One of the head bolts in my fp40 is stripped. I want to ask before I assume the right thing to do. I'm thinking either bore and tap it for a 3.5mm bolt, or install a helicoil for the original 3mm bolt. The latter would be my preference. I don't know anything about thread pitch so I want to make sure I can get a bolt back in after fixing the hole. Any suggestions would be appreciated. Thanks.
Rusty

 i assume u mean the case is stripped ,i would tap it out to the next bigger size bolt. not a fan of helicoils

I'm going to tap it for a 4-40 since I don't have a metric tap.

Ewwww.

I'm not sure that there will be enough meat in the hole for a 4-40 tap to do much good -- you may just end up ruining the case completely.

'course, they're still available on eBay for not too much, so it may not be that bad of a deal.

You will need  tap for a 5-40 or a 3.5mm  a 4-40  will not work

Randy

Rusty, pm me your address

Rusty - I'm pretty sure I have a 5-40 tap if you need one.

For what it's worth, I have done quite a few heads with 4-40 helicoils and never had a problem.

  Bob Z.

Okay, thanks Bob. If you'll bring it next time we fly, I'll put this plane aside and finish the job at the field. What do I need for a drill bit, 3/32, 7/64, in that neighborhood?
Rusty

My helicoil chart shows a #31 or a 3mm drill bit for the hole size.