The spark plugs should be the same height, assuming that all the plugs are of the same manufacturer.
If one plug appears different it may be due to having a 'different' plug fitted. There's long-reach and short-reach spark plugs. It's the length of the threaded portion that differs.
It may also be due to an incorrectly fitted plug. This happens when somebody screws a plug in and it isn't straight in the threads and becomes 'cross threaded'. It won't ***** fully down because it has become cross threaded and is tight/seized.
Trying to ***** the plug further in will cause damage to the thread in the head - as will trying to remove it. Any damage to the threads in the spark plug recess can mean that a helicoil thread is needed - and it isn't a cheap job.
My advice is that unless you know what you're doing is NOT to try to ***** or unscrew the plug. Your car is running - take it to a workshop/mobile mechanic and ask their advice. They will probably be able to remove the plug and refit/replace it without causing any damage.
Answers & Comments
The spark plugs should be the same height, assuming that all the plugs are of the same manufacturer.
If one plug appears different it may be due to having a 'different' plug fitted. There's long-reach and short-reach spark plugs. It's the length of the threaded portion that differs.
It may also be due to an incorrectly fitted plug. This happens when somebody screws a plug in and it isn't straight in the threads and becomes 'cross threaded'. It won't ***** fully down because it has become cross threaded and is tight/seized.
Trying to ***** the plug further in will cause damage to the thread in the head - as will trying to remove it. Any damage to the threads in the spark plug recess can mean that a helicoil thread is needed - and it isn't a cheap job.
My advice is that unless you know what you're doing is NOT to try to ***** or unscrew the plug. Your car is running - take it to a workshop/mobile mechanic and ask their advice. They will probably be able to remove the plug and refit/replace it without causing any damage.