HZ GX390/GX340 Fully Assembled Cylinder Head Kit — Fits Honda GX390 GX340, Complete Gaskets & Valves

Fully assembled replacement cylinder head kit for Honda GX340/GX390 engines, ready to install with valves, gaskets, bolts and feeler gauges included.

This HZ GX390 cylinder head kit delivers a complete, drop-in head assembly compatible with Honda GX340 and GX390 engines and many common clones. It includes the cylinder head, valve cover, valves, valve springs, spark plug, insulation, full gasket sets, muffler gasket, all necessary bolts and nuts, and two feeler gauges for accurate valve clearance setup. The kit replaces Honda part numbers such as 12200-ZF6-406 and 12210-Z5T-416 and matches capacities from 337cc up to 459cc across OEM and clone applications.

What parts come in this fully assembled cylinder head kit?

The HZ kit is intended to be a one-stop replacement for cylinder head rebuilds: you receive the head fully assembled so minimal prep is required before installation. All routine wear items that typically need replacing during a head service are included for convenience.

• Cylinder head and valve cover pre-assembled
• Intake and exhaust valves, valve springs, rockers and pushrods
• Spark plug, spark plug insulator and muffler studs
• Head gasket, valve cover gasket, carburetor gasket set, muffler gasket
• Complete set of bolts, nuts and washers
• Two feeler gauges for intake and exhaust clearance setting

Which engines and equipment will this head fit?

Designed for Honda GX340 and GX390 engines, the HZ head also fits many aftermarket clone engines with similar bore/stroke and mounting patterns. It is commonly used in pressure washers, water pumps, generators and compressors that use 11–16 horsepower small engines.

• Honda GX340, GX390 and GX390T/GX340T variants
• Clone engines: 337cc, 338cc, 340cc, 389cc, 390cc, 420cc, 439cc, 458cc, 459cc
• Applications: 4200–4400 psi pressure washers, water pumps, portable generators and air compressors
• Replacement for Honda OEM numbers listed in product details

How does this assembled head save time and simplify installation?

Receiving the head pre-assembled means fewer individual parts to organize and less bench labor before engine reassembly. Factory-installed items like the spark plug and muffler studs reduce fitment steps; the included feeler gauges let you set valve lash precisely at install time.

• Pre-assembled valve train and fitted studs cut bench time
• Complete gasket sets eliminate missing-seal delays
• Feeler gauges ensure correct valve clearance on first run
• All mounting hardware provided to avoid extra trips for fasteners

What should I check before buying to ensure fitment?

Measure bolt-spacing, port orientation and overall head dimensions against your existing head to confirm compatibility. Cross-reference the OEM part numbers and engine displacement range in the listing with your engine model to avoid fitment issues.

• Compare mounting hole pattern and stud locations to your head
• Verify engine model (GX340/GX390) and displacement against listing
• Check compatibility with your equipment model (pump, generator, etc.)
• Confirm required valve arrangement and spark plug position

Who is this for: This HZ assembled GX390 cylinder head kit is aimed at mechanics, fleet service technicians and DIY enthusiasts who need a complete, reliable replacement for worn or damaged GX340/GX390 heads. It suits those repairing pressure washers, portable generators, water pumps and similar equipment who want a ready-to-install solution that includes gaskets, hardware and setup tools to minimize downtime.