new cylinder time

3 replies to this topic
  • wr-426

Posted August 20, 2011 - 10:26 PM


Hi guys,

my 426 went bang last night so i stripped it down and took it apart this morning to find a smashed up piston and a cracked cylinder. the cause of the problem was one side of the selector fork in the gearbox breaking off and making it's way up to the crankshaft. now i need a new piston and cylinder.

Who makes cylinders for these bikes (big bore or standard)? what's the bore and stroke? and are the YZ cylinder and pistons the same?

any help would be appreciated, i want to get this bike back in the dirt as soon as possible.


  • Birdy426

Posted August 21, 2011 - 10:05 AM


YZ is the same. Luke's Racing, RPM, and Eric Gorr make big bore kits, as well, I'm sure as others. I'm not aware of any aftermarket manufacturers for the 426's. Best bet is either to try new from Yamaha, or a servicable (or at least reworkable) unit on e-Bay. What I found when doing my cylinder was that a big bore kit from either Luke's or Gorr was a bit cheaper than sending my cylinder out to US Chrome for rework/replate, buying a piston kit from either Wiseco or JE, and a gasket set from Cometic or OEM. Might not be the case for you as you don't have a reworkable cylinder to send back as a core (so you would incur a $200.00 core charge). Good luck!

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  • wr-426

Posted August 22, 2011 - 10:17 PM


thanks Birdy,

I managed to find a good second hand barrel and the gearbox parts here in australia, (lucky me). can't wait to have the bike back in the dirt

  • wr-426

Posted August 23, 2011 - 06:44 AM



I have another question. i sourced all the bits that i should need to put the bike back together except a new crankshaft. i am fairly sure the crankshaft is fine, it has seen a few knocks from the bits of gear floating around but i doubt it has been knocked out of balance. i ran my vernier callipers around the outside of the two counterweights and got measurements within 0.1 mm at all points on the counterweights.

are these acceptable measurements?
is there anything else i should check/measure to see how my crankshaft is?
are these cranks known to be fragile at all or can they take a bit of a beating?

thanks everyone for your help


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