1966 Lightning front wheel spindle clamp bolt

[DJC]

Hi - Does anyone know what the correct thread form should be for the front wheel spindle clamp bolt in the left hand fork leg please. Somebody has forced an obviously incorrect bolt into mine and I need to recaim it. I'm guessing UNF but maybe cycle ?
Thanks

[JulianS]

3/8 x 26 tpi cycle.

UNF threads not adopted by BSA until 1969.

[Nanonevol]

https://partsbooks.britishonly.com/partsbooks/20-10205C.pdf

http://www.gregmarsh.com/MC/FastenersList.aspx

[DJC]

Thanks guys. Cycle it is.
Just to add confusion to the equation though, there are definitely some UNF threads on my bike - example being the bolt that holds the swing arm spindle end plate into the frame, the new bolt supplied with the new swing arm is UNF and its a match for the thread in the frame. There are others but I cant remember which ones just now.
Now to tackle that fork leg - theres not much thread left so it might not be easy (not enough meat for a simple helicoil). Anyway, it will be done one way or the other.
Cheers all

[Mike Farmer]

 

Hi I have a similar problem where the wrong thread appears to have been either forced or tapped into the legs thus making mine a very bad fit.

I am seriously considering do a small countersink and then brazing studs in. Not the ideal solution but better I think than riding with dodgy bolts.

I once had a bike with studs instead of bolts and I'm now wondering if that was done by someone with the same problem?

Your views and other ideas very welcome.

Mike

[DAVE BRADY]

Hi Mike,

Later A65 has studs and I think B25 also. 

Dave.

[BruceB]

Mine has a nut and bolt straight through both sides, hadn't realised it was a bodge until now.

[DJC]

Hi - sorry for late response.
I tapped out what was left of the thread (cycle) and ended up with sufficient thread to take the bolt and to nip up the spindle. However, I wasnt happy that the thread would take 'proper' tightening or that if it did, how long it might last. Being safety critical, I therefore decided on a belt and braces approach. I little bit of filing of the leg behind the threaded portion produced sufficient land to fit a spring washer and nut onto a slightly longer bolt than standard, so I can now lock the bolt in position. The only other option would have been to weld and re-drill and tap a new thread.

[Bess]

Hi,
    Unfortunately spring washers do not stop fixings loosening.

https://www.boltscience.com/pages/helicalspringwashers.htm

Your best option is to fit studs, washers and locknuts.

Best wishes...

[Mike Farmer]

 

I have also considered making double size bolts/studs  something like 11/32 up into the leg with a 5/16 shank to go through the end cap then fix with a washer and nylok. That's as an alternative to brazing a stud in. The "inner" end could probably go up to 3/8 but that,s questionable.

Mike

[Bess]

Hi Mike,
             If originality is an issue worth considering a Time-sert.

Best wishes...

[Mike Farmer]

 

Its on my trike so originality does really mean much.

What is a time sert?

Mike

[Bess]

Hi Mike,
            Similar to a helicoil, its of solid thin wall construction with a small flange. Its preferred over helicoils where the hole isn't blind and a carries a larger load.

https://www.wurth.ie/media/downloads/pdf/short_form_catalogues/Timesert.pdf

Like you I am not bothered with originality. Personally I would helicoil the leg and fit a high tensile stud, safer and long lasting.

Bet wishes...

[Nanonevol]

Its on my trike so originality does really mean much.

What is a time sert?

Mike

A 1966 Lightning Trike? 
Oh we need a photo of that?

[Mike Farmer]

 

No its a 1963 A50 Trike.