Probably The Costliest Mistake of My Life — Long Story Short, I Tried Replacing Spark Plugs Myself

One of the worst things any car owner can do while DIY maintaining or repairing their car is accidentally allowing a foreign object to fall inside the engine. Foreign objects such as dirt, sand, screws, sockets, etc., can and do occasionally fall into the engine either through the oil fill hole, an open carburetor while the air filter is off (in older model cars), or into a radiator with its cap temporarily laid aside.

However, one of the more likely scenarios of a foreign object winding up in the engine is when the spark plugs are changed, and the cylinder head spark plug openings become a costly accident waiting to happen.

Why Debris in a Cylinder is a Serious Problem

If Debris falls into the cylinder through the spark plug hole during a spark plug change, it can cause significant damage to the engine if the Debris is not removed. Damage such as:

1. Scoring or Scratching of Cylinder Walls—Damage to the cylinder walls can lead to reduced compression, increased oil burning, and fuel dilution of your engine's motor oil.

2. Damage to the Piston and Piston Rings—Debris can embed in the piston and rings, leading to poor sealing and blow-by, which results in reduced power.

3. Valve Damage—Debris trapped between the valve and its seat can prevent sealing and damage the valves.

4. Spark Plug Contamination—Debris caught between a spark plug's electrodes can foul the electrodes, resulting in the engine misfiring.

5. Knocking or Pinging—Debris can interfere with combustion, resulting in preignition events.

Worst of all, Debris in the cylinder can lead to catastrophic engine damage, including cracking a piston, damaging a cylinder head, and/or bending a connecting rod.

In other words, Debris in a cylinder can easily result in engine replacement.

How Debris Gets into an Engine's Cylinder(s)

Typically, when foreign Debris gets into an engine, it is because of road and engine dirt that has accumulated around the spark plugs and falls into a cylinder as a loosened spark plug is withdrawn. This is why you should always blow compressed air around the spark plugs and the top of an engine as the first step before removing the spark plugs.

However, there is another potential scenario: One in which the body of the spark plug made of a heat-resistant ceramic material breaks from age and/or improper sparkplug removal technique (e.g., using the wrong type of socket and/or applying some sideways forces against the insulator) and bits of the insulator fall into the cylinder through the sparkplug hole.

Which according to a recent Reddit r/MechanicAdvice topic is an example of what happened to one car owner as he attempted to DIY his vehicle's spark plugs:

Bad Advice Given About How to Handle Debris Falling into an Engine Cylinder

While some of the comments tried to reassure the original post author that since the engine did not appear to go into catastrophic damage mode and appears to be running okay with the hope that the spark plug insulator bits were blown out of through the exhaust valves, several other comments were not just unhelpful…but actually wrong.

Wrong in the sense that the suggestions of:

1. Allowing the bits to blow out through the open spark plug hole while turning over the engine.
2. Applying compressed air into the spark plug hole to force the Debris out.
3. Squirting WD-40 into the cylinder to presumably trap the bits to make removal of the Debris more certain.
4. Pouring motor oil into the cylinder followed by vacuuming it out multiple times to increase the chances Debris is removed.

…were not a guarantee of avoiding making a bad problem worse for the car owner.

Related article: Horrible TikTok Car Advice and a Few Winners

In other words, for lack of a gentler way of saying this, "It is a redneck repair," and prone to lead to more problems when there is only one really correct way to approach the problem—removing the cylinder head to clean out the cylinder and ensure no debris is present before starting an engine.

Yes, removing the cylinder head will take time, energy, and some expense, but it is much cheaper than replacing a ruined engine that could have been avoided.

While I can understand the temptation to take the easy way out with a questionable repair, the forum thread is a good lesson to less-experienced mechanics—take online forum advice with a grain of salt and always follow up by going to a professional mechanic before doing anything else.

Only by digging through the thread comments did I find one where someone described having a similar problem and did the correct repair by towing the vehicle to a garage for cylinder head removal and cylinder cleaning BEFORE even thinking about starting the engine.

An Update to the Owner's Car

According to the owner a few days after the original post and thread comments:

"Update on the situation, I took it to the shop and had them test the engine. It turns out that there is damage done on the cylinder but it's not too harsh. The cylinder wall has some scoring. There's no ceramic leftover but the fuel is mixing with oil in the cylinder. They told me hopefully I can still push out several miles on it before codes are thrown but at this point, it's driving the car with a compromised cylinder."

In short, his car's life is significantly shortened. While it is possible that the engine cylinder wall scoring could have occurred earlier from a different event, the message remains the same:

Should you ever accidentally drop anything into an engine that is not easily removable, you will have to have some disassembly work done on the engine to make the correct and effective repair to avoid making a bad situation worse.

Shortcuts ruin engines. Nuff said.

For additional articles related to questionable repairs, check out these recommended articles:

1. I Think My Mechanic Destroyed My Car –Ford Owner Catches a Bad Fix on Video
2. TikTok Car Repair Hacks You Should and Should Not Do
3. The Worst DIY Repairs…Ever!

Timothy Boyer is an automotive reporter based in Cincinnati who currently researches and works on restoring older vehicles with engine modifications for improved performance. He also reports on modern cars (including EVs) with a focus on DIY mechanics, buying and using tools, and other related topical automotive repair news. Follow Tim on Twitter at @TimBoyerWrites as well as on Facebook and his automotive blog "Zen and the Art of DIY Car Repair" for useful daily news and topics related to new and used cars and trucks.

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