Hi all.  While removing the oil pan on my transmission to reseal I ended up snapping a bolt.  I drilled it out but for some reason I cannot tap the hole.  I'm using a new tap so its sharp but it won't cut any threads.

Any ideas on what I can do?  Thanks

Looks like you drilled it out too big to make threads.

Might need to helicoil that

m6 X1.00 threads

I've not used helicoil before.  How does the insert anchor itself into the hole if there aren't threads?

it just sits in there spring loaded.  the tension is enough to keep it from backing out.  these aren't high torque bolts so that should be good enough

Edited March 11, 20197 yr by nvu

Got it.  I just hope I can find a coil big enough for the hole. 

2 hours ago, palfer said:

I've not used helicoil before.  How does the insert anchor itself into the hole if there aren't threads?

Just to clarify, a helicoil is a coil of square wire.  You oversize drill and tap the damaged hole, then screw the helicoil into the new threads - that's what keeps it in place.  Then the inside of the coil is the new thread your fastener screws into.

 

That was my impression which is sort of the struggle because I can't tap the hole.  Seems the metal is so soft the hole just widens on me.  If I could tap it, I'd just drill out the hole in the pan and use a larger bolt.  Maybe I can get the coil to bite just enough to thread a bolt.  As mentioned, there is very little torque on these bolts, just need it flush to prevent a fluid leak

It's just an aluminum casting - shouldn't be that hard to tap - but you're going to have to use a bottom tap, otherwise a through-hole tap taper is probably going to just chew up the hole.

 

Good to know.  my taps are all tapered at the end and that is exactly what is happening..  Wasn't aware there were variations.

The bottom tap has no taper so it cuts right away?

A very slight taper right at the tip (which is flat so it can tap all the way to the bottom of the hole, unlike the usual pointy tapered taps) just to get it started.