spark plug electrode broke off went into cylinder

"Rob



Rep: 1




2


1"

"Hi,

that depends on what happened to the electrode. First scenario would be that it was blown out of the cylinder and is now somewhere in your exhaust pipe. Second scenario would be that the electrode is still somewhere in the cylinder, maybe between the piston and the cylinder, that might lead to scratches and that to severe damage of the engine. Third scenario would be that the electrode stuck between the valve and the valve seat, the piston went up and hit the valve, and now the valve is bent.

The scenarios are sorted from: sounds logic, maybe and ......naaah"

"Still attempting to figure this one out? I think Bosch answered correctly…

Bosch indicates low KV will cause ground electrode damage, aka barely enough spark to fire the plug, additionally they indicate additives can be the cause.

Other manufacturers indicate loose plugs can be the cause due to vibration (NGK), also loose plugs tend to damage plug threads, as the thread is the point of electrical connection and loose plugs would experience intermittent grounding.

Historically its been contributed to tick over or run on from deposits on the top of the pistons, caused from low octane fuel …. but this is an old 1980s problem prior to fuel injection, where carburetors would feed continuous fuel to the engine.

Other proclamations are lean mixture and Rich mixture in the cylinders, however with todays vehicles this is doubtful unless one modified their engine, and fuel system.

Finally there are stories of this condition (missing ground electrode) occurring often with Subaru vehicles. The owners remove all of the plugs, throughly clean the threads and clean out the bores, replace the plugs and plug wires, and the problem goes away. Therefore its highly likely the Bosch answer is correct, as dirty plug threads would cause problems with electrode grounding. This can be exacerbated with the use of anti-seize compound on the spark plug threads, which is a mistake common among mechanics who ignore the fact later plugs have anti-seize nickel applied during manufacturing and therefore need no further anti-seize applied to the threads.

Hope this helps resolve the issue for folks with this predicament"

As someone who has had the unfortunate experience of this happening, you definitely do not want to start the engine. For me, the electrode did not blow out of the exhaust instead it stayed in the piston area damaged the piston, valves and head. Luckily it was not so bad it could not be repaired (the cylinder block did not get scratched) but it definitely caused other problems. I repaired it myself but if you had to take this into a shop it would have been costly. See if someone can scope it and see if the electrode is in there, otherwise the engine head may need taken off to check.