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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.

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