Lotus Elan and Lotus Elan Plus 2 Forums

Hi

I need to fix my bonnet bobbins, plus one headlight bobbin on my Plus 2. Thought I'd stick Helicoils in there, but what size do I need? I measure the bolt head as 7/16", 20 threads / inch, diameter .243"

Does this one look right? Hard to tell from the picture but it looks a bit big?

https://www.amazon.co.uk/V-Coil-16-inch ... B00EO4NYUQ

mbell said 1/4 20 coils: viewtopic.php?t=46122&f=51&start=0#p330463

Presume that's 1/4" 20 threads per inch?

JonB wrote:mbell said 1/4 20 coils: viewtopic.php?t=46122&f=51&start=0#p330463

Presume that's 1/4" 20 threads per inch?

Yes, that is just from memory, maybe it is 7/16"...

Maybe check the parts diagram to confirm the bolt size. The thread insert should match the bolt. So if it is 7/16"-20 that the insert size you should buy.

According to RDent's part diagrams the Bobbin bolts are XUCS0420, which translates to 1/4 UNC (20 tpi) x 1.25" long.

I tried helicoils for the bonnet but they were too short, make sure you get them to the full depth of the thread in the bobbin. I ended up replacing the bobbins, a time consuming job.

You can get Helicoils different lengths.
If the hole in the damaged Bobbin has worn ovale then you might need to use a Keyed Insert which are a larger outside dia. You may need to make a drilling plate to keep the tapping size Twist Drill central also.
Think twice and drill once
Sounds like you need a "Zeus Book" + Screw Pitch Gauge + Vernier Caliper
Good luck
Alan

7/16" is the bolt head across flats.
The thread size is 1/4" diameter x 20 tpi, which is 1/4" UNC not UNF.

I'm not sure how well helicoils would last in the alloy the pods bobbins are made of if original (they are often replaced by steel equivalent on repro body parts) : I would use complete thread inserts like Timesert or similar, and glue them in place.

For sure the keyed insert will be more durable as they will be hinge pivots. Plus the outside thread on keyed insert need only a standard Tap.
Alan

Interestingly, 1/4-20 is also the standard thread for lampshade finials. Did someone at Lotus have a bit of a sense of humour?

Just a longer term suggestion about determining thread sizes: next time you’re at the hardware store pick up a 1” long screw and nut in each thread size below, say 1/2”, fine and coarse, tag each, and keep in a bag in your shop. From then on you can immediately determine any thread’s size.

If you buy a Unified Tap and Die set it comes with a Screw Pitch Gauge. Not expensive.
Alan

Have a look at Rivnut's Jon , they are available in 1/4" 20 tpi , you will need to drill a 3/8" hole and you will have to buy the tool or borrow one, it's a great bit of kit to have anyway.

one quick word of caution : some jig (or possibly the pod itself) should be used to ensure the 2 threaded hinges are reasonably aligned for final installation in case some play has to be taken up, or there is a risk of high friction or binding in operation.

Rivnuts not a bad idea i like it but i still prefer stainless steel keyed inserts
Alan