WARNING, another 'story' from Neil......
Barney Gaylord wrote:
>
> At 01:58 PM 9/19/98 -0700, Simon Matthews wrote:
> >Does anyone know the thread used on the bolts that hold the hood frame
> onto the car on an MGA?
>
> In the sides of the body, 1/4-28 UNF or SAE thread. In the top bow for the
> thumb screws, 5/16-22, a very strange thread indeed, no taps or helicoils
> generally available. When I stripped one I tapped it out to 3/8-24 UNF and
> made my own wing bolt.
>
> Barney Gaylord
> 1958 MGA with an attitude
The 'strange' threads will be British Standard Fine, or BSF. This was
used by Nuffield AND Austin on their bodies for some time, up until 1956
on the Morris Minor for instance. From about 1954 to 1956 you can get a
mixture of threads, especially in anchored nuts. Whilst 'free' nuts and
bolts may be UNF, (ANF), those fitted on the press-lines building, the
body panels at Pressed Steel, ( BMC's press shops,) may be BSF. Usually,
( though not always, as anyone with an XPAG engine will tell you...) if
the head is an A/F size it will be the UNF/ANF thread; if it is an odd
size, ( to the USA) it will be BSF. ( Just to really confuse you, BSF
head sizes are actually measured in BSW ( British Standard Whitworth,)
sizes, but one diameter down.....ie 3/8" BSF is a 5/16" BSW spanner)
size.)
NORMALLY, ( if there is such a thing,) UNF heads will also have three
small linked circles stamped into the metal, OR a large embossed ring
round the outer edge of the head ( on the bolt/set screw only,) OR a
small chamfer around the centre of the hexagonal corners, cut about the
centre making the nut look as if it is two locked together.
Nothing like the British to keep things simple...EH. I keep a set of
thread guages handy, simply because of the mixture you can find... BSF,
BSW, BSP, BA, Cycle threads, UNF,( ANF,) UNC, ( ANC,) Old metric, ISO
metric, ect.
Luckily, all BMC 'A' and 'B' series engines use UNF and UNC......well
almost. The modern MG Metro uses these threads with METRIC bolt heads on
its 'A' series, so the mechanics only need one set of spanners at the
garage.
Neil.
( The XPAG/XPEG use ancient French metric threads, with BSW heads, but
that another story. I will bore you to death with that story if you
want, it is quite interesting.)
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