Retapping a hole MK3 Fiesta

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Fri 20 May 2005 21:26
Retapping a hole MK3 Fiesta - Steveo4869
Bit of advise if I may. I need to re-tap a hole which secures the tranmission bearer to the chassis of my Ford fiesta MK3 as I have stripped the tread on 2 of the 4 mounting holes on removal. My question is how easy is it to re tap a hole with a tap and die set and as the original hole carried a bolt with a 17mm head will I have to go the next size up or can I restore the hole to the original size.
Many Thanks
Steveo
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Sat 21 May 2005 17:11
Retapping a hole MK3 Fiesta - Number_Cruncher
Hi Steve,

I suspect that the original bolts were M10, i.e., the diameter measured across the outer tips of the thread is 10mm.

If you have stripped these threads, you can either install a heli-coil thread reair, and use new M10 bolts, or, if there is the required clearance drill out and re-tap for, perhaps, M12. (M11 isn't a preferred size). There may be an imperial size somewhere in between (7/16 BSW or BSF?).

If you choose to go for M12, then the following sizes are applicable;

Tapping drill - 10.2mm diameter
Clearance drill - 12.2 mm diameter

If you fit a hex-head screw or bolt, you will need sufficient clearance for a 19mm hex. You may need to fit a socket head cap screw or bolt instead.

I hope that helps,

number_cruncher
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Tue 31 May 2005 20:27
Retapping a hole MK3 Fiesta - Steveo4869
Many Thanks for the advise I'm only just getting round to sorting it now. I have a 12mm HSS drill bit will this be ok as the clearance drill to retap a M12 bolt hole?
Many Thanks
Steveo
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Tue 31 May 2005 21:10
Retapping a hole MK3 Fiesta - mjm
12mm will be a bit close. A 12mm bolt will be about 11,8 or 11,9mm diameter. You may be lucky, but can you not drill 12mm and use a round file to open the hole up? I am assuming that it is in a bracket, so you only need to open it up enough to get the bolt to fit. If the existing threads are not too bad you may be able to clean them up with either a tap or a bolt with a cut across the end of it.
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