Briggs & Stratton 31R907-0007-G1 500cc 17.5 Gross HP Engine
✅ PROS
- Drop-in replacement for many Briggs 31R9-series engines — same bolt pattern and shaft size
- Cast iron bore and dual ball bearings deliver long service life under heavy mowing
- Comes with muffler, air filter, and fuel tank — ready to bolt on
❌ CONS
- Recoil start is stiff on cold mornings; some users report needing 3-4 pulls
- No fuel shutoff valve — small issue if you store long-term
- Genuine Briggs parts cost more than aftermarket equivalents
The Verdict
Bottom line: This is the engine that keeps your mower alive when the original dies. The Briggs & Stratton 31R907-0007-G1 is a 500cc, 17.5 gross HP vertical-shaft workhorse, and at 4.6 stars from 229 buyers, it earns its reputation. You’re paying for reliability, not flash.
What you actually get
Open the box and you’ll find the complete engine: the 500cc overhead-valve block, a muffler, air filter assembly, 1.5-quart fuel tank, and a recoil start mechanism. The shaft is a standard 1-inch diameter by 3.19 inches long — that’s the exact spec for hundreds of riding mowers and lawn tractors from MTD, Troy-Bilt, and Craftsman. If your old engine is a 31R907 or similar, this bolts on with no modifications.
The 3.44-inch stroke and 3.12-inch bore give you 17.5 gross HP at 3,600 RPM. That’s enough grunt for a 42-inch deck cutting thick, damp grass. The cast iron bore liner and full-pressure lubrication (with a spin-on oil filter) are the heavy-duty details that separate this from cheaper engines.
Real-world performance
Owners consistently report it fires up and performs like a factory replacement. One verified buyer wrote: “Put it on a 2008 Troy-Bilt pony. Bolted right up, started on the second pull, and it’s been cutting for two seasons now.” Another noted: “The power difference vs. my old 15.5 HP is noticeable — it doesn’t bog down in tall grass.”
The overhead valve design runs cooler and cleaner than older L-head engines, which means less valve maintenance. The dual ball bearings on the crank shaft reduce vibration, so you’ll feel less shake in the steering wheel at full throttle. Fuel consumption is typical for this class — roughly 0.5 gallons per hour under load, so the 1.5-gallon tank gets you about three hours of mowing.
What buyers praise
The dominant theme in reviews: ease of installation. Multiple users mention it’s a direct swap. One review said: “I’m not mechanically inclined. This took me an afternoon with basic wrenches. Everything lined up.” The cast iron bore gets consistent shout-outs for longevity — buyers expect 1,500+ hours of service. The included components (muffler, tank, filter) also save you $50-80 in parts you’d otherwise need to source separately.
Where it falls short
Three honest complaints surface repeatedly. First, the recoil starter is stiff when cold — several buyers mention needing a firm, deliberate pull, and one user with a bad shoulder found it genuinely difficult. Second, there’s no fuel shutoff valve, which means you’ll want to drain the carburetor or run it dry before winter storage, or you risk gummed-up jets. Third, genuine Briggs parts (like the air filter and oil filter) cost 20-30% more than aftermarket — but they fit perfectly and last longer, so I consider that a fair trade.
One more note: this engine is not a zero-turn or pressure-washer unit. It’s a vertical-shaft, horizontal-crank design strictly for ride-on mowers and tractors. If you need a horizontal shaft for a log splitter or go-kart, look elsewhere.
Who should buy this
- DIY mower owners with a dead 31R9-series engine who want a guaranteed fit
- Owners of 2005-2015 MTD, Troy-Bilt, Craftsman, or Cub Cadet tractors — this is the most common replacement for that generation
- Anyone tired of rebuilding an old engine — new costs less than the labor and parts for a rebuild
Skip it if you need a horizontal shaft, or if you’re on a tight budget — aftermarket clones like the Predator 420cc run about $100 less, but you’ll lose the cast iron bore and factory support.
FAQ
Q: Will this fit my 42-inch Craftsman mower?
A: Check your old engine’s model number. If it starts with 31R9 (like 31R907), yes — this is the direct replacement. The 1-inch by 3.19-inch shaft fits most 42-inch deck spindles.
Q: Does it come with a wiring harness or key switch?
A: No. You’ll reuse your existing wiring and key switch. It has a standard 12V charging system with a flywheel magneto, but the plug is a simple two-wire connector.
Q: How hard is the first start?
A: Prime the bulb 3-4 times, set the choke, and pull. Most buyers get it on the first or second pull. On cold days, expect a stiffer pull — that’s the compression release working.
The Verdict
Buy it if you want a drop-in replacement that will outlast your mower. The cast iron bore, dual ball bearings, and full-pressure lube make this a genuine 10-year engine.
Skip it if you’re restoring a classic tractor for show (you’ll want a period-correct engine), or if you’re mechanically timid — this is a straightforward install, but it’s not a 30-minute job.
Rating: 4.6/5 — loses half a star for the stiff recoil and missing fuel shutoff. Everything else earns its keep.
Briggs & Stratton 31R907-0007-G1 is the right call for anyone who values reliability over the cheapest price. It’s the engine your mower deserves.
Where to Buy
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Last updated: 2026-08-06. Ratings and prices current as of review date. Verify on Amazon before purchasing.