I've been cleaning a set of old TB's and decided to remove the butterfly's... bad move - each of the little grub screws that attach the butterfly to the spindle sheared!

So going to be drilling them out - only thing is... doesn't leave much 'meat' on the spindle to tap a new thread!

So was thinking of other ways to secure them... a rivet is the obvious answer, but the reverse side of a rivet insert is never neat (in my experience) and would not be ideal for a TB set-up!

Can anyone recommend any other techniques, fasteners or fancy rivets that are flush at both end?

Ta!

Helicoil?

helicoil gos down to m2 maybe

ETA to slow

[Edited on 8/4/10 by afj]

I think you're thinking of blind rivets, inserted with a rivet gun, but originally rivets were solid, pushed through from one side and (for flush rivets) hammered down on the otherside (against a hard surface such as an anvil). The hammered side could then be fettled with a file for a smooth flush finish. For raised rivets you would need a punch with a convex end. You could (and still can I think) get them in brass and ally both of which would be an ideal solution for your need.

if you are able to drill accurately down the centre of the screw with a drill the same diameter as the core screw diameter (not sure if that is right term but the overall diameter less thread), you may be able to dig out the remainder of the thread or run a smaller size tap that will pull out the remaing screw thread.

helicoil will need a larger diameter hole and I doubt you have enough metal in the spindle for that.

you may be able to fill the hole using plumbers or some other hard solder - even lumiweld - as the spindle is likely to be brass and it is not like you are aplying 70 lbft torque to the screw


I wouldn't use rivets - they need to be solid so as not to cause an air leak.

(I am referring ofcourse to pop rivers, as opposed to the old type solid ones that you swage one end over with a hammer)

[Edited on 8/4/10 by 02GF74]

Cheers guys... and yes, it is a brass type material for both spindle and butterfly.

Hi

You need countersunk solid rivets or need to countersink the tails of mush head rivets - suggest you seek out someone in the aviation industry in your area.

Regards Mick

I wouldnt use rivets as the pressure may split the remaining "Meat" on the spindle.

I think i would either get a piece of brass rod the same size as the drilled out screw, and to exactly the right length. Once its in, you can use a centre punch (a small one) on the centre of the rod to expand it a little. Ince youve got it secure, you could then silver solder it jsut to be sure it wont come out.

They sheered off because they are peened over once screwed in to prevent them vibrating out in use.

If you are careful with a smaller drill, drill from the head side, and if your lucky the drill will grip, break the head off the screw, and screw it out the wrong way, leaving the thread intact.

Had exactly the same problem on a set of delorto carbs.

Thanks folks!