Re-tapping M8 x 1.25 threads for hot side of Turbo to Downpipe

[Zeille]

Hi all,

I recently swapped a 19k-mile stock turbo from a 2015 fiesta ST into my 2017 Fiesta ST with 178k miles. My buddy and I ran into a few issues doing the job, but one of those namely being:
I bought the new downpipe bolts from the dealer (at $12/bolt). We started to try and thread one in once the turbo was in. It would go in a bit, and then stop. We tried to do it more, and it gave us immense resistance. We then pulled it out, and the threads of the bolt were cooked. We ended up going to Home Depot to get some grade 8 M6 bolts with washers and nuts to mount the downpipe to the turbo (without having to use the threads in the turbo), but it won't hold for super long, as they weren't hardened steel, and the washers started to crush themselves.
I will eventually need to replace them, but I feel I will need to re-tap the threads in the turbo. I purchased a titanium coated tap online, but am curious: if I remove the downpipe but leave the turbo in, would I be able to fit a tap in there to clean the threads/re-tap the threads with the turbocharger still in the car? I would prefer not to remove it, as I'd have to spend plenty of time and money to get new gaskets in order to do that. Is it doable without removal?

 

[Grsemky]

I was curious if you were successful in the swap, sucks about the stud... There should be enough space to get a tap in there with turbo installed. Chasing threads doesn't take a lot of force so if the tap fits you'll be good.

 

[scooter123]

You might be able to get away without snapping the tap but odds are only about 10% for that. If you haven't ever snapped a tap while threading a hole I can tell you that it can be a real horror getting that broken tap out of that hole. On occasion before I retired we had to send out forming dies to have the broken tap removed by dissolving it with Carbon EDM. It can take up to 4 hours of expensive machine time to do this so the cost in 1985 was 120 dollars, with inflation and the loss of machine shops in the US this would probably be 500 dollars a hole today.

I strongly advise you to remove the turbocharger. Because if you snap that tap you will probably have to remove the engine from the car. Note you will need to have that tap as perfectly square to the hole as possible so pay attention to that from the start. I will also warn you that WD-40 IS NOT a suitable lubricant for tapping, instead use Motor Oil or axle grease. Yes you can also purchase Tapping fluid and that is a bit better than motor oil but it's not essential if you are careful. I will also note that at any point where you feel the tap "stall" reverse direction immediately and back the tap out a bit and then resume tapping, When you are hand tapping getting the tap perfectly square is not likely but this back and forth approach will allow the tap to "find" the centerline and once there you won't feel the tap stall until you approach the bottom of the hole. I will also note that there are a lot of chips that accumulate in front of the tap so a bit of mig welding wire with a hook at the end and an air nozzle can make it possible to drag those chips out of the hole and gain another 2 or 3 threads in that hole.