nutty pedantry (was: 2000 crank pulley nut size)

["John Hertzman" <johnhertzman@domain.elided>]

Joe Fillip asked "Can anyone tell me the size of the crank pulley nut on an
Alfa 2 liter (in my case, a '78 Sports Sedan)? I seem to recall that it's 37
mm, but I'm not certain. Also, is there an SAE equivalent for the metric
socket for this nut?"

Andrew Watry replied "it's 38mm, at least it is on my early 70s 2000s. I
couldn't find that size metric socket, but 1 1/2" is what I could find that
worked.  If you could find it, I think 1 7/16" might be even better, if not
too tight."

John Fielding added "both my Alfa motors (2L & 1.8L) have a 36mm crank nut.
Is the 38mm nut something peculiar to NA Alfa's ??"

The Euro "Tutte le versione" 105 Catalogo Rapido of 1974 lists for all models
a crank nut of conventional configuration #105.00.02.105.00, the first 105.00
part indicating it was there from the first 105s. The USA Alfetta Catalog
Rapido and USA main Alfetta parts book both list 105.50.02.105.00, shown as a
conventional open nut in the illustration in the Catalogo Rapido but shown as
a closed-end capnut with a cylindrical sleeve through the crank-pulley bore in
the main USA Alfetta parts book. This part number is beyond my source-tracing;
there was no 105.50 car type produced, and my understanding is that these
untraceable numbers originated in engineering projects which did not bear the
same number in a production version. It implicitly preceded the Alfetta, as it
would otherwise have had a 116 part number.

The only engines which I have out of cars at this house are an Alfetta engine
with a closed-end cranknut which is a slightly sloppy fit for a 1.5" Sears
12-point socket, and a 1973 Euro two-liter with an open-end cranknut which is
a very snug fit in a six-point factory tool (A.5.0126) which does not have a
marked size but seems to be 36 mm. That nut is a very sloppy fit in the 1.5"
socket, which may be why Andrew thinks "1 7/16" might be even better"

For inch-wrench approximations 38 mm is about 1.49606", while 36 mm is about
1.41732",  well under the 1.4375" of a 1-7/16" socket, which is probably why I
sprung for the factory tool. Sear currently catalogs a 36 mm 12-point socket
for $6.99 (but no 38 mm) and an inch-and-a-half twelve point for $5.49 (but no
1-7/16"). Snap-On doesn't seem to list anything over 32 mm in standard-duty
sockets but does go up to 36 mm in half-inch drive impact sockets and has both
36 mm and 38 mm in three-quarter-inch drive impact sockets, but I didn't price
them.

Your nuts may differ. For inch-metric make-do duty generally, a millimeter is
roughly .03937", and a comprehensive inch-metric wrench approximation chart
isn't too hard to do with a pocket calculator. Back in the fifties Sports Cars
Illustrated published such a chart covering a couple of British systems as
well as metric and inch. Life is easier now, except for some vintage-car
people.

Good luck.

John H.
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