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Jeff's 421 Cub Build - Completed Nov 2025

Jeff's 421 Cub Build - Completed Nov 2025

Jeff picked up a Banshee to enjoy at the Oregon coast — but on his very first ride, the crankshaft failed. Since he knew he wanted a solid and exciting engine setup anyway, he reached out to Re-Do Banshee to explore his options. After talking with Virgil, Jeff decided on a 421 Cub build.

The engine turned out great, and Jeff couldn’t be happier with the results. 👍🙂

Watch the Build

Want to watch how this project came together?

  • 👀 Watch the video below. 
  • ⬇️Scroll down for the link to watch the build's whole playlist on Youtube. 
  • ⬇️Continue below to see the project specs below the video.

 

Q- QUESTIONS About Your Project?
A- You can call 📞📱 or message us at 541-419-6054. 

Whether you're restoring a vintage ATV, upgrading your suspension, or planning an engine build, we're happy to help. We specialize in Yamaha Banshees. If you have a different project in mind, contact us and we will let you know if we can take it on and what you can expect. 

We are flexible and will work with you. We offer a range of services. We can:

  1. Help you select the parts for your DIY build and ship them to you.
  2. Help you Pack and Ship your Engine to us, then build your engine and ship it back to you to install.
  3. Complete the whole engine build for you and install in your Banshee.
  4. We can inspect, repair and service the whole Banshee for you if you'd like.
  5. We can build or restore your Banshee, if that's what you need.
  6. We may also be able to locate a local Banshee for you and install your newly built engine in it.

Project Specs

  • BUILD NAME:  Jeff's 421 cc (Cheetah) Cub Build
  • EXPECTED RIDING CONDITIONS:  
  • DISPLACEMENT:  421 cc
  • CYLINDERS:  68 mm Cheetah Cub Cylinders - from Cast Precision Industries, or CPI. 
  • PORTED:  As Cast. This means they are untouched from the casting at CPI. 
  • PISTONS:  Wiseco 68mm
  • CYLINDER HEAD:  Redline Racing Cool Head
  • DOMES:  19 cc
  • CRANKSHAFT:  HotRods 58 mm stroke. This is +4 mil over the stock stroke of 54 mm. Crankshaft was trued and welded.
  • COMPRESSION:  185 / 187 psi
  • REEDS / CAGE:  Mototassinari V-Force 4 Reeds and Cage
  • CARBS:  Keihin 35 mm PWK
  • CARB JETTING:  Started with 170 main jets and 50 pilot jets at our shop. Jeff's Banshee ended up needing larger mains after the plug chop. This 421 is jetted to run at the Oregon Coast.
  • NEEDLES:  CEL
  • AIR SCREW ADJUSTMENT:  2 turns out
  • FUEL RECOMMENDATION:  Race Gas (110-116 Octane)
  • WATER PUMP IMPELLER:  Billet Aluminum
  • CLUTCH:  Modquad Lockout Clutch with Cover
  • EXHAUST:  Shearer Big Bore In-Frame pipes with Shearer silencers.
  • TIMING:  Set to 4 degrees advanced

 

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References:

  • We calculate engine displacement based on the bore in the engine's cylinders and the stroke length of the crankshaft. Click here for more explanation in our Banshee Engine Displacement blog article. 
  • Click here for information about Banshee engine break-in procedures. This includes our recommendations for Fuel to Oil Ratios and Selecting the Correct Fuel.

About the Authors:

This project article was written by Janel with plenty of help from Virgil. Virgil is the Banshee mechanic, and I am the website mechanic. I do own and ride a Banshee, which helps. 

The Re-Do crew hopes sharing our project info and specs may help some with their own projects, or that you find it interesting. I want our technical info to be accurate and helpful.

Please do let us know if you like our project articles, or if you think I need to correct something. You can send an email to info@redo-parts.com - and your comments will be passed along to me. 

Thanks ~Janel 😉👌

Email to: info@redo-parts.com