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T100 cylinder base nuts, 17/32" across flats? #615443
09/01/15 3:02 pm
09/01/15 3:02 pm
Joined: Apr 2015
Posts: 514
UK
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Dibnah Offline OP
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Dibnah  Offline OP
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Engine oil leaking out of the base of the barrel on my T100-engined scrambler, having problems finding the right ring spanner (wrench!), 1/2" AF is too small, 9/16" AF is too big. 14mm is slightly too big, are these nuts 17/32" across flats?

There are double ring spanners available in 1/2" and 7/16" AF specifically for the cylinder base nuts on Triumph twin, assume these must be later than 1960?

17/32" across flats must be close to 1/4" Whitworth and 5/16" BSF

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Re: T100 cylinder base nuts, 17/32" across flats? [Re: Dibnah] #615444
09/01/15 3:15 pm
09/01/15 3:15 pm
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kommando Offline
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This is a good resource, scroll to the bottom

http://www.sat.dundee.ac.uk/psc/spanner_jaw.html

Diff mm mm inch Spanner
0.11 11.11 0.438 7/16 AF 1/4 UNF
0.19 11.30 0.445 3/16 W; 1/4 BSF
0.70 12.00 0.472 12mm

Re: T100 cylinder base nuts, 17/32" across flats? [Re: Dibnah] #615468
09/01/15 5:31 pm
09/01/15 5:31 pm
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Posts: 10,186
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Stuart Offline
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Stuart  Offline
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Hi,

Originally Posted By Dibnah
Engine oil leaking out of the base of the barrel on my T100-engined scrambler, having problems finding the right ring spanner (wrench!), 1/2" AF is too small, 9/16" AF is too big. 14mm is slightly too big, are these nuts 17/32" across flats?
17/32" across flats must be close to 1/4" Whitworth and 5/16" BSF

As it's a '60 'C'-range Triumph, the nuts must be (British Standard) Cycle thread, all British Standard threads use the same spanner hexs. so it's the same as BSF - 0.52"AF in this case. Then, although the studs are 3/8"-dia., the nuts are small-hex, hence the 5/16" rather than the 3/8" spanner.

Originally Posted By Dibnah
There are double ring spanners available in 1/2" and 7/16" AF specifically for the cylinder base nuts on Triumph twin, assume these must be later than 1960?

When BSA, including Triumph, went to Unified threads in the late 1960's, and barrel base studs became UNC/UNF, the 6-sided small-hex. nuts available off-the-shelf in Imperial threads weren't available in Unified, there wasn't enough barrel wall thickness to the liner or bore to machine away clearance for a standard 9/16"AF 6-sided nut and spanner so, certainly in the case of the 3/8"-dia. studs, the 1/2"AF (3/8"UNF) 12-point nut was used.

Hth.

Regards,

Re: T100 cylinder base nuts, 17/32" across flats? [Re: kommando] #618281
09/20/15 11:02 am
09/20/15 11:02 am
Joined: Apr 2015
Posts: 514
UK
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Dibnah Offline OP
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Dibnah  Offline OP
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Joined: Apr 2015
Posts: 514
UK
Originally Posted By kommando
This is a good resource, scroll to the bottom

http://www.sat.dundee.ac.uk/psc/spanner_jaw.html

Diff mm mm inch Spanner
0.11 11.11 0.438 7/16 AF 1/4 UNF
0.19 11.30 0.445 3/16 W; 1/4 BSF
0.70 12.00 0.472 12mm



Thanks Kommando, a very useful link. I found reference to 17/32 across flats here http://wiki.diyfaq.org.uk/index.php?title=Size_conversion

Re: T100 cylinder base nuts, 17/32" across flats? [Re: Stuart] #618282
09/20/15 11:05 am
09/20/15 11:05 am
Joined: Apr 2015
Posts: 514
UK
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Dibnah Offline OP
BritBike Forum member
Dibnah  Offline OP
BritBike Forum member
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Joined: Apr 2015
Posts: 514
UK
Originally Posted By Stuart
Hi,

Originally Posted By Dibnah
Engine oil leaking out of the base of the barrel on my T100-engined scrambler, having problems finding the right ring spanner (wrench!), 1/2" AF is too small, 9/16" AF is too big. 14mm is slightly too big, are these nuts 17/32" across flats?
17/32" across flats must be close to 1/4" Whitworth and 5/16" BSF

As it's a '60 'C'-range Triumph, the nuts must be (British Standard) Cycle thread, all British Standard threads use the same spanner hexs. so it's the same as BSF - 0.52"AF in this case. Then, although the studs are 3/8"-dia., the nuts are small-hex, hence the 5/16" rather than the 3/8" spanner.

Originally Posted By Dibnah
There are double ring spanners available in 1/2" and 7/16" AF specifically for the cylinder base nuts on Triumph twin, assume these must be later than 1960?

When BSA, including Triumph, went to Unified threads in the late 1960's, and barrel base studs became UNC/UNF, the 6-sided small-hex. nuts available off-the-shelf in Imperial threads weren't available in Unified, there wasn't enough barrel wall thickness to the liner or bore to machine away clearance for a standard 9/16"AF 6-sided nut and spanner so, certainly in the case of the 3/8"-dia. studs, the 1/2"AF (3/8"UNF) 12-point nut was used.

Hth.

Regards,


Thanks Stuart, a 1/4" whitworth ring spanner/wrench is a good fit. I had a couple of spanners with deep offsets, couldn't get them in. Have spent some mmmmoney on a couple of flat 1/4" whit spanners found on eBay. Torqued up by feel and the leakage has stopped. Several nuts were only just more than finger tight.


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