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Hi all I’m thinking about fitting a 180cc big bore kit to my yzfr 125 I was just wondering if any of you know what the best bore kit and other extras to get the most amount out of it and to keep it as reliable as I can
 

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2008 YZF-R125 (180cc)
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I've used the WM racing ones so far and have been very happy with them. I had one on my old engine and did 6k miles on it before the bearings gave out (old engines, plenty of compression still). The finish on the plating and maching looked very clean. I'm just running in a freshly rebuilt engine on another WM cylinder with a custom crank setup and loving it so far.

what year bike is it?

caution with a 180 though - I believe the bigger piston changes the engine's running characteristics which (in my case) meant it didn't run well at high rpm, and ofc that's the main thing i was interested in doing with it. I made some changes on the new engine I just finished to try and correct the balance thing and that seems much happier at high rpm, but means taking the crank apart which is not trivial.

I did a video on the balance thing here:

I think 180cc is something which has more knock-ons than people realise, if you want to end up with something usable longer term anyway. e.g. see the clutch upgrade video.
 
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