Genuine Mazda 1.6L Inlet Valve Spring • BJ01-12-125

Genuine Mazda BJ01-12-125 1.6L Inlet Valve Spring

Replacement Genuine Mazda inlet valve spring for Mazda MX-5 Mk1 / NA models fitted with the early 1.6L B6 petrol engine from 1990 to 1993 listed in the compatibility table.

The inlet valve spring is fitted within the cylinder head and keeps the inlet valve closed securely against its valve seat when the camshaft is not opening it. After the camshaft lobe passes, the spring returns the valve to its closed position.

Correct spring tension is essential for reliable valve control, stable compression and accurate valvetrain operation throughout the engine-speed range.

This listing supplies one Genuine Mazda inlet valve spring. The four-cylinder 16-valve B6 engine uses two inlet valves per cylinder, meaning eight inlet valve springs are required when replacing the complete inlet spring set.

Replacement may be required where the original spring is cracked, distorted, corroded, weakened or outside its specified free length or installed-pressure tolerance. Possible symptoms can include valvetrain noise, poor compression, misfiring, reduced performance or valve float at higher engine speeds.

• Part type: Inlet valve spring
• Primary use: Returns the inlet valve to its closed position and maintains valve control
• Location: Cylinder head / inlet side of the valvetrain
• Vehicle application: Mazda MX-5 Mk1 / NA 1.6L
• Confirmed year range: 1990-1993
• Chassis application: NA6C
• Engine application: B6ZE(RS) 1.6L petrol engine
• Quantity per cylinder: Two inlet valve springs
• Quantity per engine: Eight inlet valve springs
• Quantity supplied: One spring
• Brand: Genuine Mazda
• Part No.: BJ01-12-125
• Also referenced as: BJ0112125
• Fitment restriction: Early Mk1 / NA 1.6L application only
• Not allocated to: 1994-1998 1.6L or 1.8L models

Fitment advice: This spring is confirmed for the early 1990-1993 MX-5 Mk1 / NA 1.6L application. Match the original spring type and engine specification before installation, particularly on imported, modified or previously rebuilt cylinder heads.

Other items to consider: When changing this part, you may also want to consider purchasing valve stem oil seals, inlet valves, valve spring retainers, valve collets, valve guides, exhaust valve springs, a cam-cover gasket, cylinder-head gasket and timing-belt components where the cylinder head is being rebuilt.

Useful tools / consumables: Valve spring compressor, vernier caliper or spring-height measuring equipment, spring-pressure tester where available, magnetic pick-up tool, clean component trays, engine assembly lubricant, socket set and calibrated torque wrench.

Difficulty guide: DIY Difficulty: Advanced. Replacement requires cylinder-head and valvetrain dismantling, controlled compression of the spring and correct installation of the valve retainer and collets. Spring condition and installed height should be checked during assembly.

Why Genuine Mazda? Genuine Mazda valve springs are manufactured to the intended free length, spring rate, installed-pressure and material specification. Using the correct OE spring helps retain reliable valve control and compatibility with the original Mazda valve, retainer, collets and cylinder-head components.

What’s in the box: One Genuine Mazda inlet valve spring, part number BJ01-12-125. The valve, retainer, collets, valve stem seal and other cylinder-head components are not included.

Installation notes: Inspect the valve, guide, retainer, collets and spring seating surfaces before assembly. Compare the replacement spring with the original component and measure its free length where appropriate. Install the spring in the correct orientation, compress it using a suitable valve spring compressor and confirm that both collet halves are seated securely before releasing the tool.