Voisitteko kiristää löysän ruuvin ja tarkistaa ketjun?

It is made of three parts:

• voi- from voida, meaning to be able to / can
• -sitte, the conditional ending for you (plural) or polite you
• -ko, the yes/no question particle

So Voisitteko... ? is literally something like Could you...? It is a very common and polite way to make a request in Finnish.

Finnish often uses 2nd person plural to sound polite or formal when addressing one person, especially in customer-service situations.

So Voisitteko can mean:

• Could you? to one person, politely
• Could you all? to more than one person

In this sentence, it most likely sounds like a polite request to one person, such as a mechanic or shop worker.

Voitteko means can you?, while voisitteko means could you?

The conditional form voisitteko makes the request softer and more polite. English does the same thing:

• Can you tighten... ? = more direct
• Could you tighten... ? = more polite

So this sentence sounds courteous rather than blunt.

-ko / -kö is a question particle used to turn something into a yes/no question.

In this sentence, it is attached to Voisitte to make Voisitteko. Finnish usually attaches this question particle to the first important word in the sentence.

So:

• Voisitte = you could
• Voisitteko? = could you?

After voida (can / could), the next verb usually appears in the first infinitive, which is the dictionary form.

So:

• voisitteko kiristää = could you tighten
• voisitteko tarkistaa = could you check

The sentence has one finite verb, Voisitteko, and then two infinitives joined by ja:

• kiristää
• tarkistaa

This is completely normal Finnish structure.

Because ruuvi is the object of the verb kiristää, and here it is treated as a complete, finished object: the speaker wants the whole screw tightened.

In the singular, that object often takes a form that looks like the genitive:

• ruuvi → ruuvin

The adjective must agree with the noun, so:

• löysä ruuvi = a loose screw / the loose screw
• löysän ruuvin = the loose screw as the object

So both words change:

• löysä → löysän
• ruuvi → ruuvin

For the same reason: ketju is also a complete object here. The speaker wants the whole chain checked.

So Finnish uses the total object form:

• ketju → ketjun

If you said ketjua, that would suggest a partial object, which often gives a sense like:

• checking some of the chain
• checking the chain in an ongoing or less bounded way

In this sentence, ketjun is the natural choice because the request is to check the chain as a whole.

No. Finnish does not have articles like English the and a/an.

So ruuvin and ketjun do not themselves tell you whether English should use the or a. That usually comes from context.

In practice, the sentence could refer to:

• the loose screw
• a loose screw
• the chain
• a chain

The situation tells you which English version sounds right.

It sounds polite and natural, especially in a service situation.

Two things make it polite:

• the conditional form voisitte-
• the plural/polite you

A less formal version to one person would be:

• Voisitko kiristää löysän ruuvin ja tarkistaa ketjun?

A more direct version would be:

• Voitko kiristää löysän ruuvin ja tarkistaa ketjun?

So the original sentence is a good, courteous way to ask for help.

Yes. Ja simply means and.

It connects the two infinitives:

• kiristää = to tighten
• tarkistaa = to check

So the speaker is politely asking for two things in one sentence:

• tighten the loose screw
• check the chain

This is a very normal way to combine requests in Finnish.