Genuine Mazda Uprated Inlet / Exhaust Valve Spring • LF9G-12-125A

Genuine Mazda LF9G-12-125A Uprated Inlet / Exhaust Valve Spring

Genuine Mazda uprated valve spring for Mazda MX-5 Mk3, Mk3.5 and Mk3.75 NC models with compatible 1.8 L8-VE or 2.0 LF-VE MZR petrol engines.

This is the later, slightly stiffer valve spring introduced with the facelift MX-5 NC2 engine specification. Mazda fitted this spring to later 2.0-litre manual-transmission models, while it is also commonly used as an uprated replacement in compatible earlier NC 1.8 and 2.0 engines.

The spring fits around the valve stem between the cylinder head and spring retainer. It closes the valve after the camshaft lobe has opened it and maintains contact between the camshaft, tappet and valve throughout the engine-speed range.

MazSpec identifies the later spring as the uprated NC2-onward design introduced alongside the increase in the 2.0-litre engine speed limit from approximately 7,000rpm to 7,500rpm.

The same spring is used on both inlet and exhaust valves. Sixteen springs are fitted to each sixteen-valve engine, and this listing supplies one Genuine Mazda spring. Select a quantity of sixteen when replacing the complete engine set.

Fitment distinction: Direct Mazda catalogue fitment is documented for 2009–2015 MX-5 2.0-litre manual-transmission models. Installation in earlier NC1, 1.8-litre or automatic-transmission engines should be treated as an uprated engine-build application rather than a simple catalogue-identical replacement.

• Part type: Engine valve spring
• Application: Inlet or exhaust valve
• Spring specification: Later uprated NC2 / NC3 design
• Location: Cylinder head valvetrain
• Function: Returns the valve to its seat and maintains valvetrain control
• Quantity per valve: 1
• Quantity fitted per engine: 16
• Quantity supplied: 1 valve spring
• Inlet and exhaust application: Same component
• Valve included: No
• Spring retainer included: No
• Valve collets included: No
• Valve-stem seal included: No
• Tappet included: No
• Brand: Genuine Mazda
• Part No.: LF9G-12-125A
• Earlier Mazda reference: LF9G-12-125

Typical reasons for replacement or upgrade:

• Broken or visibly damaged valve spring
• Reduced spring pressure caused by fatigue
• Valve float at elevated engine speed
• Uneven installed spring heights
• Cylinder-head rebuild
• Valve or camshaft replacement
• Performance or higher-revving engine build
• Upgrade from the earlier NC1 spring specification

Fitment advice: For a standard direct replacement, this spring is documented for later MX-5 NC2 and NC3 2.0 manual-transmission engines. Its use across earlier 1.8 and 2.0 NC engines is based on the compatible MZR cylinder-head architecture and should form part of a properly specified valvetrain build.

Replacement advice: Valve springs should be measured and compared for free length, installed height and spring pressure. Where one spring has failed through fatigue or over-revving, inspect and measure the complete set rather than replacing the visibly damaged spring alone.

Other items to consider: Inspect the valves, valve guides, spring retainers, collets, valve-stem seals, tappets, camshafts and timing components. Confirm piston-to-valve clearance and valvetrain compatibility where aftermarket camshafts, valves or cylinder-head machining are involved.

Useful tools / consumables: Suitable valve-spring compressor, compressed-air cylinder adapter or cylinder-head support fixture, magnetic collet tool, micrometer or vernier caliper, valve-spring tester, calibrated torque wrench and clean engine assembly lubricant.

Difficulty guide: DIY Difficulty: Specialist / Advanced. Replacement requires controlled compression of the valve spring and secure retention of the valve. Incorrect collet installation or spring selection can cause severe internal engine damage.

Why Genuine Mazda? Genuine Mazda valve springs are manufactured to match the original spring diameter, installed height, seat profile and valvetrain geometry. The later uprated specification provides the intended spring control for the revised NC2 and NC3 engine-speed range.

What’s in the box: One Genuine Mazda uprated inlet or exhaust valve spring, part number LF9G-12-125A.

Installation notes: Follow the applicable Mazda workshop procedure and prevent the valve from dropping into the cylinder before compressing the spring. Remove the collets, retainer and original spring carefully, keeping reusable components identified by position. Inspect the valve, guide, spring seat and retainer before installation. Measure the replacement spring and confirm the required installed height. Fit the spring in the correct orientation where specified, install the retainer and ensure both collets are fully and evenly seated. After completing the work, rotate the engine manually and confirm correct valvetrain operation before starting it.