Briggs & Stratton 31R907-0007-G1 500cc 17.5 Gross HP Engine with 1-Inch by 3-5/32-Inch Length Crankshaft Tapped 7-16-20-Inch Review

Overview

The Briggs & Stratton 31R907-0007-G1 is a replacement or custom-build engine, not a complete lawn mower. It’s a 500cc, 17.5 gross HP powerplant designed for riders, zero-turns, or heavy-duty walk-behinds that need a reliable, no-nonsense horizontal shaft engine. If you’re rebuilding an older mower, upgrading a tired power unit, or fabricating a custom rig, this engine delivers proven torque and a simple, serviceable design. It’s best for mechanically inclined homeowners, small property owners (1–3 acres), and DIY landscapers who want a drop-in workhorse without electronic complexity.

Who Should Buy This

Rebuilders and Restorers – If you’ve got a classic John Deere, Craftsman, or MTD rider with a blown engine, this is a direct-fit replacement. The 1-inch by 3-5/32-inch crankshaft with a 7/16-20 tapped hole matches many common pulley and blade configurations.

Homeowners on 1–2 Acres – You don’t need a commercial engine, but you want something that starts reliably and pulls through thick grass without bogging. This 500cc unit gives you ample grunt for hilly or damp turf.

DIY Fabricators – Building a go-kart, log splitter, or custom power tool? The 17.5 HP rating and standard shaft size make this a versatile power source for projects beyond mowing.

Budget-Conscious Upgraders – You’d rather spend $732 on a new engine than $1,500+ on a whole new mower. This is a cost-effective path to extend the life of a solid chassis.

Key Features Breakdown

500cc Displacement / 17.5 Gross HP – Bigger displacement means more torque at lower RPMs. This engine doesn’t need to scream to cut through wet or tall grass; it lugs down and keeps pulling. That translates to less strain and longer life.

1-Inch by 3-5/32-Inch Crankshaft, Tapped 7/16-20 – This is a standard SAE shaft size for many lawn tractors and zero-turns. The tapped end lets you bolt on pulleys or blades with a single fastener. Measure your existing shaft before buying—most riders use this exact spec.

Horizontal Shaft Design – Unlike vertical shaft engines (common on push mowers), this one mounts with the shaft parallel to the ground. It’s the standard for riders and tractors. The mounting pattern is typically a 4-bolt flange, but check your chassis’ bolt spacing.

No Electronic Fuel Injection (EFI) – This is a carbureted engine. That’s a pro for some (easier to work on, no expensive sensors) and a con for others (cold starts, ethanol fuel issues). Plan for a fuel stabilizer or non-ethanol gas.

Recoil and Electric Start Ready – The engine comes with a starter and alternator charging system (typically 3-5 amps). You’ll need a battery and ignition switch to use electric start, but it’s prewired for simplicity.

Pros

Proven Reputation – Briggs & Stratton has been making small engines for over a century. Parts are everywhere, and any small engine shop can service this. No waiting for proprietary components.

Torque for Days – The 500cc displacement punches above its HP rating. It’ll spin a 42- or 48-inch deck without hesitation, even in thick St. Augustine or wet fescue.

Simple Carburetor Design – No ECM, no throttle-body sensors. If it sits all winter, you can clean the carb in 30 minutes with basic hand tools. A rebuild kit costs under $15.

Direct Replacement Fit – For most popular lawn tractors (Craftsman, Husqvarna, MTD, Troy-Bilt), this engine bolts in with no adapter plates. The shaft length and diameter match OEM specs.

Great Value – At $732, it’s roughly half the cost of a comparable Kawasaki or Kohler engine. You lose some refinement but gain a massive parts network and lower upfront cost.

Electric Start Included – No pull-start frustration. Hook up a battery and you’ve got key-turn convenience. The built-in alternator keeps the battery charged.

Cons

Carburetor Tuning Can Be Fussy – Out of the box, some units need the idle mixture adjusted. If you’re not comfortable turning a screwdriver, budget for a shop to dial it in. Also, ethanol fuel will gum it up fast—use stabilizer or non-ethanol gas.

Not a Premium Brand – This is a workhorse, not a racehorse. It’s louder and vibrates more than a Kawasaki or Kohler. If you want silky smooth operation and whisper-quiet run, spend more.

Parts Availability Varies – While common parts are everywhere, some internal components (like the camshaft or governor gear) can be backordered. For most users, this isn’t an issue, but it’s worth noting.

No Warranty Support from Amazon – You’re buying through a third-party seller. If the engine arrives damaged or fails early, you’re dealing with the seller, not Briggs directly. Check return policies carefully.

Bottom Line

The Briggs & Stratton 31R907-0007-G1 is the engine equivalent of a reliable pickup truck—it’s not flashy, but it gets the job done. If you’re mechanically comfortable with basic carburetor maintenance and need to breathe new life into a mower chassis you already love, this is a smart, affordable choice. The 500cc displacement delivers real grunt for 1–2 acre properties, and the standard shaft size means it’ll fit most lawn tractors and zero-turns. Skip it if you want a whisper-quiet, maintenance-free experience—that’s not this engine’s game. But for a DIY rebuild or a budget-friendly replacement, it’s a solid 4.5-star buy.

Frequently Asked Questions

Does this engine come with a muffler, air filter, and fuel tank?
Yes, it includes a muffler, air filter, and fuel tank. However, the fuel tank may be a plastic, top-mount style that requires clearance. Check your chassis dimensions—some older tractors have tight hood clearance.

Will this fit my Craftsman LT1000 or Husqvarna YTH22V46?
Probably yes. Both models use a 1-inch by 3-5/32-inch crankshaft with a 7/16-20 tapped hole. The mounting pattern is the standard 4-bolt flange. Measure your old engine’s bolt pattern (center-to-center) to confirm—most are 4.5 inches wide and 3.5 inches deep.

Do I need to adjust the governor or carburetor out of the box?
Often yes. The engine is