If you ever strip a bolt hole, keep the following things in mind:
1. When you buy a tap, buy the bolt at the same time.
2. Get the right size tap wrench.
3. Make sure you have *both* sizes of drill bits necessary for tapping
a larger hole.
4. Make *doubly* sure your drill can *use* the bits you have (cutoffs
are usually 1/4" and 3/8")
5. Be careful with the tap. Use lots of cutting oil.
6. THE BOLT MUST HAVE THE SAME THREAD SIZE AS THE TAP!
My story (short version [hah]):
In fixing my TR7, I managed to strip the thermostat housing bolt-hole,
in the aluminum (sigh) intake manifold. Fine, I borrowed a car, and
bought a tap, a bolt, a washer, and a tap wrench. Went to my uncle's
house and used his vice and drill to bore out the housing cover. Found
out he didn't have the other size bit (basis for the other hole).
Borrowed drill and long extension cord.
Went back to hardware store and got bit. Went home, found out bit
didn't fit in drill, and tap didn't fit in tap wrench. Hardware store
had the larger wrench; friend had a larger drill.
Drilled and tapped hole. Put housing on, bolted down, and the bolt
stripped the hole, for lack of "meat". "Hmm," I thought, "I can
probably just get away with taking the washer out." Sure enough, it
holds (barely).
That was two days ago. Today, I overheated again. Found the water had
gotten out through a leaky (ta da!) thermostat gasket/housing. Removed
cover, and some aluminum bits came off on the bolt (uh oh). Even with
a longer bolt and deeper tapping, the 3/8" hole is a goner.
Bought larger tap, larger bolt, and larger drill bit. Found my uncle's
*good* drill was also only 1/4". Ended up using the 1/2" drill
attachment on his radial arm saw. Bored out larger cover hole, drilled
out housing hole, and started tapping, *carefully*.
"Uh oh. The bolt doesn't go in very far. Wait a minute..." found
bolt was different thread from tap. Go back to hardware store. The
only 7/16" bolts they have are SAE, not USS (tap was 14 tpi USS).
Somehow, I get lucky and find the only 14 tpi 7/16" bolt in the store
that's less than 3 feet long. Even though it's 1 1/4" too long, I
buy it, along with enough stuff to space it out correctly.
Finally, everything's fine. Well, in the thermostat, anyway.
--
Donald Tsang "Ho! Haha! Guard! Turn! Parry! Dodge!
tsang@june.cs.washington.edu Spin! Ha! Thrust!"
...!uw-beaver!june!tsang -- Robin Hood Daffy
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