"by" as adverb

[notmyname216]

Given this sentence:

The ball was kicked by Jim.

I read that "by" is NOT a preposition in this sentence. Instead it is a adverb.
Is this because it is a passive sentence?

If the sentence was this:

Jim kicked the ball by the car.

Is "by" a preposition because the sentence is a active sentence?

Is a sentence always passive by the existance of a auxiliary verb?

[JJM Ballantyne]

I'm not sure where you read "by" was an adverb.

It's a preposition.

[notmyname216]

Here is the link were it says it is a adverb and explains why it is:

http://www.csun.edu/~galasso/completehandbook4.htm