Stripped Spark Plug Threads: The $38 Fix, Not a New Head
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Pricing note: the prices and availability in this article are accurate as of July 2026 and are subject to change. Always check the retailer’s current price before buying.
It is one of the most common ways a small engine ruins your afternoon: you go to change the spark plug, the plug comes out with a little too much aluminum attached, and the threads in the head are stripped. The first reaction is almost always the wrong one. People assume a stripped spark plug hole means a new cylinder head. An owner faced exactly that choice on My Tractor Forum, weighing a thread insert against replacing the head on a Briggs engine (head 898807). The honest answer for most engines is a $30 to $40 thread-repair kit and fifteen careful minutes, not a new head.
Summary
Stripped spark plug threads on the vast majority of small engines (Briggs, Kohler, Honda, Kawasaki, Tecumseh) are an M14 × 1.25 thread, and one repair kit fits most of them. For a first-time, light-duty repair, the Heli-Coil 5334-14 complete kit (about $38 at O’Reilly) is the right answer: tap, inserts, and install tool in one box. For an aluminum head under heavy heat cycling, a Time-Sert 4412 ($80 to $150) gives a more robust solid insert. A new head (Briggs 898807, $80 to $200+) is only worth it if the head is otherwise damaged. Start with the Heli-Coil unless you have a specific reason not to.
What the repair actually is
A spark plug screws into soft aluminum threads in the cylinder head. Aluminum is easy to cross-thread and easy to strip, especially if a plug was over-tightened or installed at an angle once in the past. A thread repair does not patch the old threads. It cuts the damaged hole oversize with a tap, then installs a steel insert that gives you fresh, stronger threads in the same spot. The plug then threads into steel instead of tired aluminum, which is often better than the factory threads were.
The two main approaches differ in what the insert is. A Heli-Coil is a coiled wire insert. A Time-Sert is a solid, one-piece threaded bushing. Both work. They sit at different points on the cost-and-robustness curve, which is what the decision tree below is about.
What it fits
Fits: M14 × 1.25 spark plug threads, which is the standard on most small engines and a great many automotive applications. That covers Briggs, Kohler, Honda, Kawasaki, and Tecumseh small engines as a rule. The source thread was a Briggs head numbered 898807, but the repair itself is not engine-specific. Check that your spark plug is M14 × 1.25 (most are), and one kit covers the job. If your engine uses a different plug thread, buy the kit that matches that thread instead.
The part numbers worth knowing
There is a small thicket of numbers here because the same repair is sold by several brands and in several configurations (complete kit, inserts only, tap only). The useful ones:
- Heli-Coil 5334-14 / 533414: the complete spark-plug kit (tap, inserts, install tool). Same kit, different distributor numbering.
- Heli-Coil 5396-14 Sav-A-Thread HT: the version marketed for Ford 5.4/4.6L, identical thread spec.
- Heli-Coil R5326-14N: Sav-A-Thread inserts only, no tools. For when you already own the tap.
- Heli-Coil 5332-14: the tap by itself. Pairs with loose inserts.
- Briggs & Stratton 100013: B&S-branded Heli-Coil-equivalent. Useful if you want the engine maker’s own blessing on the fix.
- NAPA Fix-A-Thred BK-98141: a generic budget alternative.
- Time-Sert 4412 (and the GM-spec variant 4412S-187): the premium solid-insert kit.
All of these are M14 × 1.25 for the spark-plug-hole application, so they are interchangeable in the sense that any of them solves the same problem. The choice is about kit completeness and how robust you need the result to be.
The decision tree
First-time repair, light-duty engine: Heli-Coil 5334-14 (~$38)
For a mower, a generator, a garden tractor, or any light-duty small engine, the complete Heli-Coil kit is the right starting point. It comes with everything you need in one box, the coiled insert is plenty strong for these applications, and it is the most beginner-friendly of the options. The Heli-Coil 533414 at O’Reilly runs about $38.99 with in-store pickup, which beats waiting on shipping when your mower is in pieces.
Aluminum head, high heat or high load: Time-Sert 4412 ($80 to $150)
If the head runs hot and cycles hard, or you simply want the most robust repair available, the Time-Sert solid insert is the upgrade. It is a one-piece threaded bushing rather than a coil, which many people prefer in aluminum heads under repeated heat cycling. It costs more and the kit is an investment, but it is the choice when you want to do this once and never think about it again. Source it from Time-Sert directly or Wise Auto Tools.
Tight budget, you already own a tap: inserts only ($4 to $12)
If you have done this before and own the tap, you do not need another complete kit. Loose inserts (Heli-Coil R5326-14N, or multi-packs) run a few dollars on eBay, and the standalone tap (5332-14) is cheap too. This is the path for someone stocking inserts as a consumable, not someone doing their first repair.
Head is otherwise damaged: new head (Briggs 898807, $80 to $200+)
Replacing the head is the most expensive and most labor-intensive option, and it is only the right call if the head has other damage: a crack, a warped sealing surface, valve-seat trouble. A stripped spark plug hole on an otherwise good head is not a reason to buy a head. Thread repair exists precisely so you do not have to.
| Option | Price | What you get | When to use it |
|---|---|---|---|
| Heli-Coil 5334-14 kit | ~$38 | Tap, inserts, tool, all-in-one | First-time, light-duty. The default. |
| NAPA Fix-A-Thred BK-98141 | ~$25-$35 | Budget generic kit | Cheaper all-in-one alternative |
| Briggs 100013 | ~$35-$50 | B&S-branded coil kit | Want the engine maker’s own kit |
| Time-Sert 4412 | $80-$150 | Solid one-piece insert kit | Aluminum head, high heat/load |
| Inserts only (R5326-14N) | $4-$12 | Just the coil inserts | You already own the tap |
| New head (898807) | $80-$200+ | Whole cylinder head | Only if the head is otherwise damaged |
Prices above are approximate and accurate as of July 2026, subject to change. Confirm the current price at the retailer before buying.
Where to buy it
eBay is the right place for individual pieces. As of the July 2026 check, listings ran from a few dollars for single inserts up into the hundreds for full professional sets, with a median around $50. You can find the 5332-14 tap on its own and packs of inserts cheaply, which is exactly what the stocking-up reader wants. For a first repair, though, the complete O’Reilly Heli-Coil kit at $38.99 is still the cleaner recommendation, because the all-in-one box means you are not gambling that the loose tap and loose inserts you bought separately actually match.
- Heli-Coil 5334-14 complete kit on Amazon: the all-in-one kit; check current price.
- Heli-Coil M14 components on eBay: taps and inserts individually, for the reader who already owns the tap or stocks inserts.
- Heli-Coil 533414 at O’Reilly: about $38.99, in-store pickup. The recommended first kit.
- NAPA Fix-A-Thred BK-98141: the budget alternative.
Tools needed
- The thread-repair kit (tap, inserts, install tool). A complete kit has all three.
- A tap wrench or ratchet to turn the tap.
- Grease for the tap flutes, to catch aluminum chips.
- Compressed air or a shop vac, and a spark plug socket.
The one thing that ruins this repair
Aluminum chips falling into the cylinder. When you tap the hole, the cutting action makes metal shavings, and you do not want those landing on top of the piston. Two habits prevent it. First, pack the tap’s flutes with grease so the chips stick to the tap instead of dropping in. Second, before you start, bring the piston up so the valves are closed and the chamber is as sealed as it can be, and afterward blow the area out and turn the engine over by hand with the plug out to push any stragglers up before you fire it. Go slow, back the tap out often to clear chips, and keep the tap square to the hole. The repair is genuinely easy; the chips are the only thing that bites people.
Heli-Coil or Time-Sert: the honest version
You will find strong opinions on both sides, and the truth is undramatic. For a light-duty small engine, a Heli-Coil is fully adequate and many of them outlast the engine. The Time-Sert’s solid insert is the better choice when the head is aluminum and runs under sustained heat and load, where some people prefer not to rely on a coil. It costs two to four times as much. If you have a single mower to fix and no special concerns, the Heli-Coil is not a compromise, it is the sensible pick. If you fix engines regularly or the head is a hard-working one, the Time-Sert earns its price. Neither is a trick; they are two reasonable points on the same curve.
Related on GetPartFound
- Lawn Boy recoil spring snapped? The $5 Stens 155-051 fix: another small-engine repair that looks worse than it is.
- Lawn Boy and Toro traction cable (92-6518): fix the part that failed, not the assembly around it.
The takeaway
- Stripped spark plug threads on most small engines are M14 × 1.25, and one kit fixes the job.
- Default answer: the complete Heli-Coil 5334-14 kit, about $38 at O’Reilly.
- Aluminum head under heat and load: step up to the Time-Sert 4412 ($80 to $150).
- Already own the tap? Buy inserts only for a few dollars.
- A new head (Briggs 898807, $80 to $200+) is only worth it if the head is otherwise damaged.
- Pack the tap with grease and keep the chips out of the cylinder. That is the whole skill.
A stripped spark plug hole sounds like the end of an engine. It is usually a thirty-eight dollar kit and the steadiest fifteen minutes you will spend all week.