129" Big Bore Cylinder Kits / '17-'23 107" M8 Motors
Tax excluded. Shipping calculated at checkout
Ships within 24 hrs. Arrives within 1 - 5 days depending on location
The S&S 129" Big Bore Kit takes a '17-'23 M8 107" motor to 129 cubic inches without altering the crankcase or changing stock engine height.
No Shipping to California.
129 cubic inches out of a 107 is a 20 percent displacement increase, and S&S got there without asking you to split the cases. Bore goes to 4.320" and stroke to 4.375", the crankcase stays as it is, your original engine serial numbers stay with the bike, and the motor sits at the same height it did before. For an M8 owner who wants real displacement without a title full of questions, that combination is the point.
What Comes in the 129" Big Bore Kit
Forged 11:1 pistons carry the compression. All required multi-layered steel head gaskets and hardware ship in the box, so the kit is complete as delivered. A cam cover badge is included as well. Made in the USA.
129" Big Bore Kit Specifications
- Fits '17-'23 M8 107" motors
- 129 cubic inch final displacement
- Bore 4.320", stroke 4.375"
- Forged 11:1 pistons
- No crankcase alteration required
- Retains original engine serial numbers and stock engine height
- MLS head gaskets and hardware included
- Cam cover badge included
- Finishes: highlighted cylinder fins, or without
- Made in the USA
Before You Order the 129" Kit
⚠️ VERIFY that your motor is a 107" M8 in the '17-'23 range, since this kit is specific to that displacement. A displacement change of this size will require retuning and may affect emissions compliance in your state.
Choose options
