Engine Swap???

[beccagz250]

I have a 250 as you already know, I want to put a bigger engine in it to make is faster. How would I do this, Can I use any motorcycle engine, or does it have to be a certain kind?? and Where can I buy a good engine from?? :??:

[celesboy1]

Originally Posted by beccagz250

I have a 250 as you already know, I want to put a bigger engine in it to make is faster. How would I do this, Can I use any motorcycle engine, or does it have to be a certain kind?? and Where can I buy a good engine from?? :??:

just do boreup / strokeup / both ways....its not easy thing to do by ourself....but with certain skill and passion...YES it works

[Water Warrior 2]

Originally Posted by celesboy1

just do boreup / strokeup / both ways....its not easy thing to do by ourself....but with certain skill and passion...YES it works

How much increase in cc's will you get with a bore n stroke job?

[celesboy1]

Originally Posted by Water Warrior 2

How much increase in cc's will you get with a bore n stroke job?

Several of my friend do boreup with
76mm piston (originally piston of daihatsu zebra)...about 275cc
78mm piston (originally piston of KIA sephia) about...300cc
Both of piston above has same stroke pin diameter with GZ so its make modding job easier

1.buy one of piston above
2.bring cylinder block to garage that have honing machine etc....
3.buy new diesel boring and process till its have same inner diameter with our new big piston
4.reshape edge of dome head with foredom rotary tool till its match with new diameter piston (its kind of dentist drill tool)

PS : not all of gs250 here has do boreup...mostly still using original piston including me...
But replace stock piston with larger diameter still a common mod even for a 125cc cub

[spldart]

Ok. I got a question.
78 mm is definitely WAY out of tolerance for suzuki spec for the cylinder.
What kind of reliability are people doing the 78 mm overbore getting?
... and the 76 mm overbore?

I can believe crazy stuff like that has been done but I'm curious about longevity.

[celesboy1]

Originally Posted by spldart

Ok. I got a question.
78 mm is definitely WAY out of tolerance for suzuki spec for the cylinder.
What kind of reliability are people doing the 78 mm overbore getting?
... and the 76 mm overbore?

I can believe crazy stuff like that has been done but I'm curious about longevity.

pardon me....way out of tolerance ? sure if u use stock boring (3,5mm stock boring...after honing process it will be very thin or....gone)....but in here we ALWAYS buy new diesel engine boring

gz have 3,5mm stock boring


very good question...durability and reliability

- story is....back then several years ago when boreup and strokeup is not popular for commuter bike (at those time people still doubt about durability after the mod)...coz...yes...many of boreup mod blow (broken) and cylinder jugs was rip apart....and u can say if its totally fail...big yes...(perhaps its happened early 2000 , i don't recall it precisely)

but...for certain people (street illegal racer or even legal cub bike race FFA trophy) its not too expensive to repair when their engine blows(just need 1-2days to overhaul + about USD100-150....they dont care as long as they win and get some hundred USD or trophy...(nowadays theres still many cub race whether legal and illegal...both of it still have huge fans)

so...in FFA class....cub that originally for example 125cc....may free to tune till the max include increase displacement as big as they can do....

when it blows....they will start over and over to repair those broke engine....

so...in the end...many of bike tuner (garage) realize...."why dont we do some research to mod engine for non-racer person ?" so they can have faster bike without buy new bigger bike...

still...precision honing machine(plus few other purpose of machinery) and high skills/experienced tuner guy absolutely needed for this kind of mod...

since its just needed few hundred bucks (in USD currency)....theres many people interested with modding engine (moderate specs....not race specs)
coz even its fail...its wont damage their(bike owner) wallet too much...

years by years passed....and in the end....they (mechanic/tuner) has many experienced for mod up commuter engines without being fail (coz they was learned what kind of things that makes their mod fails in past)

so...i will make sure if the mechanic competent before send my bike into garage (not all mechanic have certain skills and experience and high precision honing machine...cnc machine...etc)

but if 3 factors above are met....boreup and strokeup bike will ready even for interstate long haul journey

even few garage offer exclusive research for each person(depend on bike owner budget)....(but its need long time...about a month from start to finish)


PS : there's 2 most reason why boreup engine blow
- compresion ratio is too high (after boreup/strokeup....we need to measuring cylinder compression and make sure its not to high that can make piston tear apart)

- thickness of boring....yes , originally GZ has 3,5mm thickness boring...so we need to stay in those measurement no matter what or better if we can add little more thickness (exsample 4mm) measuring after honing bore process done

[celesboy1]

some exsample if its fail

before and after repair (cost about US$20 for repair fee)

[spldart]

So bottom line is if we US/Canadians wanted to do a crazy overbore then we need a machine
shop that has experience machining, outside the box, on this particular motor.

One thing is for sure. Your typical good, bad or otherwise machine shop here in the US will
not allow us to do this mod because of insurance reasons because it's way to far out of
Suzuki tolerance.
Heck. Barely anyone will turn a rotor even a thousandth past tolerance anymore.

I need to make friends with a new machine shop. This sounds fun and the only way I could
do it here is to have it happen 'off the books'.

[celesboy1]

Originally Posted by spldart

So bottom line is if we US/Canadians wanted to do a crazy overbore then we need a machine
shop that has experience machining, outside the box, on this particular motor.

yes...a big yes...lathe machine , honing machine , pneumatic grinder, even cnc machine perhaps...is what u need

Originally Posted by spldart

One thing is for sure. Your typical good, bad or otherwise machine shop here in the US will
not allow us to do this mod because of insurance reasons because it's way to far out of
Suzuki tolerance.
Heck. Barely anyone will turn a rotor even a thousandth past tolerance anymore.

ohh...i see....
theres no insurance in here at all

Originally Posted by spldart

I need to make friends with a new machine shop. This sounds fun and the only way I could
do it here is to have it happen 'off the books'.

yes...modding bikes is fun things to do....(i dont want my bike totally same with another even its still same GS250)...dont take it wrong....many of tuner here are booksworm too...and perhaps one of their bible was in pics below