This video is me trying to reassemble the broken motor for my YZF-R125, this time with a 180cc big bore kit. Link for the cylinder I bought (which looked *beautifully* machined): https://www.ebay.co.uk/itm/151763913131

Apart from that I only ended up buying the top cam chain guide and one replacement head bolt (which looked like it was going to round off) and a bunch of oil and filters. I’d bought a new cam chain too but hadn’t realised you have to split the bottom end casing to fit it..and you’re supposed to change the main shaft, cam chain and cam gear as a set, so i guess not this time.

Videos I found helpful for preparing the piston, rings and wrist pin etc:

wrist pin fitment (this was super useful):
https://www.youtube.com/watch?v=siG5W…

measuring ring gap:
https://www.youtube.com/watch?v=zHK1M…

installing rings:
https://www.youtube.com/watch?v=rgu5v…

My links:
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