Seat belt bolts.

[Classic Chim]

Can anyone confirm the size and thread used on seat belt anchor bolts ( into Chassis bottom rails ) so inner spar.
I’ve successfully drilled out my front chassis bolt leaving a perfect thread,
I’ve done the same with spar bolt but it’s still got metal in there.
Is this larger than chassis bolts 7/16 UNF ?

[Dougal9887]

Same thread, 7/16" UNF.
Dougal.

[Classic Chim]

Dougal9887 said:

Same thread, 7/16" UNF.
Dougal.

That’s what I thought!
I need better glasses as I’ve obviously still a drill size to go up.
Front chassis bolt drilled out a treat with the correct sized unf bits. I even bought a new punch
I’m pretty useless with English sizes and just got the techi at my metal shop to give me the correct final bit size to drill it out without hitting thread, I’ll come back with the sizes as it’s useful for someone later. I’ll run a tap through them but the front bolt ran in fine.
Thanks.

[Dougal9887]

The correct tapping drill for 7/16" is 9.9mm.
Dougal.

Edited by Dougal9887 on Tuesday 21st January 22:12

[Steve_D]

Classic Chim said:

Can anyone confirm the size and thread used on seat belt anchor bolts ( into Chassis bottom rails ) so inner spar.
I’ve successfully drilled out my front chassis bolt leaving a perfect thread,
I’ve done the same with spar bolt but it’s still got metal in there.
Is this larger than chassis bolts 7/16 UNF ?

Bit confused by this.
When you say 'front chassis bolt leaving a perfect thread' are you referring to a seatbelt bolts or the body bolts into the front of the chassis rails?

Reason I ask is that the seatbelt bolts are tapped 7/16 UNF (4 holes) all other tapped holes are metric.

Steve

[Badgerchim]

The reference section of this excellent and hugely informative write up lists the various seat belt bolts in detail

https://chimrebuild.wordpress.com/

[Dougal9887]

Tapping drill for the remainder, metric 10mm, is 8.5mm.
Dougal

[sjwb]

Erm, tapping for a 7/16” UNF is .3898” or if you must, 9.90mm.

[Classic Chim]

Steve_D said:

Bit confused by this.
When you say 'front chassis bolt leaving a perfect thread' are you referring to a seatbelt bolts or the body bolts into the front of the chassis rails?

Reason I ask is that the seatbelt bolts are tapped 7/16 UNF (4 holes) all other tapped holes are metric.

Steve

I can see what I’ve done here now.
Chassis bolts at the front are metric and smaller, I’ve used drill bits for seat anchors which are UNF and drilled out the metric bolt, this seems to have been a perfect fit as the last drill literally turned the final bits of steel out so not effecting thread at all, I will take a pic when I can.
I’ve then used these bits to drill out the seat belt anchor bolt which is 7/16 this has left enough of the bolt to tap it out so the drill bit seller assumed I’d want to tap the last bit out which is the correct way to do it and the way I will do it.
I think the fact I’ve drilled a lot of bolts out over the years and I know how to keep my drill central to the hole has saved me from knackering the metric thread. Pillock for not realising chassis bolts are metric.

Edited by Classic Chim on Tuesday 21st January 15:33

[Classic Chim]

Badgerchim said:

The reference section of this excellent and hugely informative write up lists the various seat belt bolts in detail

https://chimrebuild.wordpress.com/

I used this very write up to take the car apart, that and people’s advice. I’d sort of read it then go do each task. This excellent information is indeed easy to follow, pity I hadn’t looked at the specification sheet. I’d recommend this write up as a good way to be working methodically.
Some things I’ve done slightly different but basically followed this guide. Worked a treat.

[Dougal9887]

sjwb said:

Erm, tapping for a 7/16” UNF is .3898” or if you must, 9.90mm.

Oops, not sure where that rubbish came from!

You are of course quite correct. I'll amend my post to avoid confusion!
Dougal.