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North UK

Hey.  The 125 crank cant support 250cc pistons because extra volume the cylinder makes and extra hp will snap the crank and conrods.


The 125cc cam chains are too slim to spin 250cc camshafts (they use chains that are 2-3x wider and stronger)  the 250cc cylinder head also has much stronger springs causing more strain on the crankshaft.

You can however fit some better HD clutch plates and upgrade to 520 chain kit to customize gearing.


Any mods on your 125 cylinders should be *slightly* custom stronger 10% extra valve springs , port polishing , maximum 64-66 piston big bores (custom, i have no info on this as not one really does this) , head skimming.   Thats about it for the valves and cylinder heads that way the 125cc crank wont snap away.

// Meditation doesn't mean you have to sit still....