Engine rebore?

Luke93 · Two Stroke Sniffer Joined: 29 Nov 2011 Karma :

when having your cylinder rebored and piston sized up, what is the cc if it were to be rebored 2.00 oversize, my bike is a 125 suzuki gp. i dont really have a clue about engine rebores to be frankly honest. Also ive heard it makes the bike less reliable, is this true? would be so handy to have the info Smile

cheers
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I love the smell of double u d 4 t in the morning..
motorized bicycles: mz etz125, suzuki gp125

Martay · World Chat Champion Joined: 20 May 2009 Karma :

Based on a 80's gp with a standard 56 x 50 bore a 2mm overbore will give 132cc. Riding it you wont notice the increase in size Wink

BTW, why are you increasing the bore by 2mm for, i presume, the first time. Normally you can start off at .25??
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Luke93 · Two Stroke Sniffer Joined: 29 Nov 2011 Karma :

Yeah you can i think, but why not go for the full hog. just want a bit more leg to her, higher cruising speed really, new sprockets? as she is now pretty custom! cosmetics anyway! shed an grinder has worked magic. consider the fact she looks different even from this picture now, shes an ongoing project, but this is her looking her best..

https://www.flickr.com/photos/71047480@N04/6427474349/in/photostream
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I love the smell of double u d 4 t in the morning..
motorized bicycles: mz etz125, suzuki gp125

Luke93 · Two Stroke Sniffer Joined: 29 Nov 2011 Karma :

yeah but at first i hadn't a clue what 2.00 would do, i dont know too much about rebores and the measurements, but cheers for the info man
____________________
I love the smell of double u d 4 t in the morning..
motorized bicycles: mz etz125, suzuki gp125

MrClifford · L Plate Warrior Joined: 04 Jun 2011 Karma :

Way you work out cc is Pi x stroke x half bore x half bore so
3.14 x 50 x 28 x 28 = 123

If you do rebore do 57 or 57.5 so you still got room to rebore again to 58 as you may need to in the future.. im currently in a dilema as my gp is well iver 58mm and i got no compression and cant rebore aa there are no pistons for it!

You will notice a difference if you rejet it and get a micron exhaust for it but finding a micron is a ball ache!

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

You don't want to go 2mm. It means you've got nowhere to go if you need to re-bore again in the future.

It also changes the compression ratio of the cylinder which means you might actually lose performance.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

Pete. · Super Spammer Joined: 22 Aug 2006 Karma :

That depends on the deck height.

If you re-bore for the first over-size you'll notice the difference because you've basically re-freshed your engine. You'll gain a little more from going to last oversize but not much and as said above - if you have a problem you're out of choices apart from buy a new barrel.
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