Re: helicoil or similar for blind hole?

Nate Nagel wrote:

I have a thermostatic fan clutch that I'd like to use on my old
Studebaker, but one of the holes where the fan bolts on is stripped. I
am hesitant to drill any farther into the housing to make the repair,
and am wondering how one deals with this situation where one can't run a
tap all the way through. If I were to take a Helicoil tap and cut the
end off to make a bottoming tap would that work? How do you break off
the little tang in this instance? Or is there a better product for what
I'm trying to do? (Timeserts? but where do you actually buy them?
only place I've seen them used is on old Porsches...)

Helicoil taps supplied in kits are all bottoming taps (at least I've
never seen one that wasn't.

The insert manufacturers also supply tang breaking tools but none work
any better than hemostats, which are cheaper as well as being useful
for other things.

The trick is to cut the insert to the correct length before you fit
it. Alternatively you can get a tool for backing them out of a blind
hole (which looks like an arrow head). The open end of the insert
needs to be a quarter of a turn or so below flush when fitted... nor
can you bottom out the tang end as it will cause the threads to bind
when you screw a bolt into it. A helicoil insert is a lot stronger
than the original thread, so you don't need the same depth of thread.

You can also break off the tang with a pin punch if the insert is
fitted correctly (isn't bottomed out) but hemostats are the foolproof
way to do it.

Other thread inserts exist, eg Caterpillar, but the only advantage is
they take a bit less skill to fit. The disadvantages are many.

--
John H
.

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