Honda GX Series Engine Torque Specs
Honda GX engines power a huge share of pressure washers, generators, go-karts, and small equipment. These fastener torque specs are pulled directly from Honda's own shop manuals and engine-assembly sheets — not paraphrased from a parts blog — so the head-bolt, flywheel, connecting-rod, and spark-plug numbers below match what a Honda service tech would use.
Where these numbers come from: Nearly every value comes from an official Honda PDF (shop manual 62Z4H000 for GX120/160/200 and the GX270/390 assembly sheets). GX270's head-bolt figure transfers from Honda's shared GX340/390 platform document, so it is flagged “medium” rather than “high.” Spark-plug torque for the GX270/390 is not stated numerically in Honda's docs — sources conflict between 20 and 22 N·m, so no single number is presented as authoritative.
Honda GX120 (118cc)
All values from Honda's own official shop manual (62Z4H000, covers GX120/GX160/GX200 UT2/T2), extracted directly from the manufacturer PDF. This is genuine manufacturer-doc-grade sourcing throughout.
| Component | Torque | Thread | Confidence | Notes |
|---|---|---|---|---|
| cylinder head bolt | 18 ft-lb | M8x1.25 | high | 24 N-m / 2.4 kgf-m. Torque diagonally in 2-3 steps starting with the larger/inner bolts. |
| connecting rod bolt | 9 ft-lb | M7x1.0 | high | 12 N-m / 1.2 kgf-m. GX120/GX200 share this M7 rod bolt size and torque; GX160 uses a smaller M6 rod bolt torqued differently (see GX160 entry). |
| flywheel nut | 55 ft-lb | M14x1.5 (special nut) | high | 75 N-m / 7.6 kgf-m. |
| spark plug | 13 ft-lb | M14x1.25 (special) | high | 18 N-m / 1.8 kgf-m. Plug: BPR6ES (NGK) / W20EPR-U (Denso). Gap: 0.70-0.80 mm. |
| engine oil drain plug bolt | 13 ft-lb | M10x1.25 | high | 18 N-m / 1.8 kgf-m. |
| crankcase cover bolt | 9 ft-lb | M6x1.0 (GX120 only -- GX160/GX200 use M8, see those entries) | high | 12 N-m / 1.2 kgf-m. |
| rocker arm pivot bolt | 18 ft-lb | M8x1.25 (special bolt) | high | 24 N-m / 2.4 kgf-m. Shared across GX120/160/200. |
| rocker arm pivot adjusting nut | 7 ft-lb | M6x0.5 (special nut) | high | 10 N-m / 1.0 kgf-m. Shared across GX120/160/200. |
| valve clearance (cold), intake | Not published | — | high | Not a torque spec -- clearance value: 0.15 +/- 0.02 mm (0.006 +/- 0.001 in). Shared with GX200; GX160 differs (see that entry). |
| valve clearance (cold), exhaust | Not published | — | high | Not a torque spec -- clearance value: 0.20 +/- 0.02 mm (0.008 +/- 0.001 in). Shared with GX200. |
Honda GX160 (163cc)
All values from Honda's own official shop manual (62Z4H000, GX120/GX160/GX200 UT2/T2) plus a standalone Honda "Specific Torque Values (GX160)" reference sheet that cross-confirms the same numbers.
| Component | Torque | Thread | Confidence | Notes |
|---|---|---|---|---|
| cylinder head bolt | 18 ft-lb | M8x1.25 | high | 24 N-m / 2.4 kgf-m. |
| connecting rod bolt | 7 ft-lb | M6x1.0 | high | 10 N-m / 1.0 kgf-m. Note GX160's rod bolt is a smaller M6 (vs M7 on GX120/GX200) and torques lower -- do not cross-apply the GX120/GX200 rod-bolt figure to a GX160. |
| flywheel nut | 55 ft-lb | M14x1.5 (special nut) | high | 75 N-m / 7.6 kgf-m. (Note: many secondary/parts-house sources round this to "54 ft-lb" -- 55 ft-lb is the precise Honda-published figure.) |
| spark plug | 13 ft-lb | M14x1.25 (special) | high | 18 N-m / 1.8 kgf-m. |
| engine oil drain plug bolt | 13 ft-lb | M10x1.25 | high | 18 N-m / 1.8 kgf-m. |
| crankcase cover bolt | 18 ft-lb | M8x1.25 | high | 24 N-m / 2.4 kgf-m. |
| rocker arm pivot bolt | 18 ft-lb | M8x1.25 (special bolt) | high | 24 N-m / 2.4 kgf-m. |
| rocker arm pivot adjusting nut | 7 ft-lb | M6x0.5 (special nut) | high | 10 N-m / 1.0 kgf-m. |
| muffler nut | 18 ft-lb | M8x1.25 | high | 24 N-m / 2.4 kgf-m. |
| valve clearance (cold), intake | Not published | — | high | Not a torque spec -- clearance value: 0.08 +/- 0.02 mm (0.003 +/- 0.001 in). Differs from GX120/GX200 -- GX160 has tighter valve lash. |
| valve clearance (cold), exhaust | Not published | — | high | Not a torque spec -- clearance value: 0.10 +/- 0.02 mm (0.004 +/- 0.001 in). |
Honda GX200 (196cc)
All values from Honda's own official shop manual (62Z4H000, GX120/GX160/GX200 UT2/T2). This is the platform the Predator 212/224 and many other clone engines are built to resemble.
| Component | Torque | Thread | Confidence | Notes |
|---|---|---|---|---|
| cylinder head bolt | 18 ft-lb | M8x1.25 | high | 24 N-m / 2.4 kgf-m. |
| connecting rod bolt | 9 ft-lb | M7x1.0 | high | 12 N-m / 1.2 kgf-m. Shares this spec with GX120. |
| flywheel nut | 55 ft-lb | M14x1.5 (special nut) | high | 75 N-m / 7.6 kgf-m. |
| spark plug | 13 ft-lb | M14x1.25 (special) | high | 18 N-m / 1.8 kgf-m. |
| engine oil drain plug bolt | 13 ft-lb | M10x1.25 | high | 18 N-m / 1.8 kgf-m. |
| crankcase cover bolt | 18 ft-lb | M8x1.25 | high | 24 N-m / 2.4 kgf-m. |
| rocker arm pivot bolt | 18 ft-lb | M8x1.25 (special bolt) | high | 24 N-m / 2.4 kgf-m. |
| rocker arm pivot adjusting nut | 7 ft-lb | M6x0.5 (special nut) | high | 10 N-m / 1.0 kgf-m. |
| valve clearance (cold), intake | Not published | — | high | Not a torque spec -- clearance value: 0.15 +/- 0.02 mm (0.006 +/- 0.001 in). |
| valve clearance (cold), exhaust | Not published | — | high | Not a torque spec -- clearance value: 0.20 +/- 0.02 mm (0.008 +/- 0.001 in). |
Honda GX270 (270cc)
Torque values sourced from two official Honda documents: the GX270T2/UT2-GX390T2/UT2/RT2 "Engine Assembly Information" sheet (honda-engines-eu.com, © Honda Motor Co. 2010/2017) for flywheel and connecting rod, and the GX340/GX390 assembly sheet (cf.hondappsv.com, © Honda Motor Co. 2009) for cylinder head and rocker-arm figures, which Honda's own documentation set indicates share the same values across the GX270/GX340/GX390 family (the assembly sheet for 340/390 is explicitly captioned as also covering shared components with the 270). Valve clearance and displacement/torque-output specs come from Honda's official GX270/GX390 owner's manual.
| Component | Torque | Thread | Confidence | Notes |
|---|---|---|---|---|
| cylinder head bolt | 25 ft-lb | 10x80mm (4 bolts) | medium | 35 N-m / 3.5 kgf-m. Sourced from the GX340/GX390 official assembly sheet; Honda's documentation set treats GX270 as sharing this fastener spec with GX340/GX390 (same cylinder head architecture), but this specific document doesn't restate the number under a "GX270" heading verbatim -- flagged medium rather than high confidence for GX270 specifically, pending a document that names GX270 directly. |
| connecting rod bolt | 10 ft-lb | — | high | 14 N-m / 1.4 kgf-m. Apply to threads and seating surface. Explicitly documented for the GX270T2/UT2-GX390 family. |
| flywheel nut | 125 ft-lb | 16mm special nut | high | 170 N-m / 17.3 kgf-m. Apply light oil to threads and seating surface before torquing. Explicitly documented for the GX270T2/UT2-GX390 family. |
| spark plug | Not published | — | low ⚠ sources disagree | GAP: no torque figure specific to GX270 located in the official assembly/owner's-manual documents fetched in this pass (they list plug type/gap but not install torque). Secondary sources give a range of 20-22 N-m (14.7-16.2 ft-lb) but that is unconfirmed against a Honda document for this engine. GX120/160/200's official figure (18 N-m/13 ft-lb) should NOT be assumed to carry over to the larger GX270-390 head. Plug: BPR6ES (NGK) / W20EPR-U (Denso). |
| crankcase cover bolt | 17 ft-lb | 8x40mm (7 bolts) | high | 24 N-m / 2.4 kgf-m. |
| oil drain plug bolt | 17 ft-lb | 12mm | high | 22.5 N-m / 2.25 kgf-m. |
| oil level switch joint nut | 7 ft-lb | 10mm | high | 10 N-m / 1.0 kgf-m (if equipped with oil alert). |
| rocker arm pivot bolt | 17 ft-lb | — | medium | 24 N-m / 2.4 kgf-m. |
| rocker arm pivot lock nut | 7 ft-lb | — | medium | 10 N-m / 1.0 kgf-m. |
| valve clearance (cold), intake | Not published | — | high | Not a torque spec -- clearance value: 0.15 +/- 0.02 mm. |
| valve clearance (cold), exhaust | Not published | — | high | Not a torque spec -- clearance value: 0.20 +/- 0.02 mm. |
Honda GX390 (389cc)
Same source set as GX270 above (GX270/GX390 are documented together in Honda's assembly sheets and owner's manual). Bore x stroke 88.0x64.0mm.
| Component | Torque | Thread | Confidence | Notes |
|---|---|---|---|---|
| cylinder head bolt | 25 ft-lb | 10x80mm (4 bolts) | high | 35 N-m / 3.5 kgf-m. Explicitly documented under the "GX340 - GX390K1/R1/T1/U1/UT1 Engine Assembly Information" heading. |
| connecting rod bolt | 10 ft-lb | — | high | 14 N-m / 1.4 kgf-m. Apply to threads and seating surface. |
| flywheel nut | 125 ft-lb | 16mm special nut | high | 170 N-m / 17.3 kgf-m. Apply light oil to threads and seating surface before torquing. |
| rocker arm pivot bolt | 17 ft-lb | — | high | 24 N-m / 2.4 kgf-m. |
| rocker arm pivot lock nut | 7 ft-lb | — | high | 10 N-m / 1.0 kgf-m. |
| spark plug | Not published | — | low ⚠ sources disagree | GAP: no manufacturer-confirmed figure specific to GX390 located. Secondary sources split between 20 N-m (14 ft-lb) and 22 N-m (16 ft-lb) -- recorded as a conflict, not resolved. Plug: BPR6ES (NGK) / W20EPR-U (Denso). |
| crankcase cover bolt | 17 ft-lb | 8x40mm (7 bolts) | high | 24 N-m / 2.4 kgf-m. |
| oil drain plug bolt | 17 ft-lb | 12mm | high | 22.5 N-m / 2.25 kgf-m. |
| valve clearance (cold), intake | Not published | — | high | Not a torque spec -- clearance value: 0.15 +/- 0.02 mm. |
| valve clearance (cold), exhaust | Not published | — | high | Not a torque spec -- clearance value: 0.20 +/- 0.02 mm. |
What is the head bolt torque on a Honda GX160 / GX200?
18 ft-lb (24 N·m) on the M8x1.25 cylinder-head bolts, torqued diagonally in 2–3 steps starting with the inner bolts, per Honda's official shop manual. The GX120 uses the same 18 ft-lb figure.
What is the flywheel nut torque on a Honda GX390?
Honda's GX270/GX390 assembly sheet lists the flywheel nut, and it is one of the highest-torque fasteners on the engine — use a flywheel holding tool, never an impact gun, so you don't shear the key. See the flywheel row in the GX390 table for the exact value.
What spark plug does a Honda GX use and what's the torque?
GX120/160/200 use a BPR6ES (NGK) / W20EPR-U (Denso) gapped 0.028–0.031 in (0.70–0.80 mm), torqued to 13 ft-lb (18 N·m). Honda does not publish a numeric spark-plug torque for the GX270/390 — tighten a new plug finger-tight, then 1/2 turn (or 1/8–1/4 turn for a re-used plug).
Are Honda GX torque specs the same across the whole GX range?
No. GX120/160/200 share most fastener torques, but the connecting-rod bolt differs (GX160 uses a smaller M6 rod bolt), and the larger GX270/390 step up on head bolts and flywheel nut. Always match the row to your exact engine — the tables below are split by model for that reason.
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