Cylinder Head Components for Honda GX Engines

Hard starting, low compression, or a tick from the valve cover usually traces back to the cylinder head. This collection covers cylinder head components for GX160 through GX390 engines: complete head assemblies, intake and exhaust valve sets, push rods, rocker arms, valve springs, and head covers. Tell us your engine model and symptom at 301-519-9274 and we will point you at the right part instead of the whole pile.

Diagnosing Cylinder Head Problems on a GX Engine

The GX family powers most gas pressure washers, and the top end is where wear shows up first. Before you order parts, figure out which of three failures you have.

Valve trouble

Burnt or worn valves stop sealing, compression drops, and the engine gets hard to pull over or will not stay running under load. Popping back through the carburetor points at the intake valve. Popping out the muffler points at the exhaust valve. A compression test or a leak-down test settles it fast. Valve sets for these engines run under twenty dollars, so if the seats in the head are still clean, new valves plus a lash adjustment is the cheap fix.

Bent push rods and rocker wear

A push rod bends when a valve sticks or the engine floats the valves at overspeed, often after a governor problem or a stuck decompression system. The giveaway is a dead cylinder with a quiet rocker. Pull the head cover and roll the engine over by hand. Both rockers should move. Push rods are a two or three dollar part, but always find out why the rod bent or the new one bends too.

When to replace the whole head

Cracked castings, stripped spark plug threads, worn valve guides, and hammered valve seats are not worth fighting on an engine this cheap to fix. A complete head assembly arrives with valves, springs, and guides already installed and set. You torque it on, set lash, and go back to work. At $117 to $160 for the assembly, it beats a machine shop bill every time.

Symptom Lookup

Prices can change. Availability varies by part, so call to confirm before you tear the engine down.

Specs Worth Writing Down

Valve lash on GX engines: intake 0.15mm plus or minus 0.02 (about 0.006"), exhaust 0.20mm plus or minus 0.02 (about 0.008"), set cold at top dead center on the compression stroke. Head bolt torque on the GX240 through GX390 is 35 Nm, which is 25 ft-lb, pulled down in a cross pattern. Always fit a new head gasket when the head comes off. Reusing the old one is how a $10 job becomes a second teardown.

From the Field

Most of the head work we see walks in as a no-start after the machine sat all winter with old fuel. Varnish glues a valve open, the engine cranks with no compression, and the owner assumes the engine is done. It is usually a morning of work: pull the head, clean the valve, lap it in, new gasket, set lash. The other repeat offender is a leaking valve cover that the owner keeps topping off instead of fixing. Low oil on a splash-lubed engine kills the bottom end, and no head part fixes that. A nine dollar cover beats a $600 engine.

Related Collections

• All Engine Parts
• Head Gaskets
• Gasket Kits
• Camshaft and Crankshaft Parts
• Carburetor Components
• Honda Parts
• Engine Air Filters
• Recoil Start Assemblies
• Muffler Accessories
• Fan Cover Shrouds

Near Gaithersburg? Bring the head to our counter on Oakmont Ave and we will look it over with you.

Frequently Asked Questions

Why does my GX390 crank but have no compression?

Nine times out of ten a valve is stuck open, either from fuel varnish after storage or a bent push rod. Pull the valve cover and watch both rockers while you turn the engine by hand. If a rocker never moves, follow that push rod down.

What is the valve clearance on Honda GX engines?

Intake 0.15mm and exhaust 0.20mm, each with 0.02mm of tolerance, set cold at top dead center on compression. Loose lash makes a ticking noise. Tight lash burns valves. Check it any time the head has been off.

Is it cheaper to rebuild my cylinder head or replace it?

If the casting, guides, and seats are good, a valve set under $20 plus a gasket does it. If the head is cracked, the guides are sloppy, or the plug threads are stripped, a complete assembly at $117 to $160 is cheaper than machine work.

What makes push rods bend on these engines?

Sticking valves, overspeed valve float, or interference from a failed decompression mechanism. The rod is the fuse, not the fault. Replace it, then find out what stopped the valve or you will bend the next one.

How tight do the head bolts go?

35 Nm, or 25 ft-lb, on GX240 through GX390 heads, torqued in a cross pattern on a new gasket. Do not guess with an impact gun. An overtightened bolt strips the block threads and turns a head job into an engine job.

Do GX340 and GX390 share head parts?

Many top end parts interchange between the two, which is why our push rods, valve sets, and covers list as GX340-390. Head assemblies are model specific. Check your engine's stamped model code before ordering.