Hi John,
You're probably going to hear this from a few people, but the correct OEM
sender has straight, 5/8-18 threads, and the original Tiger F4B manifolds
(or the temperature sender block for the OEM 2 barrel setup) had
corresponding straight threads. The tapered threads you're describing are
3/8" pipe thread, which is close to 5/8-18 in both pitch and diameter, so
that things can sort of go together, but without actually sealing.
Your options are:
1. Find a 3/8" pipe thread sender with the same electrical specs as the one
you just got from SS. Dunno how hard that is.
2. Get a 3/8" pipe tap and a 5/8"-18 straight tap. Use the pipe thread tap
to clean the threads really well on the intake manifold, then plug the
bottom and fill the hole with metal-filled epoxy. Redrill the hole (37/64ths
IIRC) and thread it with the 5/8"-18 tap. This may still not work correctly
if the sender's threads don't reach the metal part of the manifold and
therefore the sender doesn't make electrical contact - it needs to be
grounded. It may also leak if you don't get the top surface of the epoxy
flat enough.
3. Get the hole cleaned, welded, and re-machined by a shop that's
experienced with aluminum manifold repair.
4. Get a 1/2" pipe thread to 5/8" straight adapter (they're specifically
designed for temp sender installation) and, after verifying that the sender
reaches THROUGH the bottom of the adapter, redrill and thread the intake
manifold to 1/2" pipe. Install the adapter with some liquid Teflon sealant,
use the sealing washer on the sender, and it should be all good.
These options are not listed in any order of preferability or cost. "The
Right Thing" would be #3, but it's likely to be the most expensive by an
order of magnitude.
Good luck,
Theo
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