Cummins 4B 3.9L, 6B 5.9L, ISB, QSB New Valve Spring Locks | Replaces 3940123, J940123

Overview

We stand behind every part we sell — new, rebuilt, or used. While RF Engine is not the manufacturer and cannot extend additional warranties, we do guarantee that each product will arrive as described, in usable condition, and free from material defects or misrepresentation.

Warranty Coverage

• New Parts: Covered under the original manufacturer’s warranty. All terms and coverage are set by the manufacturer. Copies available upon request.
• Rebuilt, Reconditioned, and Used Parts: Backed by an inspection-only warranty unless otherwise stated. As with new parts, RF Engine cannot provide further warranty coverage beyond the manufacturer’s terms.
• No Additional Warranty: RF Engine does not offer any express or implied warranties. However, if an issue arises, we are here to assist and will support you through any applicable manufacturer claim process.

Our Guarantee

All parts are guaranteed to be in the condition stated at the time of sale and free from misrepresentation. If something isn’t right, we’ll work with you to resolve it — including returns, exchanges, or refunds when appropriate.

• We sell parts — we don’t make them — but we stand behind what we sell.
• Guaranteed to match the description or your money back.
• Manufacturer’s warranty applies where available; we’ll help if you ever need it.

Used Parts — What to Expect

Used parts are cleaned, inspected, and guaranteed to be usable, but please note:

• They often have signs of wear, surface rust, blemishes, or cosmetic imperfections.
• They may include old gaskets or residue and likely require further cleaning or machining before installation.
• They are not refurbished, remanufactured, or restored to like-new appearance.

We recommend careful inspection and strongly encourage installation by a qualified heavy-duty diesel mechanic.

• Worn, not worn out — used parts may show signs of age but are fit for service.
• All used parts are tested for usability, not appearance.

Questions?

If you have questions about a part’s condition, warranty, or how we handle returns and guarantees, feel free to contact us. We’re here to help.

Last Updated: June 22, 2025