Increasing the size of a Milwaukee-Eight® engine is easy with Zipper’s Big Bore Cylinder Kits.

Milwaukee-Eight® engines respond to displacement increases like no other HD engine! Factory stock, the 4-valve head flows a lot of air so making the engine bigger rewards the rider with huge torque and horsepower gains. Our kits include new cylinders that drop right on the factory case for like-stock installation.

4.125 and 4.250 Bores

Zipper’s offers new big bore castings with bore sizes from 4.125 to 4.250.

These castings are more durable than the O.E. units with the following features


  • New Design Cast Aluminum Alloy for Strength and Reliability
  • Stress Relieved Iron Liners
  • Precision Sized by Zipper’s with the most Advanced Processes
  • 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 dome configurations for all bore sizes that will drop on any H-D 107, 114 or 117 H-D engine. The dome volumes are for OE or SE M8 heads or larger valve heads with increase chamber size with compression up to approx. 11:1

4.125 X 4.375 stroke = 117ci

4.125 x 4.500 stroke = 120ci

4.250 x 4.375 stroke = 124ci

4.250 x 4.500 stroke = 128ci

Kits include fitted cylinders, pistons with rings, pins & clips, head and base gaskets and new head bolts. The rings custom sized to each cylinder.

***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

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.

Weight 1 lbs

Country of Origin

Engine Type


Customer reviews

Rated 5 out of 5 stars
1 review
4 stars 0 0 %
3 stars 0 0 %
2 stars 0 0 %
1 star 0 0 %

1 reviews with rating of 5 stars (1 of 1)

(Show unfiltered results)

1 review for Zipper’s Milwaukee-Eight® Big Bore Cylinder Kits

Add a review

Use one of the allowed file type: jpg,png.

    You may also like...