It can be, depending on what you get in there. If it is a metal shaving or something hard enough to survive the temperature you could damage a seal, or cause valve damage, but if it is just a piece of lint or dust I wouldn't worry.

When I remove a spark plug is it bad news if dirt or grime falls into the engine
Saw this thread while investigating what sounds like the same problem with my jeep. The check gauge light came on and my battery gauge bottomed out. But  weird thing is, it ran fine. I drove it a few miles home, and turned it off, then started it again and the same thing happened real quick. What should I approach first since it's running ok. I do have some rust damage underneath. This jeep came from Detroit so its been in salt and snow for a long time, I just bought it and this is the first time its done anything weird. I could have a corroded connection or should I go right at Alternator being the culprit.
Thanks in advance for any advice,this is my first Jeep
