Hi all. Tom Walter's recent post on threads has inspired me to
"republish" my original article that I wrote for the Roadster Review
in 1992, and was later slightly revised and republished in the
MADROC review in 1996. I have revised it again, adding some info on
SU's. In this article, Solex = Mikuni, and SU = Hitachi.
Some of the data is in chart form, and you may need to reformat the
message to an old style non-proportional font such as "Courier" to
view it correctly. In addition, if anyone wishes to post this on
their website, they are free to do so, provided it is NOT copyrighted.
ROADSTER THREADS (revision #2)
Note: my knowledge of Datsun Roadsters is limited to 2000's (mostly
early Solex models), so there may other threads involved on 1500's and
1600's, as well as on 2000 SU's, or very late model 2000's.
Roadsters were originally based on British sportscars, so they used inch
size threads, including British (not American) pipe threads. With the
introduction of the 2000, in the middle of 1967, Nissan started to use
metric threads. The engine and transmission were supposedly totally
metric, and the chassis remained inch sizes.
There were exceptions in the "all metric" engine/tranny:
* the pipe threads remained British
* the rod bolts were 7/16-20 UNF
* the head bolts were an odd combination of 7/16-14 UNC threads
with a 10mm socket head
* there were two 5/16-24 NF nuts and bolts between the engine plate
and the tranny (at the bottom)
* the clutch slave cylinder still used 3/8-24 threads for the hyd-
raulic line, although the push rod and mounting bolts were metric
And, on top of that, metrics weren't quite as standardized in 1967 as
they are today. There was in process an ISO (for International
Standards Organization) standard, but a lot of what Nissan used didn't
meet those standards, at least at first. Some of the original threads
on small screws in the alternators, distributors, and Solexes were
French metric standard (coarser than ISO), and many of these were
changed to ISO before the Roadsters went out of production. Also, the
head (hex) sizes of most nuts and bolts were smaller than ISO, and
these never changed. I learned in 1996 that Japan has its own metric
thread specification, which I think is JIS; I haven't seen a copy of
it, but I can speculate that it calls for the smaller hex head sizes.
I believe Toyota, and also Porsche and Mercedes-Benz, and some motor-
cycles use these smaller hex sizes, at least sometimes.
My knowledge of SU's is limited, but I played with some a few years
ago, and found some with 10-32 NF threads, as well as some with
5x0.8mm ISO threads, as well as some with (I think) 5x0.75 FINE
metric threads!!! Never came across any of the coarse French pitch
threads on SU's, just on Solexes (doesn't mean that there weren't
any though)
How do you check a thread? The best way is to check it with a thread
gage; this is a bit like a set of feeler gages, except each has a
series of notches (teeth) along one side which correspond to a
certain pitch. It either fits perfectly, or it rocks; also, hold
it up to the light. You should also check the diameter with a
micrometer (or caliper) or with drill gage. And finally, you should
check it with a known mating bolt or nut. If you don't have a mating
nut, one bolt can be checked against another; again, they either fit
perfectly or rock. While even the difference between a 0.70mm
(.0276") and a 0.75mm (.0295") pitch isn't too tough to spot, certain
combinations of inch and metric are awfully close together, in pitch,
diameter, or both. A particular example (Datsun uses both): 10-32 NF
(.03125" pitch/.190" dia) versus 5x0.8mm (.03150" pitch/.1968" dia).
Fortunately, the slight diameter difference gives it away, a 10-32
screw being very loose in a 5x0.8 nut, whereas a 5x0.8 screw won't go
into a 10-32 nut. Be careful! (it "burned" me once, long, long ago!)
METRIC NUTS AND BOLTS [HEAD/WRENCH SIZES GIVEN IN BRACKETS]
Datsun ISO (reference only)
6x1.00 [10] 6x1.00 [10]
8x1.25 [12] 8x1.25 [13]
10x1.25 [14]
10x1.50 [14] 10x1.50 [17]
12x1.75 [17] 12x1.75 [19]
* Sears has a huge selection of individual metric taps and
dies in the catalog, including the odd coarse pitch ones,
or you can try an industrial tool or metric supply house
* Datsun uses both 10mm pitches shown; protruding studs or
bolts, plus nuts are the fine thread; threads into engine
or tranny parts are coarse
METRIC SCREWS (AND NUTS)
early late early late
alt/dist alt/dist Solex Solex
4x0.75 4x0.70 (ISO) 4x0.75 4x0.70 (ISO)
5x0.90 5x0.80 (ISO) 5x0.90 5x0.80 (ISO)
6x1.00 (ISO) 6x1.00 (ISO)
8x1.00 8x1.00
PIPE THREADS ["gage" dia for BSPT, pipe dia for NPT in brkts]
British (Datsun) American (reference only)
1/8-28 BSPT [.383"] 1/8-27 NPT [.405"]
1/4-19 BSPT [.518"] 1/4-18 NPT [.540"]
3/8-19 BSPT [.656"] 3/8-18 NPT [.675"]
1/2-14 BSPT [.825"] 1/2-14 NPT [.840"]
* although British and American pipe threads both have 3/4
inch per foot taper, and their diameters are very close, the
included angle of the threads themselves, or "Vee", is 60
deg for the American pipe threads (same as for UNF, UNC and
metric threads), but only 55 deg for British (same as for
British Whitworth threads; thanks to Stan Chernoff for this
tidbit); therefore don't think you can replace the 1/2"
drainplugs on the tranny and rearend with American ones,
unless you retap lightly, with the NPT tap
* Sears has the 1/8" and 1/4" British pipe taps and dies
in the catalog; larger ones can be obtained from industrial
tool and metric supply houses, but make sure you get BSPT
(tapered) and not BSP (similar size, but straight)
CORRECT 2000 TIMING CHAIN COVER BOLT LENGTHS (mm)
view of engine non-smog smog equipped
A F A 90 F STUD A 90 F STUD
B G B 98 G STUD B 85? G STUD
C H C 98 H 40 C 85? H 40
D I D 65 I 70 D 65 I 72?
E J E 65 J 70 E 65 J 72?
* bolt hole(s) "H", and sometimes "I", need(s) to
be sealed inside the block to prevent oil weepage
* stud in "F" can be replaced by 8x1.25x90mm bolt
MISCELLANEOUS
-brake lines: 3/8-24 inverted flare
-grease fittings: 1/4-28
-oil drain plug: 3/8-19 BSP [not BSPT]
(i.e., straight British pipe thread)
-water temperature sender: 5/8-18 UNF
-oil line to distributor: 10x1.00 flare plus 10x1.00 inverted
flare (metric); (this is for most 2000's; my recollection is
that very late 2000's had a different distributor support and
hose, and that I've seen two other style distributor supports,
but they were probably from a 1600)
----------original message----------
Date: Sun, 26 Aug 2001 15:47:11 -0500
From: Thomas Walter <twalter@austin.rr.com>
Subject: Re: There's a screw loose in the garage
Linda,
What year roadster?
The '63-67 model are all SAE FINE THREAD (USA thread)
The '67.5 models are UNIQUE METRIC when it comes to small
4mm and 5mm screws on the carbs & alternators. From what
I have learned Hitachi used a FRENCH standard for those
small screw threads. Near impossible to find now (yes,
I even looked in France - it seems not ALL french OEMs
used the same metric threading standard).
The '68-'70 models are ISO Metric. On the small screws there
is a small dimple on the screw head to note "ISO" (International
Standards Organization. Those screws are much easier to find.
Odd thing about odd threads, most of the US standards really didn't
come into play until WW2. Up until that time every company used
their own threading standards. It was the AN (Army Navy) that started
to realize that was insane, as a 1/4" bolt could have something like
14 different threading to it!!! So they put their foot down, and
starting specifying you could basically use only one of THREE different
threads... which later went to "fine or course" thread. So a 1/4" bolt
would either have 20 tpi threading or 28 tpi threading. Made life much
easier for those service folks to keep everything going on the field.
Meanwhile, the ISO standards could never really agree on things.
So the German ISO group liked 13mm and 15mm bolt heads on 8 & 10 mm
bolts. While in Japan, they felt the 12 and 14mm bolt heads were
better suited for their use.
Threading standards are like the old joke of a perfect world:
English are the police, Germans the mechanics, and French the
cooks. In reality we get German police, French mechanics, and
English cooks!
Cheers,
Tom Walter
Austin, TX
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