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Rebore 100cc out to 125+

Guest Backontwowheels

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Hello all,

I am new to the forum but not new to motorbikes, I had quite a few years ago, now with the price of fuel, looks like I'll be back on two wheels again, I am looking forward to it,

I have just got hold of a 1990 Suzuki GP100, with some spares, the person who sold me it was going to Have it bored out to 125+

Can anybody advise! is it possible to turn a GP100 into a 125, if it is, what would I need.

Any advice would be most appreciated


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Guest philgale

moved to pitstop,

welcome to the forum mate, jump in newbies and say hello will more likely get more replies if you say hello first...

personally i havnt got a clue.....plenty of people here will know

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From what i've read it's a pretty complicated business, and not normally something you can do in your garage with a blow lamp and a hammer.

You need to bore out the cylinder so it's bigger, but then you'll loose compression because it's so fat, so you have to skim the bottom of the cylinder head to bring it closer to the piston. Both tasks require some serious milling machinery.

Then obviously you'd have to fit an oversized piston.

With regards cooling, I guess if it's water cooled you might have to adjust something to stop it over heating??

Not entirely sure, but it's not an easy job.

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Yup, the cost and reliability issues would be not worth the hassle, also insurance would be a mare as you could potentially be increasing power by 25% and thats a serious mod to a bikes power output!

If you want more go, get a 125 but to be honest, a 100cc bike will be just as fast as a restricted 125 of its era and will be more fuel efficient and its engine will drive better as its not gonna be restricted!

I had a Honda CB100-N and it was awesome fun, my mates used to laugh at me for only having 100cc compared to their 125cc's until I kept up with all of them and out rode them on the twisties coz their big wheel DT's etc would wobble round the bends while the lil 100cc bike took it all in its stride (I also think it kept up with them better on the brakes too as my front brake didn't work so my corner speed was higher along with my blood preassure and heart rate and fear factor! LOL) ;)

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Thanks for the replies! I have now managed to locate a GP125 engine said to of been reconditioned, and only half ran in, I have only got the sellers word for it, but he sent me some images and it do look nice and clean, GP125 engines are like rocking horse poo! should get it sometime early next week, I have searched everywhere and asked everyone, I have spoken to and that's a lot of the biking fraternity, they do say the 125 engine is a good engine for tuning but it's got to be an early one for some reason, I don't know the reason why, but mine should be OK it's a 1983 model/engine so they could be put together better I suppose.

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