Genuine Mazda Cylinder Head Bolt • B660-10-135A

Genuine Mazda Cylinder Head Bolt

Replacement Genuine Mazda cylinder-head retaining bolt for Mazda MX-5 Mk1 NA, Mk2 NB and Mk2.5 NB-FL models fitted with 1.6- or 1.8-litre petrol engines.

The bolt passes through the cylinder head and threads into the engine block. Together with the remaining head bolts, it applies the clamping force required to secure the cylinder head and compress the head gasket evenly against the block.

Correct and consistent cylinder-head clamping is essential for maintaining combustion sealing and keeping the engine-oil and coolant passages separated. A damaged, stretched or incorrectly tightened bolt can compromise the sealing load across the cylinder head.

Ten cylinder-head bolts are fitted per engine, while this listing supplies one Genuine Mazda bolt. Order a quantity of ten when replacing the complete engine set.

Washer information: Each cylinder-head bolt is installed with a separate plain washer. The washer is not included with this listing and should be inspected or renewed separately as required.

• Part type: Cylinder-head retaining bolt
• Common names: Head bolt / cylinder-head fastener
• Mazda catalogue description: Bolt, Cylinder Head
• Installation position: Through the cylinder head into the engine block
• Function: Applies the specified cylinder-head and head-gasket clamping load
• Engine applications: 1.6- and 1.8-litre petrol engines
• Quantity fitted per engine: 10
• Quantity supplied: 1 bolt
• Plain washer included: No
• Cylinder-head gasket included: No
• Other cylinder-head bolts included: No
• Brand: Genuine Mazda
• Part No.: B660-10-135A
• Previous Mazda reference: B660-10-135
• MX-5 fitment: Mk1 NA, Mk2 NB and Mk2.5 NB-FL 1.6 and 1.8 models

Typical reasons for replacement:

• Cylinder head removed for gasket replacement or engine repair
• Original bolt stretched beyond the permitted service limit
• Bolt threads damaged, corroded or cross-threaded
• Drive head rounded or damaged during removal
• Bolt bent or visibly distorted
• Incorrect non-standard fastener previously installed
• Cylinder head or engine block being replaced
• Complete engine rebuild or refurbishment

Quantity advice: Ten bolts are required for a complete MX-5 engine. This listing supplies one bolt per order quantity.

Fitment advice: This bolt is used across the 1.6- and 1.8-litre NA and NB-family MX-5 engine ranges. It should not be confused with the smaller camshaft-cover, bearing-cap or engine-bracket fasteners.

Replacement advice: Cylinder-head bolts must be inspected and handled according to the applicable Mazda workshop procedure. Where the procedure or measured bolt condition requires replacement, renew the affected bolts before reassembly.

Washer advice: Inspect the separate washer beneath each bolt for scoring, distortion, corrosion or an uneven seating face. A damaged washer can affect bolt seating and the applied clamping load.

Thread inspection: Clean and inspect the engine-block threads before installation. A new bolt will not correct damaged, contaminated or previously cross-threaded block threads.

Tightening advice: Install and tighten the cylinder-head bolts only in the sequence and stages specified by Mazda. Incorrect order, lubrication or tightening procedure can distort the cylinder head or cause an uneven head-gasket seal.

Engine-work advice: When the cylinder head has been removed, inspect the head and block sealing surfaces for distortion, corrosion and damage. The cylinder-head gasket must be replaced before reassembly.

Other items to consider: Inspect or replace the cylinder-head bolt washers, head gasket, locating dowels, camshaft-cover gasket, inlet-manifold gasket and exhaust-manifold gasket while the engine is dismantled.

Useful tools / consumables: Correct socket, calibrated torque wrench, angle gauge where required, thread-cleaning equipment, straight edge, feeler gauges and suitable parts cleaner.

Difficulty guide: DIY Difficulty: Advanced. Cylinder-head removal and installation require substantial engine dismantling, accurate inspection and strict adherence to the Mazda tightening sequence.

Why Genuine Mazda? Genuine Mazda cylinder-head bolts match the original thread, length, drive profile and fastener specification. Correct hardware is essential for applying the intended and repeatable clamping load across the cylinder head.

What’s in the box: One Genuine Mazda cylinder-head retaining bolt, part number B660-10-135A.

Installation notes: Clean the bolt, washer seating area and engine-block threads before assembly. Install the correct plain washer beneath each bolt and start every bolt by hand to prevent cross-threading. Tighten the complete bolt set only in the specified sequence and stages using the applicable Mazda workshop procedure. Do not substitute general-purpose fasteners of unknown specification.