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Frame thread sizes

Happy New Year!
Here's hoping your New Year's day has been more productive than mine. You'd think I'd know better about boozing into the small hours...

I've had a look at the technical section in the hope of finding the thread types/sizes for the frame reasembly as I'm no expert on imperial sizes. I need to heli-coil the front tank mounts and tidy various bits & pieces and a selection of the more popular taps & dies would prove useful as well as knowing what heli-coils to buy - does anyone have a list, no matter how small?

email (option): lee@twowheelstested.co.uk

Re: Frame thread sizes

Hi Lee,

All the frame bosses are 5/16 BSCY. This is a fine thread (60 degree included angle)that is supposed to resist vibration. Most of the mudguard fasteners are 1/4-26 BSCY. The only exception is the rear chain adjuster which is 1/4-20 BSW (British Standard Whitworth, 55 degree included angle).

You will need the following taps and dies to work on your bike: 1/4, 5/16, 3/8 inch BSCY (26 TPI), 7/16-20 and 1/2-20 BSCY. 5/16 BSCY is the most common.

All the engine and gearbox studs are 3/8 inch BSCY, save the lowest one on the front down tube. That one is 7/16-20. The footpegs are 1/2-20 tpi and one other through stud just beneath that is 1/2-20.

Both 7/16-20 and 1/2-20 BSCY are the same as UNF (USA-Unified National Fine. Buy these as they are not "specials" to get more money out of you.

David over at Uni-Thread is a great resource for thread repair kits. Tell him I send you OK?

MAP technical Publications has an excellent book out called "Screw Threads and Twist Drills" ISBN # 0 85242 357 8. It's prolly out of print now.

Cheers

email (option): britool51@hotmail.com

Re: Frame thread sizes

Many thanks Rob, that's really helpful.
As the tools in my garage have been metric-only until now, just one missing tool can put me back a week while I try to find it.

email (option): lee@twowheelstested.co.uk

Re: Frame thread sizes

Hi Robb.. I agree you can substitute 7/16" and 1/2" UNF for the Cycle threads you detailed. However, it should be noted any UNF nuts purchased will have a different size across the flats as Cycle Thread conforms to Whitworth dimensions in this regard.(and two of the three studs have shouldered nuts if an early pattern sumpguard is fitted)
The rear wheel/chain adjustment bolt (66-4603) is also cycle thread...perhaps the frame you looked at has been altered?...The other small thing that springs to mind is the grease nipples..they have a 1/4" BSCY/BSF thread, and the rear brake spindle boss thread..not sure from memory but is it 9/16"- 20?...Ian

email (option): ian@wright52.plus.com

Re: Frame thread sizes

Hi Ian,

Good point about the across flats dimensions of the 7/16 and 1/2 inch nuts. The US sizes work, and get me down the road until proper replacements come in from Russells.

Part number 66-6104 is 3/4-20 tpi, 60 degree included angle.

Not sure what you mean by the rear brake spindle boss though.

email (option): britool51@hotmail.com

Re: Frame thread sizes

Hi Robb..Where the rear brake lever (footbrake) spindle screws into the frame, with a locknut on the back...Ian

email (option): ian@wright52.plus.com

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