Wir schmieren die Fahrradkette mit Kettenöl.

Because schmieren is the infinitive, and with wir in the present tense, regular verbs usually keep the -en ending:

• ich schmiere
• du schmierst
• er/sie/es schmiert
• wir schmieren
• ihr schmiert
• sie/Sie schmieren

So wir schmieren is the correct present-tense form.

In this sentence, schmieren means something like to grease, to lubricate, or to apply oil/grease to.

Depending on context, schmieren can also mean things like:

• to smear
• to spread
• sometimes even informal meanings in other contexts

But with die Fahrradkette and mit Kettenöl, the meaning is clearly to lubricate the bicycle chain.

Die Fahrradkette is the direct object — it is the thing being lubricated.

The verb schmieren here acts on something, so that thing goes in the accusative case.
The noun die Fahrradkette is feminine singular, and for feminine nouns the article is:

• nominative: die
• accusative: die

So the form stays die Fahrradkette.

You usually have to learn the gender with the noun:

• die Kette = the chain

Since Fahrradkette is a compound noun, the gender comes from the last part of the compound:

• das Fahrrad = bicycle
• die Kette = chain
• die Fahrradkette = bicycle chain

In German compounds, the final element determines the gender.

After mit, German uses the dative case, but here there is no article because Kettenöl is being used in a general, uncountable sense — like with chain oil.

That is very common with materials and substances:

• mit Wasser
• mit Öl
• mit Butter
• mit Kettenöl

If you mean a specific oil, you could use an article:

• mit dem Kettenöl = with the chain oil

That would suggest a particular oil already known in the conversation.

Yes. Mit is a dative preposition.

So whatever follows mit must be in the dative:

• mit dem Fahrrad
• mit der Kette
• mit einem Tuch
• mit Kettenöl

In this sentence, Kettenöl has no article, so you do not see a special dative ending on the noun itself. But grammatically it is still governed by mit.

Because Kettenöl is being treated as an uncountable substance, in a general sense.

Compare:

• Wir schmieren die Fahrradkette mit Kettenöl.
  = We lubricate the bicycle chain with chain oil.
  (general substance)

• Wir schmieren die Fahrradkette mit dem Kettenöl aus der Garage.
  = We lubricate the bicycle chain with the chain oil from the garage.
  (specific oil)

German often omits the article with substances when speaking generally.

It is a compound noun:

• die Kette = chain
• das Öl = oil
• das Kettenöl = chain oil

The -n- in the middle is a linking element often seen in compounds. You do not always need to overanalyze it at first — it is best to learn the compound as a whole.

Also notice that the gender comes from the last word:

• das Öl → das Kettenöl

It is another compound noun:

• das Fahrrad = bicycle
• die Kette = chain
• die Fahrradkette = bicycle chain

Again, the final part determines the gender:

• die Kette → die Fahrradkette

This is very common in German, so getting comfortable with compounds is important.

In a normal German main clause, the conjugated verb usually comes in second position.

Here the sentence starts with the subject:

• Wir = position 1
• schmieren = position 2

Then the rest follows:

• die Fahrradkette
• mit Kettenöl

This is standard German word order for a simple statement.

Yes. That is very natural too.

• ölen = to oil
• schmieren = to grease/lubricate/apply oil or grease to

Both can work, though the nuance may differ slightly depending on context.
Ölen is more specifically to oil, while schmieren is a bit broader.

German often puts extra information like manner, means, or instrument after the direct object.

So this order is very natural:

• Wir schmieren die Fahrradkette mit Kettenöl.

The direct object comes first, then the phrase explaining with what.

You might hear other word orders in special contexts, but this is the most neutral one.

Yes. German present tense often covers both ideas.

So Wir schmieren die Fahrradkette mit Kettenöl can mean:

• We lubricate the bicycle chain
• We are lubricating the bicycle chain

The exact meaning depends on context. German does not usually need a separate progressive form like English are lubricating.

You would use sie, because die Fahrradkette is feminine:

• Wir schmieren sie mit Kettenöl.

That means We lubricate it with chain oil.

Be careful: sie can also mean she or they, so context matters.

No, schmieren by itself is not separable.

So you simply say:

• Wir schmieren die Fahrradkette.

But there are related verbs with prefixes that may behave differently, for example:

• einschmieren can be separable in many uses

For this sentence, though, plain schmieren is just an ordinary verb.

The plural is die Fahrradketten.

So:

• singular: die Fahrradkette
• plural: die Fahrradketten

Example:

• Wir schmieren die Fahrradketten mit Kettenöl.
  = We lubricate the bicycle chains with chain oil.