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90” Monster Bore Kits for Evo XL and Buell!
1991 and up.

3.875” bore kits deliver a whopping 90 inches to your big bore project in your OEM cases! This bore size can only be achieved by utilizing one piece aerospace alloy cylinders and plating process. Don’t be fooled by the imitators. Go fast with the innovators! From a stump pulling touring machine to an all out race bike. This is THE kit to have to be as big as you can be!

Available - natural silver, all black, and black with highlighted fins.

Kits come complete with Revolution cylinders, forged pistons, wrist pins, circlips, and gaskets as well as a lifetime warranty.

XL/Buell Case Boring Instructions
XL/Buell Case Boring Instructions:

Boring your cases to accept your new big bore kit can be quite the challenge for the inexperienced and should only be attempted by trained personnel with the proper equipment. Various suppliers make jigs that vastly simplify the process the do-it-yourself home mechanic. If you must tackle it yourself please invest in one of these. Supplied below are the case bore dimensions for the respective models:

All cases must be bored with a center case through bolt!

Before your cases can be bored you must drill out the existing threaded hole in the right (cam side) case half with a 5/16” drill. Once this is accomplished, machine a flat area centered over the new hole in the outer case surface with a .875 flat end mill to achieve just enough surface for the flat washer to sit on. Put the case halves together and insert a 5/16” x 5” grade 5 socket head cap screw through the center hole and tighten. Be sure that you have flat washers on both ends of the bolt! You are now ready to mount and bore your cases in the manner that you so choose. You will find that the middle section of the bolt will be milled along with the cases as go. This is normal and reinforces the need to be sure that your flat washers are in place as you go.

Available Compression Rratio

10.5 to 1
12.0 to 1

3.875” Big Bore Cylinders (90” Kit) – 4.010” x 1.500”