Bonnet bobbin threads

[Nic]

Hi, can anyone confirm what the thread is in the bonnet bobbins (bonnet bolt). I need to get a helicoil repair kit as there is just an oversized hole in the body bobbin.
Nic

[Bud English]

Nik- They are 1/4-20 threads.

Try to get a long helicoil with as much thread area as possible. The bobbins in the body, the bobbins in the bonnet, and the bolts are the "hinge" and work every time the bonnet is opened. The bolt should be fully threaded and long enough to go into the body bobbin at least 1/2 to 5/8. That bolt isn't called out specifically in the parts manual but it should be. Too short a bolt and you end up with what you have.

[Nic]

Many thanks Bud

[mbell]

I think I fitted 2" bolts. I found both the bobbins on my car were not threaded so went for a none fully threaded bolt and nut on the engine bay side.

Not sure if the bobbins were original thread and modified by a PO or not but I'd check yours first.

[Nic]

The holes on my body bobbins are excessively large, perhaps they had an insert that fell out at some time in the past? I was planning on sleeving these with alumininium dowels ( which I will helicoil) and will use a permanent lock-tight on the dowels

[Bud English]

All four bobbins, body and bonnet, were originally fully threaded. The alignment of the bonnet, side to side, is maintained by the bolts and the number of threads in the open area between the body and bonnet. Works the same way as the the "hinges" on the light pods. Added lightness- no hinges and no washers. Some say cheap, and some genius.

[Sea Ranch]

Yup; well put, Bud.

I would say "genius", but the bonnet is a royal pain to re-install and get centered. Made up various jigs, but it's still a royal pain.

[rgh0]

As the threads stripped out on the bonnet or wheel arch of my Plus 2 I just left them out and fitted a bolt and nut
Once you have one threaded or none threaded on each side it becomes much easier to centre the bonnet in the opening than with both the bonnet and wheel arch threads all still in place.

Having bolts turn in threaded Bobbins is also a strange practice even if it did save the weight and cost of a nut ( at the expense of tapping the bobbins). Much better to lock it in a threaded Bobbin and have it turn in a plain Bobbin.

cheers
Rohan

[Sea Ranch]

Yes; agreed, Rohan.

Interesting, though, that when both bobbins on a side are threaded, you have a built in spacing device which keeps the bonnet centered where you put it (otherwise, you'd need washers/spacers between bonnet and wing). Though even more interestingly, the bonnet actually shifts from one side to the other a little when it's raised, as the bonnet travels a quarter turn along the threads of the two mounting bolts. Same with the headlamp bowls. Crazy!

[rgh0]

I dont use spacer washers. I rely on setting up the bolts on either side so they stop the bonnet moving in tension.

cheers
Rohan

[Spyder fan]

My 1969 powerbulge +2S bonnet has 5/16 UNC bobbins in the bonnet and wings, I have an early +2 flat bonnet which is the more familiar 1/4 UNC and a modern reproduction that also came with 1/4 UNC.

I have the modern replacement fitted at the moment and agonised at what to do to fix it in place, but in the end I just used longer bolts and nuts as per Rohan's solution.

For information: The originals are far better quality than the reproduction, but the new ones do add lightness being quite flimsy.