1994 – 2001 Yamaha YZ125 Piston – Installation

How to Install your 1994 through 2001 Yamaha YZ125 Piston

The Tools You Will Need

• Safety Glasses → https://bulltru.com
• Dremel with Sanding Disc → https://amzn.to/407t6l3
• 2-Stroke Oil → https://amzn.to/3WnyXSl
• Assembly Lube → https://amzn.to/4ar8mty
• Calipers → https://amzn.to/3BRoCXX
• Brake Cleaner → https://amzn.to/4jv9v7a
• Socket Extension
• Feeler Gauge → https://amzn.to/4nrpkwx

The Parts You Will Need

• New Piston Kit → https://amzn.to/3KXHY1w (Check Your Size)
• Piston Ring → https://amzn.to/47cDyLx
• Wrist Pin Clips → 93450-16068-00
• Top End Gasket Set → https://amzn.to/4hlHG0D

Pre-Service Notes

• I recommend opening the Service & Torque Specs in a new tab for easy reference.
• If you need parts and tools, make sure to buy them here! → https://amzn.to/4h4lDKq
• Pictures with captions are below after step.
• If you need any help don’t hesitate to ask!

Yamaha YZ125 Piston Installation

• Start by covering your crankcase opening with a shop towel.
• If you drop your clip, you will spend an absurd amount of time trying to fish it out of the crankcase before you realize it would have been faster to just split the case again. But that wasn’t me…
• I am using Lucas assembly lube, but 2-stroke oil will work just fine, but you will need to use a lot of it.
• Apply assembly lube to the needle bearing, and install it into the connecting rod bore.
• Old or new, your piston should have an arrow or the word “IN” stamped on the crown.
  • If it’s an arrow, point it toward the FRONT of your bike.
  • If it has “IN”, that side goes to the rear.
• Position your piston accordingly, and apply assembly lube to the wrist pin.
• Push your wrist pin all the way to the opposite side pin clip.
• While wearing your safety glasses… Install the second pin clip with the opening facing up.
  • On the second clip, I nicked the piston with the clip end, but I was able to smooth it out with emery paper.
• Keep the towel in place until you install the cylinder.

If you have any questions, please let me in the comments, or send me a DM!

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