Assim que terminar, guardo a bomba de bicicleta.

Here, terminar is functioning as the future subjunctive, not as a plain infinitive.

After expressions like assim que, Portuguese normally uses the future subjunctive when talking about a future event:

Assim que terminar = as soon as I finish / as soon as he finishes / as soon as you finish

With many regular verbs, the future subjunctive form for eu/ele/ela/você looks exactly the same as the infinitive, so it can be confusing.

Yes, absolutely. Assim que eu terminar is correct.

In Portuguese, subject pronouns are often omitted because the verb form and context usually make the subject clear. So Assim que terminar is the more natural, compact version unless you want emphasis, contrast, or extra clarity.

Portuguese often uses the present indicative to talk about the future when the timing is already clear from the context.

So guardo here means something like I put it away / I’ll put it away. Because assim que terminar already points to a future moment, the future meaning is understood.

You could also say guardarei, but that sounds a bit more explicit or formal: Assim que terminar, guardarei a bomba de bicicleta.

Because Portuguese commonly drops subject pronouns when they are not needed.

The verb guardo already tells you the subject is eu, so saying eu guardo is only necessary for emphasis or contrast.

This is very normal in European Portuguese.

Not by itself. Terminar in this form could refer to I, he, she, or you depending on context, because those forms can look the same here.

In this sentence, most people will understand it as I finish, because the main verb guardo clearly has eu as its subject, and the listener usually assumes the same subject unless something else is stated.

If you wanted a different subject, you would normally make it explicit: Assim que ele terminar, guardo a bomba de bicicleta.

Here guardar means to put away, to store, or to keep.

This is a useful word because it is often a false friend for English speakers. It does not only mean to guard in the sense of protecting something. In everyday Portuguese, guardar very often means put away or keep.

So in this sentence, the idea is that the speaker will put the bicycle pump back in its place.

The article a means the.

Portuguese uses articles more regularly than English, so where English might sometimes leave them out, Portuguese usually keeps them. Here a bomba de bicicleta means the bicycle pump, referring to a specific pump that both speaker and listener can identify from the situation.

If it were not a specific one, you could say uma bomba de bicicleta = a bicycle pump.

Bomba de bicicleta is the normal way to say bicycle pump. Here de bicicleta describes the type or purpose of the object.

So it means: a pump for bicycles / a bicycle pump

If you said bomba da bicicleta, that would more naturally mean the pump of the bicycle or the bicycle’s pump, which sounds more like possession and is less neutral here.

Because Assim que terminar is a subordinate time clause placed before the main clause.

In Portuguese, when this kind of clause comes first, it is normally separated with a comma: Assim que terminar, guardo a bomba de bicicleta.

If the order is reversed, the comma is often omitted: Guardo a bomba de bicicleta assim que terminar.

Yes.

Quando terminar means when I finish and is a bit more neutral.

Logo que terminar is very close to assim que terminar and also means as soon as I finish.

So the difference is mostly one of nuance: assim que = immediate, as soon as quando = simply when logo que = also as soon as, quite close in meaning to assim que