YZ426F Piston with 18mm wrist pin

3 replies to this topic
  • decawley

Posted October 25, 2010 - 09:55 PM


Hi, My son and I went to replace the cylinder/piston on a friends 2001 YZ426F. We ordered the piston and cylinder but when we tried to replace the piston we found out that the small end of the connecting rod (where the piston wrist pin fits) was 18mm. The wrist pin that came with the Yamaha top end kit we had purchased was(19mm). According to all the parts fiches I researched this (19mm) is correct. I verified the VIN number from the frame and the bike is a 2001. The Cylinder we removed was a 426. The piston removed from the bike is a 95mm(426) from PROX but the wrist pin is a 18mm pin.
I know that the YZ400 (1998-1999) used a 18mm wrist pin.
Does anyone know where I can find the 426 piston with a 18mm pin or will we need to replace the connecting rod?
Thanks for any help, Damian

  • fmxis4me

Posted October 26, 2010 - 05:52 PM


frame said 1999/11 yz 400 but its really a 2000 yz 426 ordered complete top end cyl everything went to install and the yz 400 has a 17mm wrist pin the 426 is 18.5mm had to take all parts back and get 426 pistion cyl, it might need a con rod if its 19mm

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  • umu24013

Posted October 27, 2010 - 07:19 AM


AFAIK, Wiseco/ThumperRacing were producing 426 pistons (92+3mm bore) for the yz400f several years ago. part# 4649M09500

Not sure if they still sell them.

  • decawley

Posted October 29, 2010 - 02:24 AM


Hey thank you for the info. I found the piston at wiseco.ch. I had e-mailed Wiseco Europe several times and they were trying to tell me the Part # did not exist. The Swiss company had a catalog from 2008 online and they still showed the piston and have 1 in stock. I guess Wiseco does not make the piston anymore.
Have great day and
Thanks again, Damian

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