Dan originally contacted Re-Do Banshee about a transmission fluid leak on his Yamaha Banshee engine. The leak appeared to be coming from around the drain plug area, possibly caused by spider cracks in the stock cases.

At first, the goal was simple: reseal and repair the engine.

But once Dan began disassembly, the project escalated. The input shaft bushing would not come off, and the primary gear was stuck on the crankshaft. Rather than continue fighting aging stock cases — especially ones that may have continued leaking — Dan decided to send the partially disassembled engine to our shop.

After discussing options, he chose to upgrade instead of repair.

We ordered new Driveline Performance engine cases along with Assassin cylinders and moved forward with a full 421 cc build.

While waiting for the new parts to arrive, Virgil carefully disassembled and inspected the original engine. The stuck bushing and primary gear were safely removed without damage (you’ll see that in the video below).

Once the new cases and cylinders arrived, the engine came together smoothly. The usable internals were transferred into the new cases, the 421 top end was assembled, and the engine passed leak down testing. After final assembly and a successful test stand run, the engine was shipped back to Dan.

What started as a leaking drain plug repair turned into a fully refreshed 421 cc Assassin Yamaha Banshee engine built on brand-new cases — completed in about two weeks from first contact.

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

Project Specs

• BUILD NAME:  Dan's 421 Assassin Build
• EXPECTED RIDING CONDITIONS:  About 700 ft elevation. Mostly dirt trail riding. 
• DISPLACEMENT:  421 cc
• CYLINDERS:  Assassin Nikasil
• PORTED:  As cast - no additional porting
• PISTONS: Wiseco Blaster Pistons 68 mm 12198M06800
• CYLINDER HEAD:  Redline Racing Head with RE-DO logo
• DOMES:  23 cc
• CRANKSHAFT:  58 mm (4 mm over stock)
• COMPRESSION:  155 psi
• REEDS / CAGE:  Mototassinari VForce4
• CARBS:  Smart Carbs - we heat cycled this engine with Keihin PWK 35 mm carbs in our shop. Dan installed the engine into his Banshee with the Smart Carbs he had.
• CARB JETTING:  Smart Carbs do not use jetting
• NEEDLES:  Smart Carbs do not use jetting. They use metering rods. 
• AIR SCREW ADJUSTMENT:  
• FUEL RECOMMENDATION:  Premium Non-Ethanol (pump gas)
• WATER PUMP IMPELLER:  Stock
• CLUTCH:  Stock clutch with 3 stock springs and 3 heavy duty springs
• EXHAUST:  Shearer small bore pipes 
• TIMING:  Set to 6 degrees advanced