“Sleep-er” (slang) A vehicle which has been internally modified while retaining a mostly stock appearance in order to fool opponents in a drag race, or to avoid the attention of the police.

This powerful kit by Zipper’s transforms your 114″ or 117″ M8-powered machine to 4.250″ bore 128″ with a drop-on piston & cylinder kit. The Sleeper 128” kit is based around new-production cylinders and pistons, designed specifically by Zipper’s for durability and improved oil control. The new cylinders are then treated to the best precision boring and honing process you can find, as our technicians precisely measure each piston to provide skilled, old-fashioned sizing processes to the cylinders. Mounted in special torque plates, a CNC-hone is used to create a straight and true finish, topped off with brush-finish technology that requires minimal run time for ring seating while providing best power. The Red Shift 472 cam (for a Sophisticated Balanced Power setup)  is packaged up with a new full complement cam bearing, top end-cam chest gasket set along with a set of Quickee pushrods and covers to simplify reassembly.

This is a hugely cost-effective way to increase the power of the Milwaukee-Eight® engine – with stock heads and a stock throttle body! While your engine is apart, we HIGHLY recommend that you do a full inspection of the cylinder heads for seat or guide issues, and we do provide new valve seals in the gasket kit for reassembly. If you are not equipped to perform the inspection or repairs to your stock heads, Zipper’s offers these services and more, just give us a call!

This kit represents the basic parts required to turn your 114” or 117″ into a big-torque 128”. As expected, you will need a properly designed Exhaust System, a robust Tuner System to recalibrate fuel and spark curves/or we suggest ThunderMax to replace your factory-equipped ECM, properly sized higher-flowing injectors, a high-flow Air Cleaner and a stronger clutch-pack and slave cylinder to be able to handle the torque. Please call Zipper’s for advise on dressing out your Sleeper 128” kit. We can assist regardless if you do or don’t already have a Tuner / Air Cleaner / Exhaust system on your motorcycle. Also, if you already have a Red Shift 472 installed in your engine, please call for an updated kit price that doesn’t include the parts you may already have.


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, Please fill out a Build Sheet/Job Order Sheet prior to completing an order on the website.
Click here for Zipper’s Build Sheet/Job Order Sheet

Weight 25 lbs


Engine Type

Fuel / Air

Emissions Compliant

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