PowerBuilt 31C707 500cc OHV Vertical Shaft Engine - Specs, Service Data, and Repower Guide
The 25.5 ft-lb PowerBuilt 31C707 - the 500cc OHV single fitted to a generation of big-box riders and lawn tractors.
Variant: 500cc PowerBuilt single, electric start
Specs last verified Oct 28, 2026 against the sources shown.
Dimensions
Our own illustrative drawing, from the published overall dimensions - not to scale.
Width (front to back in this view): 15.5 in (Briggs & Stratton). Leave clearance on the recoil side for the pull start.
Diagrams on this site are our own illustrative drawings, drawn from published dimensions (Briggs & Stratton) - not official or technical drawings. Verify dimensions before fitment.
How it stacks up
Against the engines it is most often compared with.
Full specifications
Specifications grouped by system.
01 Engine
- Bore x Stroke90.5 x 77.8 mm (Briggs & Stratton)
- ConfigurationOHV, single cylinder, vertical shaft, cast-iron cylinder sleeve, electric start (Briggs & Stratton)
- Displacement500 cc (Briggs & Stratton)
- Power17.5 gross HP (Briggs & Stratton)
- Torque25.5 ft-lb gross torque (Briggs & Stratton)
02 Dimensions and Mounting
- Dry weight65.0 lb (Briggs & Stratton)
- MountingBriggs single-cylinder rider base pattern (Briggs & Stratton)
- Height12.9 in (Briggs & Stratton)
- Length18.9 in (Briggs & Stratton)
- Width15.5 in (Briggs & Stratton)
03 Capacities and Service
- Oil capacity48 oz (1.5 qt), with filter (Briggs & Stratton)
04 Shaft and Fitment
- KeywayKeyway, crankshaft end tapped 7/16-20 (Briggs & Stratton)
- Shaft diameter1 in (Briggs & Stratton)
- Shaft length3-5/32 in (Briggs & Stratton)
Service data
Service specifications for rebuilds and tune-ups.
- Valve clearance - intake0.003-0.005 in (Briggs & Stratton)
- Valve clearance - exhaust0.005-0.007 in (Briggs & Stratton)
- Cylinder head bolt torque220 lb-in (Briggs & Stratton)
- Flywheel nut torque100 lb-ft (Briggs & Stratton)
- Spark plug gap0.030 in (Briggs & Stratton)
- Spark plug491055 (resistor spark plug) (Briggs & Stratton)
- Air filter796031 (Briggs & Stratton)
- Oil typeSAE 30 / SAE 10W-30 (Briggs & Stratton)
Service figures are for this model stamp as published - check your operator manual before a rebuild.
Find and decode your stamp
This engine's stamp reads: Model 31C707, Type 3026-G5, the Code is stamped per engine and gives its build date.
On these OHV singles the Model-Type-Code is stamped into the overhead valve (rocker) cover - check there first. Some builds also carry the same numbers stamped on the blower housing or on a metal tag attached to the housing. The numbers are shallow stampings and are often hidden under grass and oil film; wipe the cover clean and read them at an angle before ordering parts. (Verified against Briggs & Stratton operator-manual engine diagrams, which label the Model-Type-Code at the valve cover, and dealer identification guides.). Bring the full stamp - model, type, and code - to the decoder.
Read the PowerBuilt decode page or paste the whole stamp into the Briggs & Stratton decoder for the build date and what each part means.
Repower - what it replaces
Same rider footprint class as the Briggs Intek singles; the swap is decided by shaft size, crankshaft length, and bolt pattern, not by the badge on the cover.
Same footprint class as:
Common uses
Quick answers
How much oil does the PowerBuilt 31C707 take?
48 oz (1.5 qt) with an oil filter fitted, 42-44 oz without (Briggs & Stratton operator manual). Use SAE 30 or 10W-30 detergent oil and check the level on the dipstick with the engine level.
What are the valve clearances on the 31C707?
Intake 0.003-0.005 in and exhaust 0.005-0.007 in, checked cold (Briggs & Stratton repair manual 276781, Model 310000 Vertical Series). Set them with the piston 1/4 in past top dead center on the compression stroke.
What spark plug and gap does the 31C707 use?
Briggs & Stratton resistor plug 491055, gapped to 0.030 in and torqued to 180 lb-in (Briggs & Stratton operator manual and repair manual 276781).
What is the cylinder head bolt torque on the 31C707?
220 lb-in, tightened in stages in a cross pattern with a new head gasket (Briggs & Stratton repair manual 276781, Model 310000 Vertical Series). The flywheel nut is 100 lb-ft.
How much torque does the PowerBuilt 31C707 make?
25.5 ft-lb of gross torque (Briggs & Stratton 2011 European engine catalog, Series 4 PowerBuilt). Gross ratings follow SAE J1940; installed power in a mower will be lower.
Where is the model number on a PowerBuilt 31C707?
The full Model-Type-Code is stamped into the overhead valve cover on these OHV singles (some builds also carry it on the blower housing). One documented build of this model is Type 3026-G5 - match all three groups when ordering parts.