who is right?

[Sunny43.5]

If you can prove it then HELL yes go back .

[jets]

Big black smoke occurs when having to accelarate heavily.

That is fairly normal, mine does the same & my timing is spot on.Try to avoid doing that as well as using more fuel it clogs up the EGR valve & inlet manifold.

[jets]

it seems the mechanic who did the belts forgot to tighten a bolt which caused the issue at hand.

I have posted on another forum how important it is that belts change requires careful work with the correct information & tools.
I am not saying that this has occurred in your case but many owners just shop on price when they should be shopping for the best careful mechanic who has done this job many times before with 100% success.
There has been a owner selling parts from his van on Ebay where a belt change went wrong & the resulting damage caused him to write the van off.

[Gigitt]

After TB change you still have to check and adjust the VE Injector Pump timing. TB alignment does get you in the ball park so the engine will run. But there is a procedure where you loosen the IP and rotate it ever so slightly alters the timing back to be on spec. You do need VCDS or shop software to check IP timing. As you belt ages it can stretch enough to retard the IP timing again, and so you just adjust the IP again.
I just had the same problem with my Mk3 golf TDI smokey as hell and IP timing off the chart. Reset it and now purring like a Tracktor

[gfh]

Thanks for the input guys.But there is more! After all that work I hear more engine noise the other day. Now it seems that the acoustic balancer needs replacing,also it was found that the belt had turned over itself because it was not tensioned properly by the first mechanic who now no longer works with this firm! Refund likely?

[jets]

What you call the acoustic balancer is normally called harmonic balancer & I can't see that being affected by the first mechanic unless it was mechanically damaged. These things have a limited life, maybe 200,000km & fail when the rubber part starts cracking. You need more info from the second mechanic as to why it needs replacing. Maybe he is saying it needed replacing by the first mechanic & he didn't check it.
As far as looking for a refund I would have thought the firm would still be responsible even if the mechanic who did the work has moved on.
That is only my opinion though as I do all my own work & don't get involved in that stuff.

[brad]

Generally speaking, if you get workshop A to do work & then get workshop B to do more work without allowing workshop A to make good then you are out of luck as it becomes a "he said / she said" situation.

Unless of course workshop B is willing to provide documentation proving workshop A was somehow responsible for the problem (good luck with that).

Any warrantable items are connected with the business & not the mechanics that work for the business, so even if staff come & go, the business provides the warranty on workmanship & parts.

[gfh]

The balancer was cracked as shown to me by mechanic 2. But the worst thing discovered was the replacement parts renewed by mechanic 1 failed. Of course he is using the if you came back to us first................... Was told by mechanic 2 that I was extremely lucky not to have dropped a valve. Mechanic 1? would have thought he had a moral obligation........yea I know dreamin.