> I purchased a 5/8 heater nipple from
> CarQuest that had a 1/2"NPT fitting...
We must be talking about different holes. This one's almost 1/8 NPT, but the
same theory should apply.

By the way - I discovered an "interesting" failure mode yesterday....

I took her out for her first taxi test. First impression was that the engine
was running MUCH smoother with the prop in place. Still rich, but much more
responsive. There was a metallic noise I hadn't heard before, so I swung her
around and taxied straight back. As I shut her down I noticed a prop
vibration that didnt seem right.

There was a LOT of lag on the prop. Buly peered down into the flywheel area
and spotted a bolt lying at the bottom of the case, just waiting for the
best opportunity to jump up and attack the expensive and really important
piece of wood right behind the redrive. :(

Wiggling the prop a bit more I noticed that the flywheel was moving a little
with respect to  the counterweights behind it. I removed the redrive. The
entire damper plate / flywheel assembly was loose. I removed the damper
plate and found, behind it, the 6 small bolts and one very large central
bolt that hold the flywheel in place were all loose. I said 6. Actually
there were 5. The other one, the one Buly found, had already come out. This
situation could have taken a very serious bite out of my ass if the
remaining bolts had come out during the first flight. Can you say
"catastrophic failure"?

I know what happened. Three years ago, when we were making the engine mount,
we had assembled  the redrive to the engine. We'd mounted the flywheel and
damper plate, probably finger tight,  at that time. For three years the
engine had sat around with that damper plate in place hiding the loose
bolts. When it finally came time to install the redrive properly I had
forgotten that the flywheel had never been torqued down. It had been "part
of the engine" for all that time, and I'd ASSumed that it had been correctly
installed when the engine was built. I guess this is why we do taxi testing.

Today I'll pick up a new bolt from NAPA and a new bottle of locktite.