Crankshaft Key for QMB139 Engines
Woodruff Key for 50cc 4-stroke QMB139 engines.
- Length: 12.9mm
- Width: 3mm
- Height: 2.5mm
As Seen On
GoKartsUSA is one of the largest online dealers for top industry brands including TrailMaster, IceBear, and RPS.
We offer lifetime technical support—free, knowledgeable, and based right here in the USA.
Every purchase includes manufacturer-backed warranty coverage, including up to one year of engine warranty protection.
We feature authentic customer product reviews so you can shop confidently with real feedback from real riders.
Our checkout process is secure, simple, and designed to make buying your next ride fast and stress-free.
We maintain guaranteed parts support for active TrailMaster, IceBear, and RPS models—so you can keep your ride running strong for years.
Frequently Asked Questions
Orders containing in-stock items typically ship within 3–5 business days. Orders that include assembly will require 7–10 business days to prepare. Please note that during the holiday season (Thanksgiving through Christmas), processing times may be longer due to high order volume.
Once your order has shipped, you’ll receive an email with tracking information. Most orders are shipped via Less Than Truckload (LTL) freight and generally arrive within 3–7 business days. Deliveries to remote areas (such as mountains, forests, valleys, or islands) may take longer. You can check the estimated delivery date on the carrier’s website using the tracking number we provide.
Unless otherwise noted, the vehicles we offer are shipped crated or on a pallet and do not come assembled unless you’ve selected our assembly service. Assembly typically requires a few basic tools and mechanical knowledge. If you're not confident in your ability to safely assemble a high-speed off-road vehicle, we strongly recommend selecting professional assembly or having it assembled by a local mechanic.
Yes. Buy-now-pay-later financing is available with our preferred partner, BreadPay® (please see their icon under product pricing for details).
Please call 888-886-5846 and talk to one of our knowledgeable sales representatives between 9am–3pm PST. Or email us at orders@gokartsusa.biz.
You're covered with confidence at GoKarts USA®. Your satisfaction is our top priority. Every purchase comes with manufacturer-backed warranty protection—including up to 12 months of engine coverage—to keep your ride running strong. TrailMaster products also include a 6-month parts warranty for added peace of mind.
For shipping safety, most vehicles cannot be fully assembled prior to delivery.
Minor assembly is required—this typically includes installing mirrors, connecting the battery, adjusting handlebars, and other small components. Before operation, please ensure all screws and fasteners are tightened, engine fluids are at proper levels, and the battery is fully charged. Your factory warranty remains valid right out of the box.