Re: Spica head-to-manifold studs

[Dana Loomis <dloomis@domain.elided>]

As usual, John Hertzman's response in AD V8 #165 to Bruce Giller's question
about intake and exhuast manifold studs on the 105 2000 engine was thorough
and informative.  I haven't researched this question through the parts
books, but would add a couple of observations based on experience with the
cars.    

John wrote "...there is nothing peculiar about 8 x 1 x 8 x 1.25 mm thread 
combinations on Alfa studs; they are ubiquitous.The 1.25 mm coarse thread 
(ISO, JIS, and DIN Standard) is the normally fixed end in the usually alloy 
part and the 1 mm fine thread (DIN Fine) takes the normally removable part, 
a.k.a. 'the nut'. There are very few 8 x 1.25 mm nuts on an Alfa or in an Alfa 
parts-pile - at my last count about a dozen, with four different part numbers, 
on a 2000."    

In my experience, the external engine fasteners are about the only ones on
the car with a fine thread pitch; 8x1.0 is most common, but the 6 mm studs
on the water pump and other assemblies also have fine threads.   Elsewhere
on the car, however, most nuts, bolts and studs use standard metric
threads--1.25 thread pitch for 8 mm fasteners.  This size is readily
available from hardware stores and import-oriented parts vendors.

John went on to say "The studs for the carbureted intake manifold all take the 
same 8 x 1 mm nut (2120.15029) but the studs for the Spica intake manifold 
take two different 8 x 1 mm nuts- five the same 2120.15029 as the Eurocar, but 
two with a different part number, 2120.15053. Please don't ask me why. That is 
one of those little Alfa quirks I would like to figure out someday."

On the SPICA intake manifold, the injectors and fuel lines for cylinders 2
and 3 are very close to the inner two nuts on upper side.  I believe the
original manifold nuts in this location had a thinner  profile than the
others, presumably to either prevent inteference between the nut and the
injector or to make removal possible with the injectors in place.  

I admire John's philosophical position that using fasteners in the
originally-specified sizes can be considered part of the discipline of
preserving the cars and their unique qualities, and generally try to put it
into practice when working on street cars.  At the same time, I know of a
number of substitutions that can be made to work in a pinch, or on a race
car where a certain degree of modification is to be expected.  

Bruce should be able to buy new manifold studs for his engine (I purchased
a set of new ones earlier this year), but if  he couldn't find them, I
can't think of any practical reason why substituting 8x1.25 studs in
approximately the right lengths would not work.

Dana Loomis

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