Zipper’s Milwaukee-Eight® Big Bore Cylinder Kits
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Increasing the size of a Milwaukee-Eight® engine is easy with Zipper’s Big Bore Cylinder Kits.
The Milwaukee-Eight® engines design is made for displacement increases and Zippers offers cylinder kits for Factory stock 4-valve head, SE heads and many Custom High Flow Heads to provide huge torque and horsepower gains.
Each of this specific bore sizes are designed to fit on the factory engine base without case boring just like like-stock installation.
4.250- 4.280 Bores
Zipper’s offers new alloy castings with bore sizes from 4.250 to 4.280
These castings are designed with additional aluminum for added strength vs a O.E. casting with a larger bore liner with the following features:
• Cast Aluminum has 1 lb. additional material for Strength and Reliability
• Stress Relieved Iron Liners
• Precision Sized on Sunnen SV-30 by Zipper’s skilled craftsman
• Special Ring Packs for Advanced Cylinder Sealing
• Gasket Surface Finish Improved for Superior Seal using Cometic MLS Gaskets
• Zipper’s Forged “Spec Built” Pistons manufactured by CP
We have many dome configurations to choose from so you can target various compression ratios. Contact Zipper’s support if you have a special requirement.
4.250 x 4.375 stroke = 124ci
4.250 x 4.500 stroke = 128ci
Kits include precision fitted cylinders with tight tolerances, 2618 forged pistons with advanced ring packs, pins & clips, head and base gaskets and new head bolts. The rings custom sized to each cylinder.
Not legal for sale or use in California on any pollution controlled motor vehicle.
Not legal for sale or use on any EPA pollution controlled motor vehicle.
***To ensure you enjoy a premium experience with a Zipper’s Cylinder Kit, Please fill out a Job Order Sheet prior to completing an order on the website.
Click here for Zipper’s Job Order Sheet
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Mike –
Put the 128 sleeper kit in a 2019 heritage softail at the shop customer was super happy made great power and torque. Another great product from zippers keep up the good work guys. And as always great customer service.
Joe Ritchey –
AMAZING results with the #517-986 Sport-Tour 128 Kit on my 2021 Roadglide 117. . . . I considered the 128 Muscle kit but chose the Sport Touring with 6 less HP but 4 more ft.lbs. torque. This engine is as tame as a factory stock engine when riding gently, but an absolute beast when I open it up. The torque comes on strong at low RPM and never lets up, and the fuel economy is over 40 MPG when I ride it sensibly. I’ve owned dozens of custom engine builds in 50+ years and never had such a perfect balance between rideability and performance. Anyone can build an engine that shows big numbers on a dyno sheet but is worthless in the RPM ranges we use every day. There’s no question these Zippers kits are the best in the industry.
Matt Matthews –
Was disappointed with breakout 117. Don’t know what Harley did but far less peppy than my 117 on my road glide. I recently had 128 big bore plus 468 cam. Still building up miles for a final tune. I can tell you this is the motor that should have come with the breakout. I am keeping bike under 3500 for first 500-600 miles and then aggressive tune. It is peppy down low and after second gets up and goes all the way through 6 gear. I wanted more low end torque and man do you get it with the 468. This was truly money spent!