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I need to know the thread size for the GB index plunger housing. A helicoil is necessary.
GB index plunger
- Thread starter seattle##gs
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Go to
armed with part number.
If its not listed then get out the digital caliper to measure the diameter, TPI gauge to get the thread TPI and then Google.
For someone who works on loads of bikes, just seen for the first time, you should be doing this anyway, in case some DPO has fitted a rogue fitting and the thread is non-standard.
Fastener Database
Greg Marsh Enterprises Vintage British Motorcycle Parts and Service
www.gregmarsh.com
armed with part number.
If its not listed then get out the digital caliper to measure the diameter, TPI gauge to get the thread TPI and then Google.
For someone who works on loads of bikes, just seen for the first time, you should be doing this anyway, in case some DPO has fitted a rogue fitting and the thread is non-standard.
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The same 040036 plunger housing part number is listed for AMC and Commando so it is probably either 55° special Whitworth or
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The 20 TPI thread form from a (3/8) cylinder head stud fit the plunger thread close to perfect. ?
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The difficulty is probably finding a 5/8"- 20 Helicoil of any description.
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Walridge Motors lists helicoil kits for old bike threads - not sure they have one in that size - may be worth calling them. Their catalog only goes up to 1/2" CEI (BSC).
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An option would be to helicoil it to 5/8"-18 (standard UNF thread), and then have a custom plunger housing machined - it is not a complex part.
FWIW
FWIW
marshg246
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British Fasteners: https://britishfasteners.com/ probably has them but you need to call with the actual bolt diameter and TPI and get them to translate to the British size - I'm guessing 5/8-20 BSF but that's the wrench size, not the diameter of the bolt (I'm NOT as British thread expert!!!). Remember that British sizes are not measured the same as UNC/UNF. You can be sure that is not UNF or UNC.
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marshg246
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Ya, tried hard but still got it balled up. Just measured the hole in a gearbox case - basically 9/16". What is the "size" of that?
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It's 5/8" according to Time Warp.
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At 20 TPI its likely to be cycle thread, cycle has the option for 20 TPI on large diameters instead of the usual 26 TPI.
A helicoil kit will likely be impossible to find, so get the hole welded up after making a template for the hole centre position, drill for a 5/8 20 TPI tap which is available in cycle thread.
A helicoil kit will likely be impossible to find, so get the hole welded up after making a template for the hole centre position, drill for a 5/8 20 TPI tap which is available in cycle thread.
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Correction.
Previously, I said:
However:
According to the BS811:1950 specifications for British Standard Cycle thread, the 20 TPI series were (BS84) "British Standard Whitworth form", therefore, also 55°, not 60°.
Previously, I said:
However:
According to the BS811:1950 specifications for British Standard Cycle thread, the 20 TPI series were (BS84) "British Standard Whitworth form", therefore, also 55°, not 60°.
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Walridge says they MIGHT be able to get one, approx $150 and who knows how long to get it. Another possibility is to make one with american thread and helicoil the case to suit. There isn't a lot of material in the boss to work with. The part would be easy to make in a lathe.
marshg246
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Is the gearbox case a numbers match with the engine? If not, or you don't care, a used case might cost less.
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Your gearbox acronym “GB” threw me. I’m working on a ‘56 AJS with a Burman GB gearbox as opposed to CP gearbox. Couldn’t understand why you would have a Burman in a Commando….finally got it.
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This is for a friend who stripped out the hole in a spare box so not a big priority. He just wanted to repair it with a helicoil and be done.
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