Blew #2 spark plug out of the head

[madhatter]

Was driving along, accelerating from a light, and BAM, CHUG CHUG CHUG. Lifted off, noise mostly stops. Limped the car home the 3 miles sounding like a tractor the whole way and put it in the air. Nothing below. Sound was coming from above, so i put my hand over the valve cover and felt air from the #2 coil. It was popped up. pulled the plugs and the threads on the cylinder head in #2 are toast.
Tried rethreading a new plug in, and it just put shavings into the cylinder. borescope confirmed. so it's off and staying off until i get that sorted, and i'll need to timesert or helicoil the hole. Ugh. anyone done this? any tips?

 

[SteveS]

Haven't done this myself, but a helicoil is not recommended for a boosted engine. According to Google,

The correct tool for a first-time thread repair on the 2018 Ford Fiesta ST (1.6L EcoBoost) is the Time-Sert M12x1.25 Extended Deep Hole Spark Plug Kit, Part Number 4212E. [1, 2]
Because modern EcoBoost engines feature deeply recessed, hard-to-reach spark plug wells, standard short kits will not reach the threads. The 4212E kit is specifically designed with extended tooling to safely reach down past 6 inches inside deep-well cylinder heads. [1, 2]

📦 Crucial Ordering Notes: Inserts are Sold Separately
Unlike standard automotive bolt kits, Time-Sert deep-hole spark plug kits do not include the thread inserts in the base tool box. You must order the correct inserts separately to match your exact spark plug style: [1, 2]

• Tapered Seat Inserts (Most Common for Ford): Part Number 42126 (21mm / .827 inch reach).
• Washer/Gasket Seat Inserts: If your replacement spark plugs use a crush washer rather than a smooth tapered seat, you will instead need washer seat inserts such as 42123 (15mm) or 42125 (17.5mm). Always look at your new spark plug's seating style before placing the order. [1, 2, 3]

🛠️ Important Installation Tips for This Kit

1. Flute Packing: When using the reamer and step-tap included in the kit, pack the valleys (flutes) of the cutting tools completely full of thick wheel bearing grease. Take the tool out every 2–3 turns, wipe away the trapped metal shavings, apply fresh grease, and repeat. [1]
2. Expansion Driver: The final tool in the kit is a cold-rolling driver tool. It mechanically expands the bottom threads of the steel insert against the aluminum head, locking it permanently into place so it can never back out when you change plugs in the future. [1, 2]
3. Use Thread Sealer: Be sure to apply the high-temperature liquid thread sealer (included or ordered as part number 6020) to the outer threads of the insert before driving it into the engine block. [1, 2]

It is uncommon to blow a spark plug out of this engine, but if it happens it's likely due to undertightening less than the factory spec of 17 Nm, allowing the plug to vibrate loose, or overtightening which damaged the threads, or cross-threading, which also damages the threads.

 

[madhatter]

these plugs have been in there a while, and i torqued them to 22 ft.lbs when i did them. this just ....blew. the #3 one was a PITA to get out as it was almost siezed. they have 52k miles on them. interval being 90k. thanks for posting the timesert link. need to do some reading on that.