Clarifying the Time-Sert 5600 Triple Oversized Repair: A Case of Mistaken Tap Sizes

We recently had a customer call us, that was understandably confused about a Time-Sert thread repair kit. He had purchased a different kit in effort to save money, a smaller less expensive M18x1.5 (Kit #1815), assuming that "M18x1.5" referred to the size of the tap needed for his blown-out spark plug hole.

Honestly, it’s a very easy mistake to make. If you pull the tap out of a standard M18x1.5 kit, it has M18x1.5 marked right on the tool. However, there is a massive technical difference between a standard M18x1.5 kit and a specialized Ford "triple oversized" kit. The 5600 does use what they call an oversize M18x1.5. They are not the same size.

The Problem: A Spark Plug Hole That’s Already Too Big

After talking with him for a few minutes to figure out what the issue was, he explained the history of the vehicle's cylinder head. This was a classic Ford modular engine spark plug blowout, a common problem we are far too familiar with on the 2-valve 4.6L, 5.4L, and 6.8L SOHC engines.

But, the spark plug hole had already had two previous failed repairs:

1. First Repair: A standard, parts-store thread insert. What we call temprary at best.

2. Second Repair: A shop later used a "double oversized" repair kit when the first one failed.

The customer’s logic was actually on the right track: he knew the hole was now massive, and he wanted to downsize the giant hole back to the original spark plug size. He thought he could use a standard M18x1.5 kit to create a new thread, screw in a smaller insert inside and solve the problem.

While his intuition was right, a standard M18 insert is not large enough for his parts store insert. The hole left behind by a failed double-oversized repair is massive. For a true triple-oversized repair, you need a kit engineered specifically for this extreme scenario. No need to re-invent the wheel, or in this case a triple oversize spark plug thread repair kit. The engineering has already been done and is proven.

The Solutions: Time-Sert 5600 vs. The Win Tools 389XL Kit

We have been selling Time Sert thread repair kits since 2005, and over the years, we’ve learned exactly what works best depending on your budget and preference. There are two definitive ways to permanently fix this issue:

Option 1: The Time-Sert 5600 Kit (The Dual-Insert Method)

For many years the Time-Sert 5600-389 has been the benchmark for the largest possible Ford spark plug repair.

• The Setup: Unlike a standard M18 kit, the M18 components in the 5600 kit are custom-engineered and uniquely oversized specifically to bite into a massive, failed double-oversized hole.

• How it Works: It uses a nested, two-insert system per hole. An oversized outer M18x1.5 insert locks into the newly reamed cylinder head and a second, smaller insert is installed inside that outer sleeve to bring the threads back down to the stock Ford spark plug size, M14x1.25.

Option 2: The 389XL Kit (The Single-Insert Alternative)

For a limited time, we also offer the Win Tools 389XL Extra Large Kit. This is a highly popular, cost-effective alternative to the 5600.

• Single Insert Design: Instead of nesting two inserts together, the 389XL uses one large, thick-walled solid steel sleeve.

• Line-up Guide: Similar to the popular CalVan 38900 style, it includes a mechanical line-up guide tool that perfectly centers the reamer inside the deep spark plug well—completely eliminating guesswork or crooked drilling and tapping.

Real Time-Savers: Verifying Closed Valves

When doing a repair like this, your valves must be completely closed before you start drilling or tapping so you don't accidentally hit a valve with tooling and ruin the cylinder head.

Time-Sert’s standard instructions suggest removing the valve cover to manually inspect the camshaft lobe positioning. Let's be honest: pulling a Ford modular valve cover just to check cam lobes is a huge pain. The good news is there is an easier way.

To save hours of teardown time, we offer these kits bundled with the 389-4000 Cylinder Leak Tester (and it comes standard in the 389XL kit).

• You simply pop the tester's rubber test tube type stopper into the spark plug well and hook up to compressor air.

• As you slowly turn the engine over by hand, the cylinder will build pressure the exact moment the valves close, instantly popping the stopper out. It is a massive real-time saver.

Why Buying From Us Matters (And a Warning About Online Knock-offs)

If you are unsure which thread repair kit is right for your specific application, give us a quick call before you buy. Spending a few minutes on the phone with us can prevent you from purchasing an incorrect or inferior kit.

⚠️ Buyer Beware: Be incredibly cautious of similar-looking kits listed on Amazon or eBay. For some reason, these platforms allow cheap, unbranded copies that are hard to distinguish from the real thing online. Using a low-quality, poorly machined knock-off tool and/or inserts inside an aluminum cylinder head is a recipe for catastrophic engine failure.

When you purchase an authentic kit from us, you aren't just getting the tools—you are getting our 20+ years of expertise. We include our own exclusive, compiled tip sheets with every order that answer the most common questions we've received since 2005. Best of all, if you read the instructions and our tips and still have a question mid-repair, we are typically available to pick up the phone and walk you through it.