzola